NETMOD L. Lhotka, Ed.
Internet-Draft CESNET
Intended status: Standards Track September 28, 2010
Expires: April 1, 2011
Mapping YANG to Document Schema Definition Languages and Validating
NETCONF Content
draft-ietf-netmod-dsdl-map-08
Abstract
This document specifies the mapping rules for translating YANG data
models into Document Schema Definition Languages (DSDL), a
coordinated set of XML schema languages standardized as ISO/IEC
19757. The following DSDL schema languages are addressed by the
mapping: RELAX NG, Schematron and DSRL. The mapping takes one or
more YANG modules and produces a set of DSDL schemas for a selected
target document type - datastore content, NETCONF message etc.
Procedures for schema-based validation of such documents are also
discussed.
Status of this Memo
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This Internet-Draft will expire on April 1, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 8
2.1. Glossary of New Terms . . . . . . . . . . . . . . . . . 11
3. Objectives and Motivation . . . . . . . . . . . . . . . . . . 12
4. DSDL Schema Languages . . . . . . . . . . . . . . . . . . . . 14
4.1. RELAX NG . . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. Schematron . . . . . . . . . . . . . . . . . . . . . . . 15
4.3. Document Semantics Renaming Language (DSRL) . . . . . . 16
5. Additional Annotations . . . . . . . . . . . . . . . . . . . 17
5.1. Dublin Core Metadata Elements . . . . . . . . . . . . . 17
5.2. RELAX NG DTD Compatibility Annotations . . . . . . . . . 17
5.3. NETMOD-Specific Annotations . . . . . . . . . . . . . . 18
6. Overview of the Mapping . . . . . . . . . . . . . . . . . . . 20
7. NETCONF Content Validation . . . . . . . . . . . . . . . . . 22
8. Design Considerations . . . . . . . . . . . . . . . . . . . . 23
8.1. Hybrid Schema . . . . . . . . . . . . . . . . . . . . . 23
8.2. Modularity . . . . . . . . . . . . . . . . . . . . . . . 25
8.3. Granularity . . . . . . . . . . . . . . . . . . . . . . 27
8.4. Handling of XML Namespaces . . . . . . . . . . . . . . . 27
9. Mapping YANG Data Models to the Hybrid Schema . . . . . . . . 29
9.1. Occurrence Rules for Data Nodes . . . . . . . . . . . . 29
9.1.1. Optional and Mandatory Nodes . . . . . . . . . . . 30
9.1.2. Implicit Nodes . . . . . . . . . . . . . . . . . . 31
9.2. Mapping YANG Groupings and Typedefs . . . . . . . . . . 32
9.2.1. YANG Refinements and Augments . . . . . . . . . . . 33
9.2.2. Type Derivation Chains . . . . . . . . . . . . . . 36
9.3. Translation of XPath Expressions . . . . . . . . . . . . 38
9.4. YANG Language Extensions . . . . . . . . . . . . . . . . 39
10. Mapping YANG Statements to the Hybrid Schema . . . . . . . . 41
10.1. The 'anyxml' Statement . . . . . . . . . . . . . . . . . 41
10.2. The 'argument' Statement . . . . . . . . . . . . . . . . 42
10.3. The 'augment' Statement . . . . . . . . . . . . . . . . 43
10.4. The 'base' Statement . . . . . . . . . . . . . . . . . . 43
10.5. The 'belongs-to' Statement . . . . . . . . . . . . . . . 43
10.6. The 'bit' Statement . . . . . . . . . . . . . . . . . . 43
10.7. The 'case' Statement . . . . . . . . . . . . . . . . . . 43
10.8. The 'choice' Statement . . . . . . . . . . . . . . . . . 43
10.9. The 'config' Statement . . . . . . . . . . . . . . . . . 44
10.10. The 'contact' Statement . . . . . . . . . . . . . . . . 44
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10.11. The 'container' Statement . . . . . . . . . . . . . . . 44
10.12. The 'default' Statement . . . . . . . . . . . . . . . . 44
10.13. The 'description' Statement . . . . . . . . . . . . . . 46
10.14. The 'deviation' Statement . . . . . . . . . . . . . . . 46
10.15. The 'enum' Statement . . . . . . . . . . . . . . . . . . 46
10.16. The 'error-app-tag' Statement . . . . . . . . . . . . . 46
10.17. The 'error-message' Statement . . . . . . . . . . . . . 46
10.18. The 'extension' Statement . . . . . . . . . . . . . . . 46
10.19. The 'feature' Statement . . . . . . . . . . . . . . . . 46
10.20. The 'grouping' Statement . . . . . . . . . . . . . . . . 46
10.21. The 'identity' Statement . . . . . . . . . . . . . . . . 47
10.22. The 'if-feature' Statement . . . . . . . . . . . . . . . 48
10.23. The 'import' Statement . . . . . . . . . . . . . . . . . 49
10.24. The 'include' Statement . . . . . . . . . . . . . . . . 49
10.25. The 'input' Statement . . . . . . . . . . . . . . . . . 49
10.26. The 'key' Statement . . . . . . . . . . . . . . . . . . 49
10.27. The 'leaf' Statement . . . . . . . . . . . . . . . . . . 49
10.28. The 'leaf-list' Statement . . . . . . . . . . . . . . . 50
10.29. The 'length' Statement . . . . . . . . . . . . . . . . . 50
10.30. The 'list' Statement . . . . . . . . . . . . . . . . . . 51
10.31. The 'mandatory' Statement . . . . . . . . . . . . . . . 52
10.32. The 'max-elements' Statement . . . . . . . . . . . . . . 52
10.33. The 'min-elements' Statement . . . . . . . . . . . . . . 52
10.34. The 'module' Statement . . . . . . . . . . . . . . . . . 52
10.35. The 'must' Statement . . . . . . . . . . . . . . . . . . 53
10.36. The 'namespace' Statement . . . . . . . . . . . . . . . 53
10.37. The 'notification' Statement . . . . . . . . . . . . . . 54
10.38. The 'ordered-by' Statement . . . . . . . . . . . . . . . 54
10.39. The 'organization' Statement . . . . . . . . . . . . . . 54
10.40. The 'output' Statement . . . . . . . . . . . . . . . . . 54
10.41. The 'path' Statement . . . . . . . . . . . . . . . . . . 54
10.42. The 'pattern' Statement . . . . . . . . . . . . . . . . 54
10.43. The 'position' Statement . . . . . . . . . . . . . . . . 55
10.44. The 'prefix' Statement . . . . . . . . . . . . . . . . . 55
10.45. The 'presence' Statement . . . . . . . . . . . . . . . . 55
10.46. The 'range' Statement . . . . . . . . . . . . . . . . . 55
10.47. The 'reference' Statement . . . . . . . . . . . . . . . 55
10.48. The 'require-instance' Statement . . . . . . . . . . . . 55
10.49. The 'revision' Statement . . . . . . . . . . . . . . . . 55
10.50. The 'rpc' Statement . . . . . . . . . . . . . . . . . . 55
10.51. The 'status' Statement . . . . . . . . . . . . . . . . . 56
10.52. The 'submodule' Statement . . . . . . . . . . . . . . . 56
10.53. The 'type' Statement . . . . . . . . . . . . . . . . . . 56
10.53.1. The "empty" Type . . . . . . . . . . . . . . . . . 57
10.53.2. The "boolean" and "binary" Types . . . . . . . . . 58
10.53.3. The "bits" Type . . . . . . . . . . . . . . . . . . 58
10.53.4. The "enumeration" and "union" Types . . . . . . . . 58
10.53.5. The "identityref" Type . . . . . . . . . . . . . . 58
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10.53.6. The "instance-identifier" Type . . . . . . . . . . 59
10.53.7. The "leafref" Type . . . . . . . . . . . . . . . . 59
10.53.8. The Numeric Types . . . . . . . . . . . . . . . . . 59
10.53.9. The "string" Type . . . . . . . . . . . . . . . . . 61
10.53.10. Derived Types . . . . . . . . . . . . . . . . . . . 62
10.54. The 'typedef' Statement . . . . . . . . . . . . . . . . 63
10.55. The 'unique' Statement . . . . . . . . . . . . . . . . . 63
10.56. The 'units' Statement . . . . . . . . . . . . . . . . . 64
10.57. The 'uses' Statement . . . . . . . . . . . . . . . . . . 64
10.58. The 'value' Statement . . . . . . . . . . . . . . . . . 64
10.59. The 'when' Statement . . . . . . . . . . . . . . . . . . 64
10.60. The 'yang-version' Statement . . . . . . . . . . . . . . 64
10.61. The 'yin-element' Statement . . . . . . . . . . . . . . 64
11. Mapping the Hybrid Schema to DSDL . . . . . . . . . . . . . . 65
11.1. Generating RELAX NG Schemas for Various Document Types . 65
11.2. Mapping Semantic Constraints to Schematron . . . . . . . 66
11.2.1. Constraints on Mandatory Choice . . . . . . . . . . 69
11.3. Mapping Default Values to DSRL . . . . . . . . . . . . . 70
12. Mapping NETMOD-specific Annotations to DSDL Schema
Languages . . . . . . . . . . . . . . . . . . . . . . . . . . 76
12.1. The @nma:config Annotation . . . . . . . . . . . . . . . 76
12.2. The @nma:default Annotation . . . . . . . . . . . . . . 76
12.3. The <nma:error-app-tag> Annotation . . . . . . . . . . . 76
12.4. The <nma:error-message> Annotation . . . . . . . . . . . 76
12.5. The @if-feature Annotation . . . . . . . . . . . . . . . 76
12.6. The @nma:implicit Annotation . . . . . . . . . . . . . . 77
12.7. The <nma:instance-identifier> Annotation . . . . . . . . 77
12.8. The @nma:key Annotation . . . . . . . . . . . . . . . . 77
12.9. The @nma:leaf-list Annotation . . . . . . . . . . . . . 77
12.10. The @nma:leafref Annotation . . . . . . . . . . . . . . 78
12.11. The @nma:min-elements Annotation . . . . . . . . . . . . 78
12.12. The @nma:max-elements Annotation . . . . . . . . . . . . 78
12.13. The <nma:must> Annotation . . . . . . . . . . . . . . . 78
12.14. The <nma:ordered-by> Annotation . . . . . . . . . . . . 79
12.15. The <nma:status> Annotation . . . . . . . . . . . . . . 79
12.16. The @nma:unique Annotation . . . . . . . . . . . . . . . 79
12.17. The @nma:when Annotation . . . . . . . . . . . . . . . . 79
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 80
14. Security Considerations . . . . . . . . . . . . . . . . . . . 81
15. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 82
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 83
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 84
17.1. Normative References . . . . . . . . . . . . . . . . . . 84
17.2. Informative References . . . . . . . . . . . . . . . . . 85
Appendix A. RELAX NG Schema for NETMOD-Specific Annotations . . 87
Appendix B. Schema-Independent Library . . . . . . . . . . . . . 92
Appendix C. Mapping DHCP Data Model - A Complete Example . . . . 93
C.1. Input YANG Module . . . . . . . . . . . . . . . . . . . 93
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C.2. Hybrid Schema . . . . . . . . . . . . . . . . . . . . . 95
C.3. Final DSDL Schemas . . . . . . . . . . . . . . . . . . . 100
C.3.1. Main RELAX NG Schema for <nc:get> Reply . . . . . . 101
C.3.2. RELAX NG Schema - Global Named Pattern
Definitions . . . . . . . . . . . . . . . . . . . . 103
C.3.3. Schematron Schema for <nc:get> Reply . . . . . . . 105
C.3.4. DSRL Schema for <nc:get> Reply . . . . . . . . . . 107
Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 108
D.1. Changes Between Versions -07 and -08 . . . . . . . . . . 108
D.2. Changes Between Versions -06 and -07 . . . . . . . . . . 108
D.3. Changes Between Versions -05 and -06 . . . . . . . . . . 108
D.4. Changes Between Versions -04 and -05 . . . . . . . . . . 109
D.5. Changes Between Versions -03 and -04 . . . . . . . . . . 109
D.6. Changes Between Versions -02 and -03 . . . . . . . . . . 110
D.7. Changes Between Versions -01 and -02 . . . . . . . . . . 111
D.8. Changes Between Versions -00 and -01 . . . . . . . . . . 111
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 113
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1. Introduction
The NETCONF Working Group has completed a base protocol used for
configuration management [RFC4741]. This base specification defines
protocol bindings and an XML container syntax for configuration and
management operations, but does not include a data modeling language
or accompanying rules for how to model configuration and state
information carried by NETCONF. The IETF Operations Area has a long
tradition of defining data for SNMP Management Information Bases
(MIB) modules [RFC1157] using the Structure of Management Information
(SMI) language [RFC2578] to model its data. While this specific
modeling approach has a number of well-understood problems, most of
the data modeling features provided by SMI are still considered
extremely important. Simply modeling the valid syntax without the
additional semantic relationships has caused significant
interoperability problems in the past.
The NETCONF community concluded that a data modeling framework is
needed to support ongoing development of IETF and vendor-defined
management information modules. The NETMOD Working Group was
chartered to design a modeling language defining the semantics of
operational data, configuration data, event notifications and
operations, with focus on "human-friendliness", i.e., readability and
ease of use. The result is the YANG data modeling language
[RFC6020], which now serves for the normative description of NETCONF
data models.
Since NETCONF uses XML for encoding its messages, it is natural to
express the constraints on NETCONF content using standard XML schema
languages. For this purpose, the NETMOD WG selected the Document
Schema Definition Languages (DSDL) that is being standardized as ISO/
IEC 19757 [DSDL]. The DSDL framework comprises a set of XML schema
languages that address grammar rules, semantic constraints and other
data modeling aspects, but also, and more importantly, do it in a
coordinated and consistent way. While it is true that some DSDL
parts have not been standardized yet and are still work in progress,
the three parts that the YANG-to-DSDL mapping relies upon - Regular
Language for XML Next Generation (RELAX NG), Schematron and Document
Schema Renaming Language (DSRL) - already have the status of an ISO/
IEC International Standard and are supported in a number of software
tools.
This document contains a specification of a mapping that translates
YANG data models to XML schemas utilizing a subset of the DSDL schema
languages. The mapping procedure is divided into two steps: In the
first step, the structure of the data tree, signatures of remote
procedure call (RPC) operations and notifications is expressed as the
so-called "hybrid schema" - a single RELAX NG schema with annotations
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representing additional data model information (metadata,
documentation, semantic constraints, default values etc.). The
second step then generates a coordinated set of DSDL schemas that can
be used for validating specific XML documents such as client
requests, server responses or notifications, perhaps also taking into
account additional context such as active capabilities or features.
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2. Terminology and Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The following terms are defined in [RFC4741]:
o client
o datastore
o message
o operation
o server
The following terms are defined in [RFC6020]:
o augment
o base type
o built-in type
o configuration data
o container
o data model
o data node
o data tree
o derived type
o device deviation
o extension
o feature
o grouping
o instance identifier
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o leaf-list
o list
o mandatory node
o module
o RPC
o RPC operation
o schema node
o schema tree
o state data
o submodule
o top-level data node
o uses
The following terms are defined in [XML-INFOSET]:
o attribute
o document
o document element
o document type declaration (DTD)
o element
o information set
o namespace
In the text, the following typographic conventions are used:
o YANG statement keywords are delimited by single quotes.
o XML element names are delimited by "<" and ">" characters.
o Names of XML attributes are prefixed by the "@" character.
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o Other literal values are delimited by double quotes.
XML elements names are always written with explicit namespace
prefixes corresponding to the following XML vocabularies:
"a" DTD compatibility annotations [RNG-DTD];
"dc" Dublin Core metadata elements [RFC5013];
"dsrl" Document Semantics Renaming Language [DSRL];
"en" NETCONF event notifications [RFC5277];
"nc" NETCONF protocol [RFC4741];
"nma" NETMOD-specific schema annotations (see Section 5.3);
"nmf" NETMOD-specific XPath extension functions (see Section 12.7);
"rng" RELAX NG [RNG];
"sch" ISO Schematron [Schematron];
"xsd" W3C XML Schema [XSD].
The following table shows the mapping of these prefixes to namespace
URIs.
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+--------+-----------------------------------------------------+
| Prefix | Namespace URI |
+--------+-----------------------------------------------------+
| a | http://relaxng.org/ns/compatibility/annotations/1.0 |
| | |
| dc | http://purl.org/dc/terms |
| | |
| dsrl | http://purl.oclc.org/dsdl/dsrl |
| | |
| en | urn:ietf:params:xml:ns:netconf:notification:1.0 |
| | |
| nc | urn:ietf:params:xml:ns:netconf:base:1.0 |
| | |
| nma | urn:ietf:params:xml:ns:netmod:dsdl-annotations:1 |
| | |
| nmf | urn:ietf:params:xml:ns:netmod:xpath-extensions:1 |
| | |
| rng | http://relaxng.org/ns/structure/1.0 |
| | |
| sch | http://purl.oclc.org/dsdl/schematron |
| | |
| xsd | http://www.w3.org/2001/XMLSchema |
+--------+-----------------------------------------------------+
Table 1: Used namespace prefixes and corresponding URIs
2.1. Glossary of New Terms
o ancestor datatype: Any datatype a given datatype is (transitively)
derived from.
o ancestor built-in datatype: The built-in datatype that is at the
start of the type derivation chain for a given datatype.
o hybrid schema: A RELAX NG schema with annotations, which embodies
the same information as the source YANG module(s). See
Section 8.1 for details.
o implicit node: A data node that, if it is not instantiated in a
data tree, may be added to the information set of that data tree
(configuration, RPC input or output, notification) without
changing the semantics of the data tree.
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3. Objectives and Motivation
The main objective of this work is to complement YANG as a data
modeling language with validation capabilities of DSDL schema
languages, namely RELAX NG, Schematron and DSRL. This document
describes the correspondence between grammatical, semantic and data
type constraints expressed in YANG and equivalent DSDL patterns and
rules. The ultimate goal is to be able to capture all substantial
information contained in YANG modules and express it in DSDL schemas.
While the mapping from YANG to DSDL described in this document may in
principle be invertible, the inverse mapping from DSDL to YANG is
beyond the scope of this document.
XML-based information models and XML-encoded data appear in several
different forms in various phases of YANG data modeling and NETCONF
workflow - configuration datastore contents, RPC requests and
replies, and notifications. Moreover, RPC operations are
characterized by an inherent diversity resulting from selective
availability of capabilities and features. YANG modules can also
define new RPC operations. The mapping should be able to accommodate
this variability and generate schemas that are specifically tailored
to a particular situation and thus considerably more effective for
validation than generic all-encompassing schemas.
In order to cope with this variability, we assume that the DSDL
schemas will be generated on demand for a particular purpose from the
available collection of YANG modules and their lifetime will be
relatively short. In other words, we don't envision that any
collection of DSDL schemas will be created and maintained over an
extended period of time in parallel to YANG modules.
The generated schemas are primarily intended as input to existing XML
schema validators and other off-the-shelf tools. However, the
schemas may also be perused by developers and users as a formal
representation of constraints on a particular XML-encoded data
object. Consequently, our secondary goal is to keep the schemas as
readable as possible. To this end, the complexity of the mapping is
distributed into two steps:
1. The first step maps one or more YANG modules to the so-called
hybrid schema, which is a single RELAX NG schema that describes
grammatical constraints for the main data tree as well as for RPC
operations and notifications. Semantic constraints and other
information appearing in the input YANG modules is recorded in
the hybrid schema in the form of foreign namespace annotations.
The output of the first step can thus be considered a virtually
complete equivalent of the input YANG modules.
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2. In the second step, the hybrid schema from step 1 is transformed
further to a coordinated set of fully conformant DSDL schemas
containing constraints for a particular data object and a
specific situation. The DSDL schemas are intended mainly for
machine validation using off-the-shelf tools.
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4. DSDL Schema Languages
Document Schema Definition Languages (DSDL) is a framework of schema
languages that is being developed as the International Standard ISO/
IEC 19757 [DSDL]. Unlike other approaches to XML document
validation, most notably W3C XML Schema Definition (XSD) [XSD], the
DSDL framework adheres to the principle of "small languages": Each of
the DSDL constituents is a stand-alone schema language with a
relatively narrow purpose and focus. Together, these schema
languages may be used in a coordinated way to accomplish various
validation tasks.
The mapping described in this document uses three of the DSDL schema
languages, namely RELAX NG [RNG], Schematron [Schematron] and DSRL
[DSRL].
4.1. RELAX NG
RELAX NG (pronounced "relaxing") is an XML schema language for
grammar-based validation and Part 2 of the ISO/IEC DSDL family of
standards [RNG]. Like the W3C XML Schema language [XSD], it is able
to describe constraints on the structure and contents of XML
documents. However, unlike the DTD [XML] and XSD schema languages,
RELAX NG intentionally avoids any infoset augmentation such as
defining default values. In the DSDL architecture, the particular
task of defining and applying default values is delegated to another
schema language, DSRL (see Section 4.3).
As its base datatype library, RELAX NG uses the W3C XML Schema
Datatype Library [XSD-D], but unlike XSD, other datatype libraries
may be used along with it or even replace it if necessary.
RELAX NG is very liberal in accepting annotations from other
namespaces. With a few exceptions, such annotations may be placed
anywhere in the schema and need no encapsulating elements such as
<xsd:annotation> in XSD.
RELAX NG schemas can be represented in two equivalent syntaxes: XML
and compact. The compact syntax is described in Annex C of the RELAX
NG specification [RNG-CS], which was added to the standard in 2006
(Amendment 1). Automatic bidirectional conversions between the two
syntaxes can be accomplished using several tools, for example Trang
[Trang].
For its terseness and readability, the compact syntax is often the
preferred form for publishing RELAX NG schemas whereas validators and
other software tools usually work with the XML syntax. However, the
compact syntax has two drawbacks:
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o External annotations make the compact syntax schema considerably
less readable. While in the XML syntax the annotating elements
and attributes are represented in a simple and uniform way (XML
elements and attributes from foreign namespaces), the compact
syntax uses as many as four different syntactic constructs:
documentation, grammar, initial and following annotations.
Therefore, the impact of annotations on readability is often much
stronger for the compact syntax than it is for the XML syntax.
o In a computer program, it is more difficult to generate the
compact syntax than the XML syntax. While a number of software
libraries exist that make it easy to create an XML tree in the
memory and then serialize it, no such aid is available for the
compact syntax.
For these reasons, the mapping specification in this document uses
exclusively the XML syntax. Where appropriate, though, the schemas
resulting from the translation MAY be presented in the equivalent
compact syntax.
RELAX NG elements are qualified with the namespace URI
"http://relaxng.org/ns/structure/1.0". The namespace of the W3C
Schema Datatype Library is
"http://www.w3.org/2001/XMLSchema-datatypes".
4.2. Schematron
Schematron is Part 3 of DSDL that reached the status of a full ISO/
IEC standard in 2006 [Schematron]. In contrast to the traditional
schema languages such as DTD, XSD or RELAX NG, which are based on the
concept of a formal grammar, Schematron utilizes a rule-based
approach. Its rules may specify arbitrary conditions involving data
from different parts of an XML document. Each rule consists of three
essential components:
o context - an XPath expression that defines the set of locations
where the rule is to be applied;
o assert or report condition - another XPath expression that is
evaluated relative to the location matched by the context
expression;
o human-readable message that is displayed when the assert condition
is false or report condition is true.
The difference between the assert and report condition is that the
former is positive in that it states a condition that a valid
document has to satisfy, whereas the latter specifies an error
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condition.
Schematron draws most of its expressive power from XPath [XPath] and
Extensible Stylesheet Language Transformations (XSLT) [XSLT]. ISO
Schematron allows for dynamic query language binding so that the
following XML query languages can be used: STX, XSLT 1.0, XSLT 1.1,
EXSLT, XSLT 2.0, XPath 1.0, XPath 2.0 and XQuery 1.0 (this list may
be extended in the future).
Human-readable error messages are another feature that sets
Schematron apart from other common schema languages. The messages
may even contain XPath expressions that are evaluated in the actual
context and thus refer to information items in the XML document being
validated.
Another feature of Schematron that is used by the mapping are
abstract patterns. These work essentially as macros and may also
contain parameters which are supplied when the abstract pattern is
used.
Schematron elements are qualified with namespace URI
"http://purl.oclc.org/dsdl/schematron".
4.3. Document Semantics Renaming Language (DSRL)
DSRL (pronounced "disrule") is Part 8 of DSDL that reached the status
of a full ISO/IEC standard in 2008 [DSRL]. Unlike RELAX NG and
Schematron, DSRL is allowed to modify XML information set of the
validated document. While DSRL is primarily intended for renaming
XML elements and attributes, it can also define default values for
XML attributes and default contents for XML elements or subtrees so
that the default contents are inserted if they are missing in the
validated documents. The latter feature is used by the YANG-to-DSDL
mapping for representing YANG default contents consisting of leaf
nodes with default values and their ancestor non-presence containers.
DSRL elements are qualified with namespace URI
"http://purl.oclc.org/dsdl/dsrl".
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5. Additional Annotations
Besides the DSDL schema languages, the mapping also uses three sets
of annotations that are added as foreign-namespace attributes and
elements to RELAX NG schemas.
Two of the annotation sets - Dublin Core elements and DTD
compatibility annotations - are standard vocabularies for
representing metadata and documentation, respectively. Although
these data model items are not used for formal validation, they quite
often carry important information for data model implementers.
Therefore, they SHOULD be included in the hybrid schema and MAY also
appear in the final validation schemas.
The third set are NETMOD-specific annotations. They are specifically
designed for the hybrid schema and convey semantic constraints and
other information that cannot be expressed directly in RELAX NG. In
the second mapping step, these annotations are converted to
Schematron and DSRL rules.
5.1. Dublin Core Metadata Elements
Dublin Core is a system of metadata elements that was originally
created for describing metadata of World Wide Web resources in order
to facilitate their automated lookup. Later it was accepted as a
standard for describing metadata of arbitrary resources. This
specification uses the definition from [RFC5013].
Dublin Core elements are qualified with namespace URI
"http://purl.org/dc/terms".
5.2. RELAX NG DTD Compatibility Annotations
DTD compatibility annotations are a part of the RELAX NG DTD
Compatibility specification [RNG-DTD]. YANG-to-DSDL mapping uses
only the <a:documentation> annotation for representing YANG
'description' and 'reference' texts.
Note that there is no intention to make the resulting schemas DTD-
compatible, the main reason for using these annotations is technical:
they are well supported and adequately formatted by several RELAX NG
tools.
DTD compatibility annotations are qualified with namespace URI
"http://relaxng.org/ns/compatibility/annotations/1.0".
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5.3. NETMOD-Specific Annotations
NETMOD-specific annotations are XML elements and attributes qualified
with the namespace URI
"urn:ietf:params:xml:ns:netmod:dsdl-annotations:1" which appear in
various locations of the hybrid schema. YANG statements are mapped
to these annotations in a straightforward way. In most cases, the
annotation attributes and elements have the same name as the
corresponding YANG statement.
Table 2 lists alphabetically the names of NETMOD-specific annotation
attributes (prefixed with "@") and elements (in angle brackets) along
with a reference to the section where their use is described.
Appendix A contains a RELAX NG schema for this annotation vocabulary.
+---------------------------+--------------------+------+
| annotation | section | note |
+---------------------------+--------------------+------+
| @nma:config | 10.9 | |
| | | |
| <nma:data> | Section 8.1 | 4 |
| | | |
| @nma:default | 10.12 | |
| | | |
| <nma:error-app-tag> | 10.16 | 1 |
| | | |
| <nma:error-message> | 10.17 | 1 |
| | | |
| @nma:if-feature | 10.22 | |
| | | |
| @nma:implicit | 10.11, 10.7, 10.12 | |
| | | |
| <nma:input> | Section 8.1 | 4 |
| | | |
| <nma:instance-identifier> | 10.53.6 | 2 |
| | | |
| @nma:key | 10.26 | |
| | | |
| @nma:leaf-list | 10.28 | |
| | | |
| @nma:leafref | 10.53.7 | |
| | | |
| @nma:mandatory | 10.8 | |
| | | |
| @nma:max-elements | 10.28 | |
| | | |
| @nma:min-elements | 10.28 | |
| | | |
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| @nma:module | 10.34 | |
| | | |
| <nma:must> | 10.35 | 3 |
| | | |
| <nma:notification> | Section 8.1 | 4 |
| | | |
| <nma:notifications> | Section 8.1 | 4 |
| | | |
| @nma:ordered-by | 10.38 | |
| | | |
| <nma:output> | Section 8.1 | 4 |
| | | |
| <nma:rpc> | Section 8.1 | 4 |
| | | |
| <nma:rpcs> | Section 8.1 | 4 |
| | | |
| @nma:status | 10.51 | |
| | | |
| @nma:unique | 10.55 | |
| | | |
| @nma:units | 10.56 | |
| | | |
| @nma:when | 10.59 | |
+---------------------------+--------------------+------+
Table 2: NETMOD-specific annotations
Notes:
1. Appears only as a subelement of <nma:must>.
2. Has an optional attribute @require-instance.
3. Has a mandatory attribute @assert and two optional subelements
<nma:error-app-tag> and <nma:error-message>.
4. Marker element in the hybrid schema.
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6. Overview of the Mapping
This section gives an overview of the YANG-to-DSDL mapping, its
inputs and outputs. Figure 1 presents an overall structure of the
mapping:
+----------------+
| YANG module(s) |
+----------------+
|
|T
|
+------------------------------------+
| hybrid schema |
+------------------------------------+
/ | | \
/ | | \
Tg/ Tr| |Tn \
/ | | \
+---------+ +-----+ +-------+ +------+
|get reply| | rpc | | notif | | .... |
+---------+ +-----+ +-------+ +------+
Figure 1: Structure of the mapping
The mapping procedure is divided into two steps:
1. Transformation T in the first step maps one or more YANG modules
to the hybrid schema (see Section 8.1). Constraints that cannot
be expressed directly in RELAX NG (list key definitions, 'must'
statements etc.) and various documentation texts are recorded in
the schema as foreign-namespace annotations.
2. In the second step, the hybrid schema may be transformed in
multiple ways to a coordinated set of DSDL schemas that can be
used for validating a particular data object in a specific
context. Figure 1 shows three simple possibilities as examples.
In the process, appropriate parts of the hybrid schema are
extracted and specific annotations transformed to equivalent, but
usually more complex, Schematron patterns, DSRL element maps etc.
An implementation of the mapping algorithm MUST accept one or more
valid YANG modules as its input. It is important to be able to
process multiple YANG modules together since multiple modules may be
negotiated for a NETCONF session and the contents of the
configuration datastore is then obtained as the union of data trees
specified by the individual modules, which may also lead to multiple
root nodes of the datastore hierarchy. In addition, the input
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modules may be further coupled by the 'augment' statement in which
one module augments the data tree of another module.
It is also assumed that the algorithm has access, perhaps on demand,
to all YANG modules that the input modules import (directly or
transitively).
Other information contained in input YANG modules, such as semantic
constraints and default values, are recorded in the hybrid schema as
annotations - XML attributes or elements qualified with namespace URI
"urn:ietf:params:xml:ns:netmod:dsdl-annotations:1". Metadata
describing the YANG modules are mapped to Dublin Core annotations
elements (Section 5.1). Finally, documentation strings are mapped to
<a:documentation> elements belonging to the DTD compatibility
vocabulary (Section 5.2).
The output of the second step is a coordinated set of three DSDL
schemas corresponding to a specific data object and context:
o RELAX NG schema describing the grammatical and datatype
constraints;
o Schematron schema expressing other constraints such as uniqueness
of list keys or user-specified semantic rules;
o DSRL schema containing the specification of default contents.
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7. NETCONF Content Validation
This section describes how the schemas generated by the YANG-to-DSDL
mapping are supposed to be applied for validating XML instance
documents such as the contents of a datastore or various NETCONF
messages.
The validation proceeds in the following steps, which are also
illustrated in Figure 2:
1. The XML instance document is checked for grammatical and data
type validity using the RELAX NG schema.
2. Default values for leaf nodes have to be applied and their
ancestor containers added where necessary. It is important to
add the implicit nodes before the next validation step because
YANG specification [RFC6020] requires that the data tree against
which XPath expressions are evaluated already has all defaults
filled-in. Note that this step modifies the information set of
the validated XML document.
3. The semantic constraints are checked using the Schematron schema.
+----------+ +----------+
| | | XML |
| XML | | document |
| document |-----------o----------->| with |
| | ^ | defaults |
| | | | |
+----------+ | +----------+
^ | filling in ^
| grammar, | defaults | semantic
| datatypes | | constraints
| | |
+----------+ +--------+ +------------+
| RELAX NG | | DSRL | | Schematron |
| schema | | schema | | schema |
+----------+ +--------+ +------------+
Figure 2: Outline of the validation procedure
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8. Design Considerations
YANG data models could in principle be mapped to the DSDL schemas in
a number of ways. The mapping procedure described in this document
uses several specific design decisions that are discussed in the
following subsections.
8.1. Hybrid Schema
As was explained in Section 6, the first step of the mapping produces
an intermediate document - the hybrid schema, which specifies all
constraints for the entire data model in a single RELAX NG schema.
Every input YANG module corresponds to exactly one embedded grammar
in the hybrid schema. This separation of input YANG modules allows
each embedded grammar to include named pattern definitions into its
own namespace, which is important for mapping YANG groupings (see
Section 9.2 for additional details).
In addition to grammatical and datatype constraints, YANG modules
provide other important information that cannot be expressed in a
RELAX NG schema: semantic constraints, default values, metadata,
documentation and so on. Such information items are represented in
the hybrid schema as XML attributes and elements belonging to the
namespace with the following URI:
"urn:ietf:params:xml:ns:netmod:dsdl-annotations:1". A complete list
of these annotations is given in Section 5.3, detailed rules about
their use are then contained in the following sections.
YANG modules define data models not only for configuration and state
data but also for (multiple) RPC operations [RFC4741] and/or event
notifications [RFC5277]. In order to be able to capture all three
types of data models in one schema document, the hybrid schema uses
special markers that enclose sub-schemas for configuration and state
data, individual RPC operations (both input and output part) and
individual notifications.
The markers are the following XML elements in the namespace of
NETMOD-specific annotations (URI
urn:ietf:params:xml:ns:netmod:dsdl-annotations:1):
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+-------------------+---------------------------------------+
| Element name | Role |
+-------------------+---------------------------------------+
| nma:data | encloses configuration and state data |
| | |
| nma:rpcs | encloses all RPC operations |
| | |
| nma:rpc | encloses an individual RPC operation |
| | |
| nma:input | encloses an RPC request |
| | |
| nma:output | encloses an RPC reply |
| | |
| nma:notifications | encloses all notifications |
| | |
| nma:notification | encloses an individual notification |
+-------------------+---------------------------------------+
Table 3: Marker elements in the hybrid schema
For example, consider a data model formed by two YANG modules
"example-a" and "example-b" that define nodes in the namespaces
"http://example.com/ns/example-a" and
"http://example.com/ns/example-b". Module "example-a" defines
configuration/state data, RPC methods and notifications, whereas
"example-b" defines only configuration/state data. The hybrid schema
can then be schematically represented as follows:
<grammar xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
xmlns:exa="http://example.com/ns/example-a"
xmlns:exb="http://example.com/ns/example-b"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<start>
<grammar nma:module="example-a"
ns="http://example.com/ns/example-a">
<start>
<nma:data>
...configuration and state data defined in "example-a"...
</nma:data>
<nma:rpcs>
<nma:rpc>
<nma:input>
<element name="exa:myrpc">
...
</element>
</nma:input>
<nma:output>
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...
</nma:output>
</nma:rpc>
...
</nma:rpcs>
<nma:notifications>
<nma:notification>
<element name="exa:mynotif">
...
</element>
</nma:notification>
...
</nma:notifications>
</start>
...local named pattern definitions of example-a...
</grammar>
<grammar nma:module="example-b"
ns="http://example.com/ns/example-a">
<start>
<nma:data>
...configuration and state data defined in "example-b"...
</nma:data>
<nma:rpcs/>
<nma:notifications/>
</start>
...local named pattern definitions of example-b...
</grammar>
</start>
...global named pattern definitions...
</grammar>
A complete hybrid schema for the data model of a DHCP server is given
in Appendix C.2.
8.2. Modularity
Both YANG and RELAX NG offer means for modularity, i.e., for
splitting the contents of a full schema into separate modules and
combining or reusing them in various ways. However, the approaches
taken by YANG and RELAX NG differ. Modularity in RELAX NG is
suitable for ad hoc combinations of a small number of schemas whereas
YANG assumes a large set of modules similar to SNMP MIB modules. The
following differences are important:
o In YANG, whenever module A imports module B, it gets access to the
definitions (groupings and typedefs) appearing at the top level of
module B. However, no part of data tree from module B is imported
along with it. In contrast, the <rng:include> pattern in RELAX NG
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imports both definitions of named patterns and the entire schema
tree from the included schema.
o The names of imported YANG groupings and typedefs are qualified
with the namespace of the imported module. On the other hand, the
names of data nodes contained inside the imported groupings, when
used within the importing module, become part of the importing
module's namespace. In RELAX NG, the names of patterns are
unqualified and so named patterns defined in both the importing
and imported module share the same flat namespace. The contents
of RELAX NG named patterns may either keep the namespace of the
schema where they are defined or inherit the namespace of the
importing module, analogically to YANG. However, in order to
achieve the latter behavior, the definitions of named patterns
must be included from an external schema which has to be prepared
in a special way (see [Vli04], Chapter 11).
In order to map, as much as possible, the modularity of YANG to RELAX
NG, a validating RELAX NG schema (the result of the second mapping
step) has to be split into two files, one of them containing all
global definitions that are mapped from top-level YANG groupings
appearing in all input YANG module. This RELAX NG schema MUST NOT
define any namespace via the @ns attribute.
The other RELAX NG schema file then defines actual data trees mapped
from input YANG modules, each of them enclosed in an own embedded
grammar. Those embedded grammars in which at least one of the global
definitions is used MUST include the first schema with definitions
and also MUST define the local namespace using the @ns attribute.
This way, the global definitions can be used inside different
embedded grammar, each time accepting a different local namespace.
Named pattern definition that are mapped from non-top-level YANG
groupings MUST be placed inside the embedded grammar corresponding to
the YANG module where the grouping is defined.
In the hybrid schema, we need to distinguish the global and non-
global named pattern definitions while still keeping the hybrid
schema in one file. This is accomplished in the following way:
o Every global definition MUST be placed as a child of the the outer
<rng:grammar> element (the document root of the hybrid schema).
o Every non-global definitions MUST be placed as a child of the
corresponding embedded <rng:grammar> element.
YANG also allows for splitting a module into a number of submodules.
However, as submodules have no impact on the scope of identifiers and
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namespaces, the modularity based on submodules is not mapped in any
way. The contents of submodules is therefore handled as if the
submodule text appeared directly in the main module.
8.3. Granularity
RELAX NG supports different styles of schema structuring: One
extreme, often called "Russian Doll", specifies the structure of an
XML instance document in a single hierarchy. The other extreme, the
flat style, uses a similar approach as the Data Type Definition (DTD)
schema language - every XML element corresponds to a named pattern
definition. In practice, some compromise between the two extremes is
usually chosen.
YANG supports both styles in principle, too, but in most cases the
modules are organized in a way closer to the "Russian Doll" style,
which provides a better insight into the structure of the
configuration data. Groupings are usually defined only for contents
that are prepared for reuse in multiple places via the 'uses'
statement. In contrast, RELAX NG schemas tend to be much flatter,
because finer granularity is also needed in RELAX NG for
extensibility of the schemas - it is only possible to replace or
modify schema fragments that are factored out as named patterns. For
YANG this is not an issue since its 'augment' and 'refine' statements
can delve, by using path expressions, into arbitrary depths of
existing structures.
In general, it not feasible to map YANG's powerful extension
mechanisms to those available in RELAX NG. For this reason, the
mapping essentially keeps the granularity of the original YANG data
model: YANG groupings and definitions of derived types usually have
direct counterparts in definitions of named patterns in the resulting
RELAX NG schema.
8.4. Handling of XML Namespaces
Most modern XML schema languages, including RELAX NG, Schematron and
DSRL, support schemas for so-called compound XML documents which
contain elements from multiple namespaces. This is useful for our
purpose since the YANG-to-DSDL mapping allows for multiple input YANG
modules, which naturally leads to compound document schemas.
RELAX NG offers two alternatives for defining the target namespaces
in the schema:
1. First possibility is the traditional XML way via the @xmlns:xxx
attribute.
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2. One of the target namespace URIs may be declared using the @ns
attribute.
In both the hybrid schema and validation RELAX NG schemas generated
in the second step, the namespaces MUST be declared as follows:
1. The root <rng:grammar> MUST have @xmlns:xxx attributes declaring
prefixes of all namespaces that are used in the data model. The
prefixes SHOULD be identical to those defined in the 'prefix'
statements. An implementation of the mapping MUST resolve all
collisions in the prefixes defined by different input modules, if
there are any.
2. Each embedded <rng:grammar> element MUST declare the namespace of
the corresponding module using the @ns attribute. This way, the
names of nodes defined by global named patterns are able to adopt
the local namespace of each embedded grammar, as explained in
Section 8.2.
This setup is illustrated by the example at the end of Section 8.1.
DSRL schemas may declare any number of target namespaces via the
standard XML attributes xmlns:xxx.
In contrast, Schematron requires all used namespaces to be defined in
the <sch:ns> subelements of the document element <sch:schema>.
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9. Mapping YANG Data Models to the Hybrid Schema
This section explains the main principles governing the first step of
the mapping. Its result is the hybrid schema which is described in
Section 8.1.
A detailed specification of the mapping of individual YANG statements
is contained in the following Section 10.
9.1. Occurrence Rules for Data Nodes
In DSDL schema languages, occurrence constraints for a node are
always localized together with that node. In a RELAX NG schema, for
example, <rng:optional> pattern appears as the parent element of the
pattern defining a leaf or non-leaf element. Similarly, DSRL
specifies default contents separately for every single node, be it a
leaf or non-leaf element.
For leaf nodes in YANG modules, the occurrence constraints are also
easily inferred from the substatements of 'leaf'. On the other hand,
for a YANG container it is often necessary to examine its entire
subtree in order to determine the container's occurrence constraints.
Therefore, one of the goals of the first mapping step is to infer the
occurrence constraints for all data nodes and mark accordingly the
corresponding <rng:element> patterns in the hybrid schema so that any
transformation procedure in the second mapping step can simply use
this information and need not examine the subtree again.
First, it has to be decided whether a given data node must always be
present in a valid configuration. If so, such a node is called
mandatory, otherwise it is called optional. This constraint is
closely related to the notion of mandatory nodes in Section 3.1 in
[RFC6020]. The only difference is that this document also considers
list keys to be mandatory.
The other occurrence constraint has to do with the semantics of the
'default' statement and the possibility of removing empty non-
presence containers. As a result, the information set of a valid
configuration may be modified by adding or removing certain leaf or
container elements without changing the meaning of the configuration.
In this document, such elements are called implicit. In the hybrid
schema, they can be identified as RELAX NG patterns having either
@nma:default or @nma:implicit attribute.
Note that both occurrence constraints apply to containers at the top
level of the data tree, and then also to other containers under the
additional condition that their parent node exists in the instance
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document. For example, consider the following YANG fragment:
container outer {
presence 'Presence of "outer" means something.';
container c1 {
leaf foo {
type uint8;
default 1;
}
}
container c2 {
leaf-list bar {
type uint8;
min-elements 0;
}
}
container c3 {
leaf baz {
type uint8;
mandatory true;
}
}
}
Here, container "outer" has the 'presence' substatement, which means
that it is optional and not implicit. If "outer" is not present in a
configuration, its child containers are not present as well.
However, if "outer" does exist, it makes sense to ask which of its
child containers are optional and which are implicit. In this case,
"c1" is optional and implicit, "c2" is optional but not implicit and
"c3" is mandatory (and therefore not implicit).
The following subsections give precise rules for determining whether
a container is optional or mandatory and whether it is implicit. In
order to simplify the recursive definition of these occurrence
characteristics, it is useful to define them also for other types of
YANG schema nodes, i.e., leaf, list, leaf-list and anyxml and choice.
9.1.1. Optional and Mandatory Nodes
The decision whether a given node is mandatory or optional is
governed by the following rules:
o Leaf, anyxml and choice nodes are mandatory if they contain the
substatement "mandatory true;". For a choice node this means that
at least one node from exactly one case branch must exist.
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o In addition, a leaf node is mandatory if it is declared as a list
key.
o A list or leaf-list node is mandatory if it contains the 'min-
elements' substatement with an argument value greater than zero.
o A container node is mandatory if its definition does not contain
the 'presence' substatement and at least one of its child nodes is
mandatory.
A node which is not mandatory is said to be optional.
In RELAX NG, definitions of nodes that are optional must be
explicitly wrapped in the <rng:optional> element. The mapping MUST
use the above rules to determine whether a YANG node is optional and
if so, insert the <rng:optional> element in the hybrid schema.
However, alternatives in <rng:choice> MUST NOT be defined as optional
in the hybrid schema. If a choice in YANG is not mandatory, <rng:
optional> MUST be used to wrap the entire <rng:choice> pattern.
9.1.2. Implicit Nodes
The following rules are used to determine whether a given data node
is implicit:
o List, leaf-list and anyxml nodes are never implicit.
o A leaf node is implicit if and only if it has a default value,
defined either directly or via its datatype.
o A container node is implicit if and only if it does not have the
'presence' substatement, none of its children are mandatory and at
least one child is implicit.
In the hybrid schema, all implicit containers, as well as leafs that
obtain their default value from a typedef and don't have the @nma:
default attribute, MUST be marked with @nma:implicit attribute having
the value of "true".
Note that Section 7.9.3 in [RFC6020] specifies other rules that must
be taken into account when deciding whether a given container or leaf
appearing inside a case of a choice is ultimately implicit or not.
Specifically, a leaf or container under a case can be implicit only
if the case appears in the argument of the choice's 'default'
statement. However, this is not sufficient by itself but also
depends on the particular instance XML document, namely on the
presence or absence of nodes from other (non-default) cases. The
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details are explained in Section 11.3.
9.2. Mapping YANG Groupings and Typedefs
YANG groupings and typedefs are generally mapped to RELAX NG named
patterns. There are, however, several caveats that the mapping has
to take into account.
First of all, YANG typedefs and groupings may appear at all levels of
the module hierarchy and are subject to lexical scoping, see Section
5.5 in [RFC6020]. Second, top-level symbols from external modules
may be imported as qualified names represented using the external
module namespace prefix and the name of the symbol. In contrast,
named patterns in RELAX NG (both local and imported via the <rng:
include> pattern) share the same namespace and within a grammar they
are always global - their definitions may only appear at the top
level as children of the <rng:grammar> element. Consequently,
whenever YANG groupings and typedefs are mapped to RELAX NG named
pattern definitions, their names MUST be disambiguated in order to
avoid naming conflicts. The mapping uses the following procedure for
mangling the names of groupings and type definitions:
o Names of groupings and typedefs appearing at the top level of the
YANG module hierarchy are prefixed with the module name and two
underscore characters ("__").
o Names of other groupings and typedefs, i.e., those that do not
appear at the top level of a YANG module, are prefixed with the
module name, double underscore, and then the names of all ancestor
data nodes separated by double underscore.
o Finally, since the names of groupings and typedefs in YANG have
different namespaces, an additional underscore character is added
to the beginning of the mangled names of all groupings.
An additional complication is caused by the YANG rules for subelement
ordering (see, e.g., Section 7.5.7 in [RFC6020]): In RPC input and
output parameters, subelements must follow the order specified in the
data model, otherwise the order is arbitrary. Consequently, if a
grouping is used both in RPC input/output parameters and elsewhere,
it MUST be mapped to two different named pattern definitions - one
with fixed order and the other with arbitrary order. To distinguish
them, the "__rpc" suffix MUST be appended to the version with fixed
order.
EXAMPLE. Consider the following YANG module which imports the
standard module "ietf-inet-types" [RFC6021]:
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module example1 {
namespace "http://example.com/ns/example1";
prefix ex1;
typedef vowels {
type string {
pattern "[aeiouy]*";
}
}
grouping "grp1" {
leaf "void" {
type "empty";
}
}
container "cont" {
leaf foo {
type vowels;
}
uses "grp1";
}
}
The hybrid schema generated by the first mapping step will then
contain the following two (global) named pattern definitions:
<rng:define name="example1__vowels">
<rng:data type="string">
<rng:param name="pattern">[aeiouy]*</rng:param>
</rng:data>
</rng:define>
<rng:define name="_example1__grp1">
<rng:optional>
<rng:element name="void">
<rng:empty/>
</rng:element>
</rng:optional>
</rng:define>
9.2.1. YANG Refinements and Augments
YANG groupings represent a similar concept as named pattern
definitions in RELAX NG and both languages also offer mechanisms for
their subsequent modification. However, in RELAX NG the definitions
themselves are modified whereas YANG provides two substatements of
'uses' which modify expansions of groupings:
o 'refine' statement allows for changing parameters of a schema node
inside the grouping referenced by the parent 'uses' statement;
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o 'augment' statement can be used for adding new schema nodes to the
grouping contents.
Both 'refine' and 'augment' statements are quite powerful in that
they can address, using XPath-like expressions as their arguments,
schema nodes that are arbitrarily deep inside the grouping contents.
In contrast, modifications of named pattern definitions in RELAX NG
are applied exclusively at the topmost level of the named pattern
contents. In order to achieve a modifiability of named patterns
comparable to YANG, a RELAX NG schema would have to be extremely flat
(cf. Section 8.3) and very difficult to read.
Since the goal of the mapping described in this document is to
generate ad hoc DSDL schemas, we decided to avoid these complications
and instead expand the grouping and refine and/or augment it "in
place". In other words, every 'uses' statement which has 'refine'
and/or 'augment' substatements is replaced by the contents of the
corresponding grouping, the changes specified in the 'refine' and
'augment' statements are applied and the resulting YANG schema
fragment is mapped as if the 'uses'/'grouping' indirection wasn't
there.
If there are further 'uses' statements inside the grouping contents,
they may require expansion, too: it is necessary if the contained
'uses'/'grouping' pair lies on the "modification path" specified in
the argument of a 'refine' or 'augment' statement.
EXAMPLE. Consider the following YANG module:
module example2 {
namespace "http://example.com/ns/example2";
prefix ex2;
grouping leaves {
uses fr;
uses es;
}
grouping fr {
leaf feuille {
type string;
}
}
grouping es {
leaf hoja {
type string;
}
}
uses leaves;
}
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The resulting hybrid schema contains three global named pattern
definitions corresponding to the three groupings, namely
<rng:define name="_example2__leaves">
<rng:interleave>
<rng:ref name="_example2__fr"/>
<rng:ref name="_example2__es"/>
</rng:interleave>
</rng:define>
<rng:define name="_example2__fr">
<rng:optional>
<rng:element name="feuille">
<rng:data type="string"/>
</rng:element>
</rng:optional>
</rng:define>
<rng:define name="_example2__es">
<rng:optional>
<rng:element name="hoja">
<rng:data type="string"/>
</rng:element>
</rng:optional>
</rng:define>
and the configuration data part of the hybrid schema is a single
named pattern reference:
<nma:data>
<rng:ref name="_example2__leaves"/>
</nma:data>
Now assume that the "uses leaves" statement contains a 'refine'
substatement, for example:
uses leaves {
refine "hoja" {
default "alamo";
}
}
The resulting hybrid schema now contains just one named pattern
definition - "_example2__fr". The other two groupings "leaves" and
"es" have to be expanded because they both lie on the "modification
path", i.e., contain the leaf "hoja" that is being refined. The
configuration data part of the hybrid schema now looks like this:
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<nma:data>
<rng:interleave>
<rng:ref name="_example2__fr"/>
<rng:optional>
<rng:element name="ex2:hoja" nma:default="alamo">
<rng:data type="string"/>
</rng:element>
</rng:optional>
</rng:interleave>
</nma:data>
9.2.2. Type Derivation Chains
RELAX NG has no equivalent of the type derivation mechanism in YANG
that allows to restrict a built-in type (perhaps in multiple steps)
by adding new constraints. Whenever a derived YANG type is used
without restrictions - as a substatement of either 'leaf' or another
'typedef' - then the 'type' statement is mapped simply to a named
pattern reference <rng:ref>, and the type definition is mapped to a
RELAX NG named pattern definition <rng:define>. However, if any
restrictions are specified as substatements of the 'type' statement,
the type definition MUST be expanded at that point so that only the
ancestor built-in type appears in the hybrid schema, restricted with
facets that correspond to the combination of all restrictions found
along the type derivation chain and also in the 'type' statement.
EXAMPLE. Consider this YANG module:
module example3 {
namespace "http://example.com/ns/example3";
prefix ex3;
typedef dozen {
type uint8 {
range 1..12;
}
}
leaf month {
type dozen;
}
}
The 'type' statement in "leaf month" has no restrictions and is
therefore mapped simply to the reference <rng:ref
name="example3__dozen"/> and the corresponding named pattern is
defined as follows:
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<rng:define name="example3__dozen">
<rng:data type="unsignedByte">
<rng:param name="minInclusive">1</rng:param>
<rng:param name="maxInclusive">12</rng:param>
</rng:data>
</rng:define>
Assume now that the definition of leaf "month" is changed to
leaf month {
type dozen {
range 7..max;
}
}
The output RELAX NG schema then will not contain any named pattern
definition and the leaf "month" will be mapped directly to
<rng:element name="ex3:month">
<rng:data type="unsignedByte">
<rng:param name="minInclusive">7</rng:param>
<rng:param name="maxInclusive">12</rng:param>
</rng:data>
</rng:element>
The mapping of type derivation chains may be further complicated by
the presence of the 'default' statement in type definitions. In the
simple case, when a type definition containing the 'default'
statement is used without restrictions, the 'default' statement is
mapped to the @nma:default attribute attached to the <rng:define>
element.
However, if that type definition has to be expanded due to
restrictions, the @nma:default annotation arising from the expanded
type or ancestor types in the type derivation chain MUST be attached
to the pattern where the expansion occurs. If there are multiple
'default' statements in consecutive steps of the type derivation,
only the 'default' statement that is closest to the expanded type is
used.
EXAMPLE. Consider this variation of the last example:
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module example3bis {
namespace "http://example.com/ns/example3bis";
prefix ex3bis;
typedef dozen {
type uint8 {
range 1..12;
}
default 7;
}
leaf month {
type dozen;
}
}
The 'typedef' statement in this module is mapped to the following
named pattern definition:
<rng:define name="example3bis__dozen" @nma:default="7">
<rng:data type="unsignedByte">
<rng:param name="minInclusive">1</rng:param>
<rng:param name="maxInclusive">12</rng:param>
</rng:data>
</rng:define>
If the "dozen" type is restricted when used in the leaf "month"
definition as in the previous example, the "dozen" type has to be
expanded and @nma:default becomes an attribute of the <ex3bis:month>
element definition:
<rng:element name="ex3bis:month" @nma:default="7">
<rng:data type="unsignedByte">
<rng:param name="minInclusive">7</rng:param>
<rng:param name="maxInclusive">12</rng:param>
</rng:data>
</rng:element>
However, if the definition of the leaf "month" itself contained the
'default' substatement, the default specified for the "dozen" type
would be ignored.
9.3. Translation of XPath Expressions
YANG uses full XPath 1.0 syntax [XPath] for the arguments of 'must',
'when' and 'path' statements. As the names of data nodes defined in
a YANG module always belong to the namespace of that YANG module,
YANG adopted a simplification similar to the concept of default
namespace in XPath 2.0: node names in XPath expressions needn't carry
a namespace prefix inside the module where they are defined and the
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local module's namespace is assumed.
Consequently, all XPath expressions MUST be translated into a fully
conformant XPath 1.0 expression: Every unprefixed node name MUST be
prepended with the local module's namespace prefix as declared by the
'prefix' statement.
XPath expressions appearing inside top-level groupings require
special attention because all unprefixed node names contained in them
must adopt the namespace of each module where the grouping is used
(cf. Section 8.2. In order to achieve this, the local prefix MUST be
represented using the variable "$pref" in the hybrid schema. A
Schematron schema which encounters such an XPath expression then
supplies an appropriate value for this variable via a parameter to an
abstract pattern to which the YANG grouping is mapped (see
Section 11.2).
For example, XPath expression "/dhcp/max-lease-time" appearing in a
YANG module with the "dhcp" prefix will be translated to
o "$pref:dhcp/$pref:max-lease-time", if the expression is inside a
top-level grouping;
o "dhcp:dhcp/dhcp:max-lease-time", otherwise.
YANG also uses other XPath-like expressions, namely key identifiers
and "descendant schema node identifiers" (see the ABNF production for
and "descendant-schema-nodeid" in Section 12 of [RFC6020]). These
expressions MUST be translated by adding local module prefixes as
well.
9.4. YANG Language Extensions
YANG allows for extending its own language in-line by adding new
statements with keywords from special namespaces. Such extensions
first have to be declared using the 'extension' statement and then
they can be used as the standard YANG statements, from which they are
distinguished by a namespace prefix qualifying the extension keyword.
RELAX NG has a similar extension mechanism - XML elements and
attributes with names from foreign namespaces may be inserted at
almost any place of a RELAX NG schema.
YANG language extensions may or may not have a meaning in the context
of DSDL schemas. Therefore, an implementation MAY ignore any or all
of the extensions. However, an extension that is not ignored MUST be
mapped to XML element(s) and/or attribute(s) that exactly match the
YIN form of the extension, see Section 11.1 in [RFC6020].
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EXAMPLE. Consider the following extension defined by the "acme"
module:
extension documentation-flag {
argument number;
}
This extension can then be used in the same or another module, for
instance like this:
leaf folio {
acme:documentation-flag 42;
type string;
}
If this extension is honored by the mapping, it will be mapped to
<rng:element name="acme:folio">
<acme:documentation-flag number="42"/>
<rng:data type="string"/>
</rng:element>
Note that the 'extension' statement itself is not mapped in any way.
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10. Mapping YANG Statements to the Hybrid Schema
Each subsection in this section is devoted to one YANG statement and
provides the specification of how the statement is mapped to the
hybrid schema. The subsections are sorted alphabetically by the
statement keyword.
Each YANG statement is mapped to an XML fragment, typically a single
element or attribute but it may also be a larger structure. The
mapping procedure is inherently recursive, which means that after
finishing a statement the mapping continues with its substatements,
if there are any, and a certain element of the resulting fragment
becomes the parent of other fragments resulting from the mapping of
substatements. Any changes to this default recursive procedure are
explicitly specified.
YANG XML encoding rules translate to the following rules for ordering
multiple subelements:
1. Within the <nma:rpcs> subtree (i.e., for input and output
parameters of an RPC operation) the order of subelements is fixed
and their definitions in the hybrid schema MUST follow the order
specified in the source YANG module.
2. When mapping the 'list' statement, all keys MUST come before any
other subelements and in the same order as they are declared in
the 'key' statement. The order of the remaining (non-key)
subelements is not specified, so their definitions in the hybrid
schema MUST be enclosed in the <rng:interleave> element.
3. Otherwise, the order of subelements is arbitrary and,
consequently, all definitions of subelements in the hybrid schema
MUST be enclosed in the <rng:interleave> element.
The following conventions are used in this section:
o The argument of the statement being mapped is denoted by ARGUMENT.
o The element in the RELAX NG schema that becomes the parent of the
resulting XML fragment is denoted by PARENT.
10.1. The 'anyxml' Statement
This statement is mapped to <rng:element> element and ARGUMENT with
prepended local namespace prefix becomes the value of its @name
attribute. The contents of <rng:element> are
<rng:ref name="__anyxml__"/>
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Substatements of the 'anyxml' statement, if any, MAY be mapped to
additional children of the <rng:element> element.
If at least one 'anyxml' statement occurs in any of the input YANG
modules, the following pattern definition MUST be added exactly once
to the RELAX NG schema as a child of the root <rng:grammar> element
(cf. [Vli04], p. 172):
<rng:define name="__anyxml__">
<rng:zeroOrMore>
<rng:choice>
<rng:attribute>
<rng:anyName/>
</rng:attribute>
<rng:element>
<rng:anyName/>
<rng:ref name="__anyxml__"/>
</rng:element>
<rng:text/>
</rng:choice>
</rng:zeroOrMore>
</rng:define>
EXAMPLE: YANG statement in a module with namespace prefix "yam"
anyxml data {
description "Any XML content allowed here.";
}
is mapped to the following fragment:
<rng:element name="yam:data">
<a:documentation>Any XML content allowed here</a:documentation>
<rng:ref name="__anyxml__"/>
</rng:element>
An anyxml node is optional if there is no "mandatory true;"
substatement. The <rng:element> element then MUST be wrapped in
<rng:optional>, except when the 'anyxml' statement is a child of the
'choice' statement and thus forms a shorthand case for that choice
(see Section 9.1.1 for details).
10.2. The 'argument' Statement
This statement is not mapped to the output schema, but see the rules
for handling extensions in Section 9.4.
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10.3. The 'augment' Statement
As a substatement of 'uses', this statement is handled as a part of
'uses' mapping, see Section 10.57.
At the top level of a module or submodule, the 'augment' statement is
used for augmenting the schema tree of another YANG module. If the
augmented module is not processed within the same mapping session,
the top-level 'augment' statement MUST be ignored. Otherwise, the
contents of the statement are added to the foreign module with the
namespace of the module where the 'augment' statement appears.
10.4. The 'base' Statement
This statement is ignored as a substatement of 'identity' and handled
within the 'identityref' type if it appears as a substatement of that
type definition, see Section 10.53.5.
10.5. The 'belongs-to' Statement
This statement is not used since the processing of submodules is
always initiated from the main module, see Section 10.24.
10.6. The 'bit' Statement
This statement is handled within the "bits" type, see
Section 10.53.3.
10.7. The 'case' Statement
This statement is mapped to <rng:group> or <rng:interleave> element,
depending on whether the statement belongs to an definition of an RPC
operation or not. If the argument of a sibling 'default' statement
equals to ARGUMENT, @nma:implicit attribute with the value of "true"
MUST be added to that <rng:group> or <rng:interleave> element. The
@nma:implicit attribute MUST NOT be used for nodes at the top-level
of a non-default case (see Section 7.9.3 in [RFC6020]).
10.8. The 'choice' Statement
This statement is mapped to <rng:choice> element.
If 'choice' has the 'mandatory' substatement with the value of
"true", the attribute @nma:mandatory MUST be added to the <rng:
choice> element with the value of ARGUMENT. This case may require
additional handling, see Section 11.2.1. Otherwise, if "mandatory
true;" is not present, the <rng:choice> element MUST be wrapped in
<rng:optional>.
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The alternatives in <rng:choice> - mapped from either the 'case'
statement or a shorthand case - MUST NOT be defined as optional.
10.9. The 'config' Statement
This statement is mapped to @nma:config attribute and ARGUMENT
becomes its value.
10.10. The 'contact' Statement
This statement SHOULD NOT be used by the mapping since the hybrid
schema may be mapped from multiple YANG modules created by different
authors. The hybrid schema contains references to all input modules
in the Dublin Core elements <dc:source>, see Section 10.34. The
original YANG modules are the authoritative sources of the authorship
information.
10.11. The 'container' Statement
Using the rules specified in Section 9.1.1, the mapping algorithm
MUST determine whether the statement defines an optional container,
and if so, insert the <rng:optional> element and make it the new
PARENT.
The container defined by this statement is then mapped to the <rng:
element> element, which becomes a child of PARENT and uses ARGUMENT
with prepended local namespace prefix as the value of its @name
attribute.
Finally, using the rules specified in Section 9.1.2, the mapping
algorithm MUST determine whether the container is implicit, and if
so, add the attribute @nma:implicit with the value of "true" to the
<rng:element> element.
10.12. The 'default' Statement
If this statement is a substatement of 'leaf', it is mapped to the
@nma:default attribute of PARENT and ARGUMENT becomes its value.
As a substatement of 'typedef', the 'default' statement is also
mapped to the @nma:default attribute with the value of ARGUMENT. The
placement of this attribute depends on whether or not the type
definition has to be expanded when it is used:
o If the type definition is not expanded, @nma:default becomes an
attribute of the <rng:define> pattern resulting from the parent
'typedef' mapping.
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o Otherwise, @nma:default becomes an attribute of the ancestor RELAX
NG pattern inside which the expansion takes place.
Details and an example are given in Section 9.2.2.
Finally, as a substatement of 'choice', the 'default' statement
identifies the default case and is handled within the 'case'
statement, see Section 10.7. If the default case uses the shorthand
notation where the 'case' statement is omitted, the @nma:implicit
attribute with the value of "true" is either attached to the node
representing the default case in the shorthand notation or,
alternatively, an extra <rng:group> element MAY be inserted and the
@nma:implicit attribute attached to it. In the latter case, the net
result is the same as if the 'case' statement wasn't omitted for the
default case.
EXAMPLE. The following 'choice' statement in a module with namespace
prefix "yam"
choice leaves {
default feuille;
leaf feuille { type empty; }
leaf hoja { type empty; }
}
is either mapped directly to
<rng:choice>
<rng:element name="yam:feuille" nma:implicit="true">
<rng:empty/>
</rng:element>
<rng:element name="yam:hoja">
<rng:empty/>
</rng:element/>
</rng:choice>
or the default case may be wrapped in an extra <rng:group>:
<rng:choice>
<rng:group nma:implicit="true">
<rng:element name="yam:feuille">
<rng:empty/>
</rng:element>
</rng:group>
<rng:element name="yam:hoja">
<rng:empty/>
</rng:element/>
</rng:choice>
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10.13. The 'description' Statement
This statement is mapped to the DTD compatibility element
<a:documentation> and ARGUMENT becomes its text.
In order to get properly formatted in the RELAX NG compact syntax,
this element SHOULD be inserted as the first child of PARENT.
10.14. The 'deviation' Statement
This statement is ignored. However, it is assumed that all
deviations are known beforehand and the corresponding changes have
already been applied to the input YANG modules.
10.15. The 'enum' Statement
This statement is mapped to <rng:value> element and ARGUMENT becomes
its text. All substatements except 'status' are ignored because the
<rng:value> element cannot contain annotation elements, see [RNG],
section 6.
10.16. The 'error-app-tag' Statement
This statement is ignored unless it is a substatement of 'must'. In
the latter case it is mapped to the <nma:error-app-tag> element. See
also Section 10.35.
10.17. The 'error-message' Statement
This statement is ignored unless it is a substatement of 'must'. In
the latter case it is mapped to the <nma:error-message> element. See
also Section 10.35.
10.18. The 'extension' Statement
This statement is ignored. However, extensions to the YANG language
MAY be mapped as described in Section 9.4.
10.19. The 'feature' Statement
This statement is ignored.
10.20. The 'grouping' Statement
This statement is mapped to a RELAX NG named pattern definition <rng:
define>, but only if the grouping defined by this statement is used
without refinements and augments in at least one of the input
modules. In this case, the named pattern definition becomes a child
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of the <rng:grammar> element and its name is ARGUMENT mangled
according to the rules specified in Section 9.2.
As explained in Section 8.2, a named pattern definition MUST be
placed
o as a child of the root <rng:grammar> element if the corresponding
grouping is defined at the top level of an input YANG module;
o otherwise as a child of the embedded <rng:grammar> element
corresponding to the module in which the grouping is defined.
Whenever a grouping is used with refinements and/or augments, it is
expanded so that the refinements and augments may be applied in place
to the prescribed schema nodes. See Section 9.2.1 for further
details and an example.
An implementation MAY offer the option of mapping all 'grouping'
statements as named pattern definitions in the output RELAX NG schema
even if they are not referenced. This is useful for mapping YANG
"library" modules that typically contain only 'typedef' and/or
'grouping' statements.
10.21. The 'identity' Statement
This statement is mapped to the following named pattern definition
which is placed as a child of the root <rng:grammar> element:
<rng:define name="__PREFIX_ARGUMENT">
<rng:choice>
<rng:value type="QName">PREFIX:ARGUMENT</rng:value>
<rng:ref name="IDENTITY1"/>
...
</rng:choice>
</rng:define>
where
PREFIX is the prefix used in the hybrid schema for the namespace
of the module where the current identity is defined.
IDENTITY1 is the name of of the named pattern corresponding to an
identity which is derived from the current identity. Exactly one
<rng:ref> element MUST be present for every such identity.
EXAMPLE ([RFC6020], Section 7.16.3). The identities in the input
YANG modules
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module crypto-base {
namespace "http://example.com/crypto-base";
prefix "crypto";
identity crypto-alg {
description
"Base identity from which all crypto algorithms
are derived.";
}
}
module des {
namespace "http://example.com/des";
prefix "des";
import "crypto-base" {
prefix "crypto";
}
identity des {
base "crypto:crypto-alg";
description "DES crypto algorithm";
}
identity des3 {
base "crypto:crypto-alg";
description "Triple DES crypto algorithm";
}
}
will be mapped to the following named pattern definitions:
<define name="__crypto_crypto-alg">
<choice>
<value type="QName">crypto:crypto-alg</value>
<ref name="__des_des"/>
<ref name="__des_des3"/>
</choice>
</define>
<define name="__des_des">
<value type="QName">des:des</value>
</define>
<define name="__des_des3">
<value type="QName">des:des3</value>
</define>
10.22. The 'if-feature' Statement
ARGUMENT together with arguments of all sibling 'if-feature'
statements (with added prefixes, if missing) MUST be collected in a
space-separated list which becomes the value of the @nma:if-feature
attribute. This attribute is attached to PARENT.
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10.23. The 'import' Statement
This statement is not specifically mapped. The module whose name is
in ARGUMENT has to be parsed so that the importing module is able to
use its top-level groupings, typedefs and identities, and also
augment the data tree of the imported module.
If the 'import' statement has the 'revision' substatement, the
corresponding revision of the imported module MUST be used. The
mechanism for finding a given module revision is outside the scope of
this document.
10.24. The 'include' Statement
This statement is not specifically mapped. The submodule whose name
is in ARGUMENT has to be parsed and its contents mapped exactly as if
the submodule text appeared directly in the main module text.
If the 'include' statement has the 'revision' substatement, the
corresponding revision of the submodule MUST be used. The mechanism
for finding a given submodule revision is outside the scope of this
document.
10.25. The 'input' Statement
This statement is handled within 'rpc' statement, see Section 10.50.
10.26. The 'key' Statement
This statement is mapped to @nma:key attribute. ARGUMENT MUST be
translated so that every key is prefixed with the namespace prefix of
the local module. The result of this translation then becomes the
value of the @nma:key attribute.
10.27. The 'leaf' Statement
This statement is mapped to the <rng:element> element and ARGUMENT
with prepended local namespace prefix becomes the value of its @name
attribute.
If the leaf is optional, i.e., if there is no "mandatory true;"
substatement and the leaf is not declared among the keys of an
enclosing list, then the <rng:element> element MUST be enclosed in
<rng:optional>, except when the 'leaf' statement is a child of the
'choice' statement and thus represents a shorthand case for that
choice (see Section 9.1.1 for details).
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10.28. The 'leaf-list' Statement
This statement is mapped to a block enclosed by either <rng:
zeroOrMore> or <rng:oneOrMore> element depending on whether the
argument of 'min-elements' substatement is "0" or positive,
respectively (it is zero by default). This <rng:zeroOrMore> or <rng:
oneOrMore> element becomes the PARENT.
<rng:element> is then added as a child element of PARENT and ARGUMENT
with prepended local namespace prefix becomes the value of its @name
attribute. Another attribute, @nma:leaf-list, MUST also be added to
this <rng:element> element with the value of "true". If the 'leaf-
list' statement has the 'min-elements' substatement and its argument
is greater than one, additional attribute @nma:min-elements is
attached to <rng:element> and the argument of 'min-elements' becomes
the value of this attribute. Similarly, if there is the 'max-
elements' substatement and its argument value is not "unbounded",
attribute @nma:max-elements is attached to this element and the
argument of 'max-elements' becomes the value of this attribute.
EXAMPLE. A leaf-list appearing in a module with the namespace prefix
"yam"
leaf-list foliage {
min-elements 3;
max-elements 6378;
ordered-by user;
type string;
}
is mapped to the following RELAX NG fragment:
<rng:oneOrMore>
<rng:element name="yam:foliage" nma:leaf-list="true"
nma:ordered-by="user"
nma:min-elements="3" nma:max-elements="6378">
<rng:data type="string"/>
</rng:element>
</rng:oneOrMore>
10.29. The 'length' Statement
This statement is handled within the "string" type, see
Section 10.53.9.
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10.30. The 'list' Statement
This statement is mapped exactly as the 'leaf-list' statement, see
Section 10.28. The only difference is that the @nma:leaf-list
annotation either MUST NOT be present or MUST have the value of
"false".
When mapping the substatements of 'list', the order of children of
the list element MUST be specified so that list keys, if there are
any, always appear in the same order as they are defined in the 'key'
substatement and before other children, see [RFC6020], Section 7.8.5.
In particular, if a list key is defined in a grouping but the list
node itself is not a part of the same grouping, and the position of
the 'uses' statement would violate the above ordering requirement,
the grouping MUST be expanded, i.e., the 'uses' statement replaced by
the grouping contents.
For example, consider the following YANG fragment of a module with
the prefix "yam":
grouping keygrp {
leaf clef {
type uint8;
}
}
list foo {
key clef;
leaf bar {
type string;
}
leaf baz {
type string;
}
uses keygrp;
}
is mapped to the following RELAX NG fragment:
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<rng:zeroOrMore>
<rng:element name="yam:foo" nma:key="yam:clef">
<rng:element name="yam:clef">
<rng:data type="unsignedByte"/>
</rng:element>
<rng:interleave>
<rng:element name="yam:bar">
<rng:data type="string"/>
</rng:element>
<rng:element name="yam:baz">
<rng:data type="string"/>
</rng:element>
</rng:interleave>
</rng:element>
</rng:zeroOrMore>
Note that the "keygrp" grouping is expanded and the definition of
"yam:clef" is moved before the <rng:interleave> pattern.
10.31. The 'mandatory' Statement
This statement may appear as a substatement of 'leaf', 'choice' or
'anyxml' statement. If ARGUMENT is "true", the parent data node is
mapped as mandatory, see Section 9.1.1.
As a substatement of 'choice', this statement is also mapped to the
@nma:mandatory attribute which is added to PARENT. The value of this
attribute is the argument of the parent 'choice' statement.
10.32. The 'max-elements' Statement
This statement is handled within 'leaf-list' or 'list' statements,
see Section 10.28.
10.33. The 'min-elements' Statement
This statement is handled within 'leaf-list' or 'list' statements,
see Section 10.28.
10.34. The 'module' Statement
This statement is mapped to an embedded <rng:grammar> pattern having
the @nma:module attribute with the value of ARGUMENT. In addition, a
<dc:source> element SHOULD be created as a child of this <rng:
grammar> element and contain ARGUMENT as a metadata reference to the
input YANG module. See also Section 10.49.
Substatements of the 'module' statement MUST be mapped so that
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o statements representing configuration/state data are mapped to
descendants of the <nma:data> element;
o statements representing the contents of RPC requests or replies
are mapped to descendants of the <nma:rpcs> element;
o statements representing the contents of event notifications are
mapped to descendants of the <nma:notifications> element.
10.35. The 'must' Statement
This statement is mapped to the <nma:must> element. It has one
mandatory attribute @assert (with no namespace) which contains
ARGUMENT transformed into a valid XPath expression (see Section 9.3).
The <nma:must> element may have other subelements resulting from
mapping the 'error-app-tag' and 'error-message' substatements. Other
substatements of 'must', i.e., 'description' and 'reference', are
ignored.
EXAMPLE. YANG statement in the "dhcp" module
must 'current() <= ../max-lease-time' {
error-message
"The default-lease-time must be less than max-lease-time";
}
is mapped to
<nma:must assert="current()<=../dhcp:max-lease-time">
<nma:error-message>
The default-lease-time must be less than max-lease-time
</nma:error-message>
</nma:must>
10.36. The 'namespace' Statement
This statement is mapped in two ways:
1. To the @xmlns:PREFIX attribute of the root <rng:grammar> element
where PREFIX is the namespace prefix specified by the sibling
'prefix' statement. ARGUMENT becomes the value of this
attribute.
2. To the @ns attribute of PARENT, which is an embedded <rng:
grammar> pattern. ARGUMENT becomes the value of this attribute.
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10.37. The 'notification' Statement
This statement is mapped to the following subtree of the <nma:
notifications> element in the hybrid schema (where PREFIX is the
prefix of the local YANG module):
<nma:notification>
<rng:element name="PREFIX:ARGUMENT">
...
</rng:element>
</nma:notification>
Substatements of 'notification' are mapped under <rng:element
name="PREFIX:ARGUMENT">.
10.38. The 'ordered-by' Statement
This statement is mapped to @nma:ordered-by attribute and ARGUMENT
becomes the value of this attribute. See Section 10.28 for an
example.
10.39. The 'organization' Statement
This statement is ignored by the mapping because the hybrid schema
may be mapped from multiple YANG modules authored by different
parties. The hybrid schema SHOULD contain references to all input
modules in the Dublin Core <dc:source> elements, see Section 10.34.
The original YANG modules are the authoritative sources of the
authorship information.
10.40. The 'output' Statement
This statement is handled within the 'rpc' statement, see
Section 10.50.
10.41. The 'path' Statement
This statement is handled within the "leafref" type, see
Section 10.53.7.
10.42. The 'pattern' Statement
This statement is handled within the "string" type, see
Section 10.53.9.
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10.43. The 'position' Statement
This statement is ignored.
10.44. The 'prefix' Statement
This statement is handled within the sibling 'namespace' statement,
see Section 10.36, or within the parent 'import' statement, see
Section 10.23. As a substatement of 'belongs-to' (in submodules),
the 'prefix' statement is ignored.
10.45. The 'presence' Statement
This statement influences the mapping of the parent container
(Section 10.11): the parent container definition MUST be wrapped in
<rng:optional>, regardless of its contents. See also Section 9.1.1.
10.46. The 'range' Statement
This statement is handled within numeric types, see Section 10.53.8.
10.47. The 'reference' Statement
This statement is mapped to <a:documentation> element and its text is
set to ARGUMENT prefixed with "See: ".
10.48. The 'require-instance' Statement
This statement is handled within "instance-identifier" type
(Section 10.53.6).
10.49. The 'revision' Statement
The mapping uses only the most recent instance of the 'revision'
statement, i.e., one with the latest date in ARGUMENT, which
specifies the current revision of the input YANG module [RFC6020].
This date SHOULD be recorded, together with the name of the YANG
module, in the corresponding Dublin Core <dc:source> element (see
Section 10.34), for example in this form:
<dc:source>YANG module 'foo', revision 2010-03-02</dc:source>
The 'description' substatement of 'revision' is ignored.
10.50. The 'rpc' Statement
This statement is mapped to the following subtree in the RELAX NG
schema (where PREFIX is the prefix of the local YANG module):
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<nma:rpc>
<nma:input>
<rng:element name="PREFIX:ARGUMENT">
... mapped contents of 'input' ...
</rng:element>
</nma:input>
<nma:output">
... mapped contents of 'output' ...
</nma:output>
</nma:rpc>
As indicated in the schema fragment, contents of the 'input'
substatement (if any) are mapped under <rng:element name="PREFIX:
ARGUMENT">. Similarly, contents of the 'output' substatement are
mapped under <nma:output>. If there is no 'output' substatement, the
<nma:output> element MUST NOT be present.
The <nma:rpc> element is a child of <nma:rpcs>.
10.51. The 'status' Statement
This statement MAY be ignored. Otherwise, it is mapped to @nma:
status attribute and ARGUMENT becomes its value.
10.52. The 'submodule' Statement
This statement is not specifically mapped. Its substatements are
mapped as if they appeared directly in the module the submodule
belongs to.
10.53. The 'type' Statement
Most YANG built-in datatypes have an equivalent in the XSD datatype
library [XSD-D] as shown in Table 4.
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+-----------+---------------+--------------------------------+
| YANG type | XSD type | Meaning |
+-----------+---------------+--------------------------------+
| int8 | byte | 8-bit integer value |
| | | |
| int16 | short | 16-bit integer value |
| | | |
| int32 | int | 32-bit integer value |
| | | |
| int64 | long | 64-bit integer value |
| | | |
| uint8 | unsignedByte | 8-bit unsigned integer value |
| | | |
| uint16 | unsignedShort | 16-bit unsigned integer value |
| | | |
| uint32 | unsignedInt | 32-bit unsigned integer value |
| | | |
| uint64 | unsignedLong | 64-bit unsigned integer value |
| | | |
| string | string | character string |
| | | |
| boolean | boolean | "true" or "false" |
| | | |
| binary | base64Binary | binary data in base64 encoding |
+-----------+---------------+--------------------------------+
Table 4: YANG built-in datatypes with equivalents in the W3C XML
Schema Type Library
Two important datatypes of the XSD datatype library - "dateTime" and
"anyURI" - are not built-in types in YANG but instead are defined as
derived types in the standard modules [RFC6021]: "date-and-time" in
the "ietf-yang-types" module and "uri" in the "ietf-inet-types"
module. However, the formal restrictions in the YANG type
definitions are rather weak. Therefore, implementations of the YANG-
to-DSDL mapping SHOULD detect these derived types in source YANG
modules and map them to "dateType" and "anyURI", respectively.
Details about the mapping of individual YANG built-in types are given
in the following subsections.
10.53.1. The "empty" Type
This type is mapped to <rng:empty/>.
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10.53.2. The "boolean" and "binary" Types
These two built-in types do not allow any restrictions and are mapped
simply by inserting <rng:data> element whose @type attribute is set
to ARGUMENT mapped according to Table 4 above.
10.53.3. The "bits" Type
This type is mapped to <rng:list> and for each 'bit' substatement the
following XML fragment is inserted as a child of <rng:list>:
<rng:optional>
<rng:value>bit_name</rng:value>
</rng:optional>
where bit_name is the name of the bit as found in the argument of a
'bit' substatement.
10.53.4. The "enumeration" and "union" Types
These types are mapped to the <rng:choice> element.
10.53.5. The "identityref" Type
This type is mapped to the following named pattern reference:
<rng:ref name="__PREFIX_BASE"/>
where PREFIX:BASE is the qualified name of the identity appearing in
the argument of the 'base' substatement.
For example, assume that module "des" in Section 10.21 contains the
following leaf definition:
leaf foo {
type identityref {
base crypto:crypto-alg;
}
}
This leaf would then be mapped to the following element pattern:
<element name="des:foo">
<ref name="__crypto_crypto-alg"/>
</element>
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10.53.6. The "instance-identifier" Type
This type is mapped to <rng:data> element with @type attribute set to
"string". In addition, an empty <nma:instance-identifier> element
MUST be inserted as a child of PARENT.
The argument of the 'require-instance' substatement, if it exists,
becomes the value of the @require-instance attribute of the <nma:
instance-identifier> element.
10.53.7. The "leafref" Type
This type is mapped exactly as the type of the leaf given in the
argument of 'path' substatement. However, if the type of the
referred leaf defines a default value, this default value MUST be
ignored by the mapping.
In addition, @nma:leafref attribute MUST be added to PARENT. The
argument of the 'path' substatement, translated according to
Section 9.3, is set as the value of this attribute.
10.53.8. The Numeric Types
YANG built-in numeric types are "int8", "int16", "int32", "int64",
"uint8", "uint16", "uint32", "uint64" and "decimal64". They are
mapped to <rng:data> element with @type attribute set to ARGUMENT
translated according to Table 4 above.
An exception is the "decimal64" type, which is mapped to the
"decimal" type of the XSD datatype library. Its precision and number
of fractional digits are controlled with the following facets, which
MUST always be present:
o "totalDigits" facet set to the value of 19.
o "fractionDigits" facet set to the argument of the 'fraction-
digits' substatement.
The fixed value of "totalDigits" corresponds to the maximum of 19
decimal digits for 64-bit integers.
For example, the statement
type decimal64 {
fraction-digits 2;
}
is mapped to the following RELAX NG datatype:
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<rng:data type="decimal">
<rng:param name="totalDigits">19</rng:param>
<rng:param name="fractionDigits">2</rng:param>
</rng:data>
All numeric types support the 'range' restriction, which is mapped as
follows:
If the range expression consists of just a single range LO..HI, then
it is mapped to a pair of datatype facets
<rng:param name="minInclusive">LO</rng:param>
and
<rng:param name="maxInclusive">HI</rng:param>
If the range consists of a single number, the values of both facets
are set to this value. If LO is equal to the string "min", the
"minInclusive" facet is omitted. If HI is equal to the string "max",
the "maxInclusive" facet is omitted.
If the range expression has multiple parts separated by "|", then the
parent <rng:data> element must be repeated once for every range part
and all such <rng:data> elements are wrapped in <rng:choice> element.
Each <rng:data> element contains the "minInclusive" and
"maxInclusive" facets for one part of the range expression as
described in the previous paragraph.
For the "decimal64" type, the "totalDigits" and "fractionDigits" must
be repeated inside each of the <rng:data> elements.
For example,
type int32 {
range "-6378..0|42|100..max";
}
is mapped to the following RELAX NG fragment:
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<rng:choice>
<rng:data type="int">
<rng:param name="minInclusive">-6378</rng:param>
<rng:param name="maxInclusive">0</rng:param>
</rng:data>
<rng:data type="int">
<rng:param name="minInclusive">42</rng:param>
<rng:param name="maxInclusive">42</rng:param>
</rng:data>
<rng:data type="int">
<rng:param name="minInclusive">100</rng:param>
</rng:data>
</rng:choice>
See Section 9.2.2 for further details on mapping the restrictions.
10.53.9. The "string" Type
This type is mapped to <rng:data> element with the @type attribute
set to "string".
The 'length' restriction is handled analogically to the 'range'
restriction for the numeric types (Section 10.53.8):
If the length expression has just a single range, then
o if the length range consists of a single number LENGTH, the
following datatype facet is inserted:
<rng:param name="length">LENGTH</rng:param>.
o Otherwise the length range is of the form LO..HI, i.e., it
consists of both the lower and upper bound. The following two
datatype facets are then inserted:
<rng:param name="minLength">LO</rng:param>
and
<rng:param name="maxLength">HI</rng:param>
If LO is equal to the string "min", the "minLength" facet is
omitted. If HI is equal to the string "max", the "maxLength"
facet is omitted.
If the length expression has of multiple parts separated by "|", then
the parent <rng:data> element must be repeated once for every range
part and all such <rng:data> elements are wrapped in <rng:choice>
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element. Each <rng:data> element contains the "length" or
"minLength" and "maxLength" facets for one part of the length
expression as described in the previous paragraph.
Every 'pattern' restriction of the "string" datatype is mapped to the
"pattern" facet
<rng:param name="pattern">...</rng:param>
with text equal to the argument of the 'pattern' statement. All such
"pattern" facets must be repeated inside each copy of the <rng:data>
element, i.e., once for each length range.
For example,
type string {
length "1|3..8";
pattern "[A-Z][a-z]*";
}
is mapped to the following RELAX NG fragment:
<rng:choice>
<rng:data type="string">
<rng:param name="length">1</rng:param>
<rng:param name="pattern">[A-Z][a-z]*</rng:param>
</rng:data>
<rng:data type="string">
<rng:param name="minLength">3</rng:param>
<rng:param name="maxLength">8</rng:param>
<rng:param name="pattern">[A-Z][a-z]*</rng:param>
</rng:data>
</rng:choice>
10.53.10. Derived Types
If the 'type' statement refers to a derived type, it is mapped in one
of the following ways depending on whether it contains any
restrictions as its substatements:
1. Without restrictions, the 'type' statement is mapped simply to
the <rng:ref> element, i.e., a reference to a named pattern. If
the RELAX NG definition of this named pattern has not been added
to the hybrid schema yet, the corresponding type definition MUST
be found and its mapping installed as a subelement of either the
root or an embedded <rng:grammar> element, see Section 10.54.
Even if a given derived type is used more than once in the input
YANG modules, the mapping of the corresponding 'typedef' MUST be
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installed only once.
2. If any restrictions are present, the ancestor built-in type for
the given derived type must be determined and the mapping of this
base type MUST be used. Restrictions appearing at all stages of
the type derivation chain MUST be taken into account and their
conjunction added to the <rng:data> element which defines the
basic type.
See Section 9.2.2 for more details and an example.
10.54. The 'typedef' Statement
This statement is mapped to a RELAX NG named pattern definition <rng:
define>, but only if the type defined by this statement is used
without restrictions in at least one of the input modules. In this
case, the named pattern definition becomes a child of either the root
or an embedded <rng:grammar> element, depending on whether the
'typedef' statement appears at the top level of a YANG module or not.
The name of this named pattern definition is set to ARGUMENT mangled
according to the rules specified in Section 9.2.
Whenever a derived type is used with additional restrictions, the
ancestor built-in type for the derived type is used instead with
restrictions (facets) that are a combination of all restrictions
specified along the type derivation chain. See Section 10.53.10 for
further details and an example.
An implementation MAY offer the option of recording all 'typedef'
statements as named patterns in the output RELAX NG schema even if
they are not referenced. This is useful for mapping YANG "library"
modules containing only 'typedef' and/or 'grouping' statements.
10.55. The 'unique' Statement
This statement is mapped to @nma:unique attribute. ARGUMENT MUST be
translated so that every node identifier in each of its components is
prefixed with the namespace prefix of the local module, unless the
prefix is already present. The result of this translation then
becomes the value of the @nma:unique attribute.
For example, assuming that the local module prefix is "ex",
unique "foo ex:bar/baz"
is mapped to the following attribute/value pair:
nma:unique="ex:foo ex:bar/ex:baz"
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10.56. The 'units' Statement
This statement is mapped to @nma:units attribute and ARGUMENT becomes
its value.
10.57. The 'uses' Statement
If this statement has neither 'refine' nor 'augment' substatements,
it is mapped to <rng:ref> element, i.e., a reference to a named
pattern, and the value of its @name attribute is set to ARGUMENT
mangled according to Section 9.2. If the RELAX NG definition of the
referenced named pattern has not been added to the hybrid schema yet,
the corresponding grouping MUST be found and its mapping installed as
a subelement of <rng:grammar>, see Section 10.20.
Otherwise, if the 'uses' statement has any 'refine' or 'augment'
substatements, the corresponding grouping must be looked up and its
contents inserted under PARENT. See Section 9.2.1 for further
details and an example.
10.58. The 'value' Statement
This statement is ignored.
10.59. The 'when' Statement
This statement is mapped to @nma:when attribute and ARGUMENT,
translated according to Section 9.3, becomes it value.
10.60. The 'yang-version' Statement
This statement is not mapped to the output schema. However, an
implementation SHOULD check that it is compatible with the YANG
version declared by the statement (currently version 1). In the case
of a mismatch, the implementation SHOULD report an error and
terminate.
10.61. The 'yin-element' Statement
This statement is not mapped to the output schema, but see the rules
for extension handling in Section 9.4.
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11. Mapping the Hybrid Schema to DSDL
As explained in Section 6, the second step of the YANG-to-DSDL
mapping takes the hybrid schema and transforms it to various DSDL
schemas capable of validating instance XML documents. As an input
parameter, this step takes, in the simplest case, just a
specification of the NETCONF XML document type that is to be
validated. These document types can be, for example, the contents of
a datastore, a reply to <nc:get> or <nc:get-config>, contents of
other RPC requests/replies and event notifications, and so on.
The second mapping step has to accomplish the following three general
tasks:
1. Extract the parts of the hybrid schema that are appropriate for
the requested document type. For example, if a <nc:get> reply is
to be validated, the subtree under <nma:data> has to be selected.
2. The schema must be adapted to the specific encapsulating XML
elements mandated by the RPC layer. These are, for example, <nc:
rpc> and <nc:data> elements in the case of a <nc:get> reply or
<en:notification> for a notification.
3. Finally, NETMOD-specific annotations that are relevant for the
schema language of the generated schema must be mapped to the
corresponding patterns or rules.
These three tasks are together much simpler than the first mapping
step and can be effectively implemented using XSL transformations
[XSLT].
The following subsections describe the details of the second mapping
step for the individual DSDL schema languages. Section 12 then
contains a detailed specification for the mapping of all NETMOD-
specific annotations.
11.1. Generating RELAX NG Schemas for Various Document Types
With one minor exception, obtaining a validating RELAX NG schema from
the hybrid schema only means taking appropriate parts of the hybrid
schema and assembling them in a new RELAX NG grammar, perhaps after
removing all unwanted annotations.
The structure of the resulting RELAX NG schema is similar to that of
the hybrid schema: The root grammar contains embedded grammars, one
for each input YANG module. However, as explained in Section 8.2,
global named pattern definitions (children of the root <rng:grammar>
element) MUST be moved to a separate schema file.
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Depending on the XML document type that is the target for validation,
such as <nc:get>/<nc:get-config> reply, RPC operations or
notifications, patterns defining corresponding top-level information
items MUST be added, such as <nc:rpc-reply> with the @message-id
attribute and so on.
In order to avoid copying common named pattern definitions for common
NETCONF elements and attributes to every single output RELAX NG file,
such schema-independent definitions SHOULD be collected in a library
file which is then included by the validating RELAX NG schemas.
Appendix B has the listing of such a library file.
The minor exception mentioned above is the annotation @nma:config,
which must be observed if the target document type is a reply to <nc:
get-config>. In this case, each element definition that has this
attribute with the value of "false" MUST be removed from the schema
together with its descendants. See Section 12.1 for more details.
11.2. Mapping Semantic Constraints to Schematron
Schematron schemas tend to be much flatter and more uniform compared
to RELAX NG. They have exactly four levels of XML hierarchy: <sch:
schema>, <sch:pattern>, <sch:rule> and <sch:assert> or <sch:report>.
In a Schematron schema generated by the second mapping step, the
basic unit of organization is a rule represented by the <sch:rule>
element. The following NETMOD-specific annotations from the hybrid
schema (henceforth called "semantic annotations") are mapped to
corresponding Schematron rules: <nma:must>, @nma:key, @nma:unique,
@nma:max-elements, @nma:min-elements, @nma:when, @nma:leafref, @nma:
leaf-list, and also @nma:mandatory appearing as an attribute of <rng:
choice> (see Section 11.2.1).
Each input YANG module is mapped to a Schematron pattern whose @id
attribute is set to the module name. Every <rng:element> pattern
containing at least one of the above-mentioned semantic annotations
is then mapped to a Schematron rule:
<sch:rule context="XELEM">
...
</sch:rule>
The value of the mandatory @context attribute of <sch:rule> (denoted
as XELEM) MUST be set to the absolute path of the context element in
the data tree. The <sch:rule> element contains the mappings of all
contained semantic annotations in the form of Schematron asserts or
reports.
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Semantic annotations appearing inside a named pattern definition
(i.e., having <rng:define> among its ancestors) require special
treatment because they may be potentially used in different contexts.
This is accomplished by using Schematron abstract patterns that use
the "$pref" variable in place of the local namespace prefix. The
value of the @id attribute of such an abstract pattern MUST be set to
the name of the named pattern definition which is being mapped (i.e.,
the mangled name of the original YANG grouping).
When the abstract pattern is instantiated, the values of the
following two parameters MUST be provided:
o pref: the actual namespace prefix,
o start: XPath expression defining the context in which the grouping
is used.
EXAMPLE. Consider the following YANG module:
module example4 {
namespace "http://example.com/ns/example4";
prefix ex4;
uses sorted-leaf-list;
grouping sorted-leaf-list {
leaf-list sorted-entry {
must "not(preceding-sibling::sorted-entry > .)" {
error-message "Entries must appear in ascending order.";
}
type uint8;
}
}
}
The resulting Schematron schema for a reply to <nc:get> is then as
follows:
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<?xml version="1.0" encoding="utf-8"?>
<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron">
<sch:ns uri="http://example.com/ns/example4" prefix="ex4"/>
<sch:ns uri="urn:ietf:params:xml:ns:netconf:base:1.0"
prefix="nc"/>
<sch:pattern abstract="true"
id="_example4__sorted-leaf-list">
<sch:rule context="$start/$pref:sorted-entry">
<sch:report
test=". = preceding-sibling::$pref:sorted-entry">
Duplicate leaf-list entry "<sch:value-of select="."/>".
</sch:report>
<sch:assert
test="not(preceding-sibling::$pref:sorted-entry > .)">
Entries must appear in ascending order.
</sch:assert>
</sch:rule>
</sch:pattern>
<sch:pattern id="example4"/>
<sch:pattern id="id2573371" is-a="_example4__sorted-leaf-list">
<sch:param name="start" value="/nc:rpc-reply/nc:data"/>
<sch:param name="pref" value="ex4"/>
</sch:pattern>
</sch:schema>
The "sorted-leaf-list" grouping from the input module is mapped to an
abstract pattern with an @id value of "_example4__sorted-leaf-list"
in which the 'must' statement corresponds to the <sch:assert>
element. The abstract pattern is the instantiated by the pattern
with an @id value of "id2802112" which sets the "start" and "pref"
parameters to appropriate values.
Note that another Schematron element, <sch:report>, was automatically
added, checking for duplicate leaf-list entries.
The mapping from the hybrid schema to Schematron proceeds in the
following steps:
1. First, the active subtree(s) of the hybrid schema must be
selected depending on the requested target document type. This
procedure is identical to the RELAX NG case, including the
handling of @nma:config if the target document type is <nc:get-
config> reply.
2. Namespaces of all input YANG modules, together with the
namespaces of base NETCONF ("nc" prefix) or notifications ("en"
prefix) MUST be declared using the <sch:ns> element, for example
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<sch:ns uri="http://example.com/ns/example4" prefix="ex4"/>
3. One pattern is created for every input module. In addition, an
abstract pattern is created for every named pattern definition
containing one or more semantic annotations.
4. A <sch:rule> element is created for each element pattern
containing semantic annotations.
5. Every such annotation is then mapped to an <sch:assert> or <sch:
report> element which is installed as a child of the <sch:rule>
element.
11.2.1. Constraints on Mandatory Choice
In order to fully represent the semantics of YANG's 'choice'
statement with the "mandatory true;" substatement, the RELAX NG
grammar has to be combined with a special Schematron rule.
EXAMPLE. Consider the following module:
module example5 {
namespace "http://example.com/ns/example5";
prefix ex5;
choice foobar {
mandatory true;
case foo {
leaf foo1 {
type uint8;
}
leaf foo2 {
type uint8;
}
}
leaf bar {
type uint8;
}
}
}
In this module, all three leaf nodes in both case branches are
optional but because of the "mandatory true;" statement, at least one
of them must be present in a valid configuration. The 'choice'
statement from this module is mapped to the following fragment of the
RELAX NG schema:
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<rng:choice>
<rng:interleave>
<rng:optional>
<rng:element name="ex5:foo1">
<rng:data type="unsignedByte"/>
</rng:element>
</rng:optional>
<rng:optional>
<rng:element name="ex5:foo2">
<rng:data type="unsignedByte"/>
</rng:element>
</rng:optional>
</rng:interleave>
<rng:element name="ex5:bar">
<rng:data type="unsignedByte"/>
</rng:element>
</rng:choice>
In the second case branch, the "ex5:bar" element is defined as
mandatory so that this element must be present in a valid
configuration if this branch is selected. However, the two elements
in the first branch "foo" cannot be both declared as mandatory since
each of them alone suffices for a valid configuration. As a result,
the above RELAX NG fragment would successfully validate
configurations where none of the three leaf elements are present.
Therefore, mandatory choices, which can be recognized in the hybrid
schema as <rng:choice> elements with the @nma:mandatory annotation,
have to be handled in a special way: For each mandatory choice where
at least one of the cases contains more than one node, a Schematron
rule MUST be added enforcing the presence of at least one element
from any of the cases. (RELAX NG schema guarantees that elements
from different cases cannot be mixed together, that all mandatory
nodes are present etc.).
For the example module above, the Schematron rule will be as follows:
<sch:rule context="/nc:rpc-reply/nc:data">
<sch:assert test="ex5:foo1 or ex5:foo2 or ex5:bar">
Node(s) from at least one case of choice "foobar" must exist.
</sch:assert>
</sch:rule>
11.3. Mapping Default Values to DSRL
DSRL is the only component of DSDL which is allowed to change the
information set of the validated XML document. While DSRL also has
other functions, YANG-to-DSDL mapping uses it only for specifying and
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applying default contents. For XML instance documents based on YANG
data models, insertion of default contents may potentially take place
for all implicit nodes identified by the rules in Section 9.1.2.
In DSRL, the default contents of an element are specified using the
<dsrl:default-content> element, which is a child of <dsrl:element-
map>. Two sibling elements of <dsrl:default-content> determine the
context for the application of the default contents, see [DSRL]:
o <dsrl:parent> element contains an XSLT pattern specifying the
parent element; the default contents are applied only if the
parent element exists in the instance document.
o <dsrl:name> contains the XML name of the element which, if missing
or empty, is inserted together with the contents of <dsrl:default-
content>.
The <dsrl:parent> element is optional in a general DSRL schema but,
for the purpose of the YANG-to-DSDL mapping, this element MUST be
always present, in order to guarantee a proper application of default
contents.
DSRL mapping only deals with <rng:element> patterns in the hybrid
schema that define implicit nodes (see Section 9.1.2). Such element
patterns are distinguished by having NETMOD-specific annotation
attributes @nma:default or @nma:implicit, i.e., either
<rng:element name="ELEM" nma:default="DEFVALUE">
...
</rng:element>
or
<rng:element name="ELEM" nma:implicit="true">
...
</rng:element>
The former case applies to leaf nodes having the 'default'
substatement, but also to leaf nodes that obtain their default value
from a typedef, if this typedef is expanded according to the rules in
Section 9.2.2 so that the @nma:default annotation is attached
directly to the leaf's element pattern.
The latter case is used for all implicit containers (see Section 9.1)
and for leafs that obtain the default value from a typedef and don't
have the @nma:default annotation.
In the simplest case, both element patterns are mapped to the
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following DSRL element map:
<dsrl:element-map>
<dsrl:parent>XPARENT</dsrl:parent>
<dsrl:name>ELEM</dsrl:name>
<dsrl:default-content>DEFCONT</dsrl:default-content>
</dsrl:element-map>
where XPARENT is the absolute XPath of ELEM's parent element in the
data tree and DEFCONT is constructed as follows:
o If the implicit node ELEM is a leaf and has the @nma:default
attribute, DEFCONT is set to the value of this attribute (denoted
above as DEFVALUE).
o If the implicit node ELEM is a leaf and has the @nma:implicit
attribute with the value of "true", the default value has to be
determined from the @nma:default attribute of the definition of
ELEM's type (perhaps recursively) and used in place of DEFCONT in
the above DSRL element map. See also Section 9.2.2.
o Otherwise, the implicit node ELEM is a container and DEFCONT is
constructed as an XML fragment containing all descendant elements
of ELEM that have either @nma:implicit or @nma:default attribute.
In addition, when mapping the default case of a choice, it has to be
guaranteed that the default contents are not applied if any node from
any non-default case is present. This is accomplished by setting
<dsrl:parent> in a special way:
<dsrl:parent>XPARENT[not (ELEM1|ELEM2|...|ELEMn)]</dsrl:parent>
where ELEM1, ELEM2, ... ELEMn are the names of all top-level nodes
from all non-default cases. The rest of the element map is exactly
as before.
EXAMPLE. Consider the following YANG module:
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module example6 {
namespace "http://example.com/ns/example6";
prefix ex6;
container outer {
leaf leaf1 {
type uint8;
default 1;
}
choice one-or-two {
default "one";
container one {
leaf leaf2 {
type uint8;
default 2;
}
}
leaf leaf3 {
type uint8;
default 3;
}
}
}
}
The DSRL schema generated for the "get-reply" target document type
will be:
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<?xml version="1.0" encoding="utf-8"?>
<dsrl:maps xmlns:dsrl="http://purl.oclc.org/dsdl/dsrl"
xmlns:ex6="http://example.com/ns/example6"
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data</dsrl:parent>
<dsrl:name>ex6:outer</dsrl:name>
<dsrl:default-content>
<ex6:leaf1>1</ex6:leaf1>
<ex6:one><ex6:leaf2>2</ex6:leaf2></ex6:one>
<?xml version="1.0" encoding="utf-8"?>
<dsrl:maps xmlns:dsrl="http://purl.oclc.org/dsdl/dsrl"
xmlns:ex6="http://example.com/ns/example6"
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data</dsrl:parent>
<dsrl:name>ex6:outer</dsrl:name>
<dsrl:default-content>
<ex6:leaf1>1</ex6:leaf1>
<ex6:one>
<ex6:leaf2>2</ex6:leaf2>
</ex6:one>
</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data/ex6:outer</dsrl:parent>
<dsrl:name>ex6:leaf1</dsrl:name>
<dsrl:default-content>1</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>
/nc:rpc-reply/nc:data/ex6:outer[not(ex6:leaf3)]
</dsrl:parent>
<dsrl:name>ex6:one</dsrl:name>
<dsrl:default-content>
<ex6:leaf2>2</ex6:leaf2>
</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>
/nc:rpc-reply/nc:data/ex6:outer/ex6:one
</dsrl:parent>
<dsrl:name>ex6:leaf2</dsrl:name>
<dsrl:default-content>2</dsrl:default-content>
</dsrl:element-map>
</dsrl:maps>
Note that the default value for "leaf3" defined in the YANG module is
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ignored because "leaf3" represents a non-default alternative of a
choice and as such never becomes an implicit element.
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12. Mapping NETMOD-specific Annotations to DSDL Schema Languages
This section contains the mapping specification for the individual
NETMOD-specific annotations. In each case, the result of the mapping
must be inserted into an appropriate context of the target DSDL
schema as described in Section 11. The context is determined by the
element pattern in the hybrid schema to which the annotation is
attached. In the rest of this section, CONTELEM will denote the name
of this context element properly qualified with its namespace prefix.
12.1. The @nma:config Annotation
If this annotation is present with the value of "false", the
following rules MUST be observed for DSDL schemas of <nc:get-config>
reply:
o When generating RELAX NG, the contents of the CONTELEM definition
MUST be changed to <rng:notAllowed>.
o When generating Schematron or DSRL, the CONTELEM definition and
all its descendants in the hybrid schema MUST be ignored.
12.2. The @nma:default Annotation
This annotation is used for generating the DSRL schema as described
in Section 11.3.
12.3. The <nma:error-app-tag> Annotation
This annotation currently has no mapping defined.
12.4. The <nma:error-message> Annotation
This annotation is handled within <nma:must>, see Section 12.13.
12.5. The @if-feature Annotation
The information about available features MAY be supplied as an input
parameter to an implementation. In this case, the following changes
MUST be performed for all features that are considered unavailable:
o When generating RELAX NG, the contents of the CONTELEM definition
MUST be changed to <rng:notAllowed>.
o When generating Schematron or DSRL, the CONTELEM definition and
all its descendants in the hybrid schema MUST be ignored.
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12.6. The @nma:implicit Annotation
This annotation is used for generating the DSRL schema as described
in Section 11.3.
12.7. The <nma:instance-identifier> Annotation
If this annotation element has the @require-instance attribute with
the value of "false", it is ignored. Otherwise it is mapped to the
following Schematron assert:
<sch:assert test="nmf:evaluate(.)">
The element pointed to by "CONTELEM" must exist.
</sch:assert>
The nmf:evaluate() function is an XSLT extension function (see
Extension Functions in [XSLT]) that evaluates an XPath expression at
run time. Such an extension function is available in Extended XSLT
(EXSLT) or provided as a proprietary extension by some XSLT
processors, for example Saxon.
12.8. The @nma:key Annotation
Assume this annotation attribute contains "k_1 k_2 ... k_n", i.e.,
specifies n children of CONTELEM as list keys. The annotation is
then mapped to the following Schematron report:
<sch:report test="CONDITION">
Duplicate key of list "CONTELEM"
</sch:report>
where CONDITION has this form:
preceding-sibling::CONTELEM[C_1 and C_2 and ... and C_n]
Each sub-expression C_i, for i=1,2,...,n, specifies the condition for
violated uniqueness of the key k_i, namely
k_i=current()/k_i
12.9. The @nma:leaf-list Annotation
This annotation is mapped to the following Schematron rule which
detects duplicate entries of a leaf-list:
<sch:report
test=". = preceding-sibling::PREFIX:sorted-entry">
Duplicate leaf-list entry "<sch:value-of select="."/>".
</sch:report>
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See Section 11.2 for a complete example.
12.10. The @nma:leafref Annotation
This annotation is mapped to the following assert:
<sch:assert test="PATH=.">
Leaf "PATH" does not exist for leafref value "VALUE"
</sch:assert>
where PATH is the value of @nma:leafref and VALUE is the value of the
context element in the instance document for which the referred leaf
doesn't exist.
12.11. The @nma:min-elements Annotation
This annotation is mapped to the following Schematron assert:
<sch:assert test="count(../CONTELEM)>=MIN">
List "CONTELEM" - item count must be at least MIN
</sch:assert>
where MIN is the value of @nma:min-elements.
12.12. The @nma:max-elements Annotation
This annotation is mapped to the following Schematron assert:
<sch:assert
test="count(../CONTELEM)<=MAX or preceding-sibling::../CONTELEM">
Number of list items must be at most MAX
</sch:assert>
where MAX is the value of @nma:min-elements.
12.13. The <nma:must> Annotation
This annotation is mapped to the following Schematron assert:
<sch:assert test="EXPRESSION">
MESSAGE
</sch:assert>
where EXPRESSION is the value of the mandatory @assert attribute of
<nma:must>. If the <nma:error-message> subelement exists, MESSAGE is
set to its contents, otherwise it is set to the default message
"Condition EXPRESSION must be true".
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12.14. The <nma:ordered-by> Annotation
This annotation currently has no mapping defined.
12.15. The <nma:status> Annotation
This annotation currently has no mapping defined.
12.16. The @nma:unique Annotation
The mapping of this annotation is almost identical as for @nma:key,
see Section 12.8, with two small differences:
o The value of @nma:unique is a list of descendant schema node
identifiers rather than simple leaf names. However, the XPath
expressions specified in Section 12.8 work without any
modifications if the descendant schema node identifiers are
substituted for k_1, k_2, ..., k_n.
o The message appearing as the text of <sch:report> is different:
"Violated uniqueness for list CONTELEM".
12.17. The @nma:when Annotation
This annotation is mapped to the following Schematron assert:
<sch:assert test="EXPRESSION">
Node "CONTELEM" is only valid when "EXPRESSION" is true.
</sch:assert>
where EXPRESSION is the value of @nma:when.
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13. IANA Considerations
This document requests the following two registrations of namespace
URIs in the IETF XML registry [RFC3688]:
-----------------------------------------------------
URI: urn:ietf:params:xml:ns:netmod:dsdl-annotations:1
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
-----------------------------------------------------
-----------------------------------------------------
URI: urn:ietf:params:xml:ns:netmod:xpath-extensions:1
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
-----------------------------------------------------
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14. Security Considerations
This document defines a procedure that maps data models expressed in
the YANG language to a coordinated set of DSDL schemas. The
procedure itself has no security impact on the Internet.
DSDL schemas obtained by the mapping procedure may be used for
validating the contents of NETCONF messages or entire datastores and
thus provide additional validity checks above those performed by
NETCONF server and client implementations supporting YANG data
models. The strictness of this validation is directly derived from
the source YANG modules that the validated XML data adhere to.
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15. Contributors
The following people contributed significantly to the initial version
of this document:
o Rohan Mahy
o Sharon Chisholm (Ciena)
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16. Acknowledgments
The editor wishes to thank the following individuals who provided
helpful suggestions and/or comments on various versions of this
document: Andy Bierman, Martin Bjorklund, Jirka Kosek, Juergen
Schoenwaelder and Phil Shafer.
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17. References
17.1. Normative References
[DSDL] ISO/IEC, "Document Schema Definition Languages (DSDL) -
Part 1: Overview", ISO/IEC 19757-1, November 2004.
[DSRL] ISO/IEC, "Information Technology - Document Schema
Definition Languages (DSDL) - Part 8: Document Semantics
Renaming Language - DSRL", ISO/IEC 19757-8:2008(E),
December 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[RFC4741] Enns, R., "NETCONF Configuration Protocol", RFC 4741,
December 2006.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
Network Configuration Protocol (NETCONF)", RFC 6020,
September 2010.
[RFC6021] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6021, September 2010.
[RNG] ISO/IEC, "Information Technology - Document Schema
Definition Languages (DSDL) - Part 2: Regular-Grammar-
Based Validation - RELAX NG. Second Edition.", ISO/
IEC 19757-2:2008(E), December 2008.
[RNG-CS] ISO/IEC, "Information Technology - Document Schema
Definition Languages (DSDL) - Part 2: Regular-Grammar-
Based Validation - RELAX NG. AMENDMENT 1: Compact Syntax",
ISO/IEC 19757-2:2003/Amd. 1:2006(E), January 2006.
[RNG-DTD] Clark, J., Ed. and M. Murata, Ed., "RELAX NG DTD
Compatibility", OASIS Committee Specification 3 December
2001, December 2001.
[Schematron]
ISO/IEC, "Information Technology - Document Schema
Definition Languages (DSDL) - Part 3: Rule-Based
Validation - Schematron", ISO/IEC 19757-3:2006(E),
June 2006.
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[XML] Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008,
<http://www.w3.org/TR/2006/REC-xml-20060816>.
[XML-INFOSET]
Tobin, R. and J. Cowan, "XML Information Set (Second
Edition)", World Wide Web Consortium Recommendation REC-
xml-infoset-20040204, February 2004,
<http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.
[XPath] Clark, J. and S. DeRose, "XML Path Language (XPath)
Version 1.0", World Wide Web Consortium
Recommendation REC-xpath-19991116, November 1999,
<http://www.w3.org/TR/1999/REC-xpath-19991116>.
[XSD-D] Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
Second Edition", World Wide Web Consortium
Recommendation REC-xmlschema-2-20041028, October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.
[XSLT] Clark, J., "XSL Transformations (XSLT) Version 1.0", World
Wide Web Consortium Recommendation REC-xslt-19991116,
November 1999.
17.2. Informative References
[DHCPtut] Bjorklund, M., "DHCP Tutorial", November 2007, <http://
www.yang-central.org/twiki/bin/view/Main/DhcpTutorial>.
[RFC1157] Case, J., Fedor, M., Schoffstall, M., and J. Davin,
"Simple Network Management Protocol (SNMP)", STD 15,
RFC 1157, May 1990.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[RFC5013] Kunze, J., "The Dublin Core Metadata Element Set",
RFC 5013, August 2007.
[RFC5277] Chisholm, S. and H. Trevino, "NETCONF Event
Notifications", RFC 5277, July 2008.
[Trang] Clark, J., "Trang: Multiformat schema converter based on
RELAX NG", 2008,
<http://www.thaiopensource.com/relaxng/trang.html>.
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[Vli04] van der Vlist, E., "RELAX NG", O'Reilly , 2004.
[XSD] Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,
"XML Schema Part 1: Structures Second Edition", World Wide
Web Consortium Recommendation REC-xmlschema-1-20041028,
October 2004,
<http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.
[pyang] Bjorklund, M. and L. Lhotka, "pyang: An extensible YANG
validator and converter in Python", 2010,
<http://code.google.com/p/pyang/>.
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Appendix A. RELAX NG Schema for NETMOD-Specific Annotations
This appendix defines the content model for all NETMOD-specific
annotations in the form of RELAX NG named pattern definitions.
<CODE BEGINS> file "nmannot.rng"
<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<define name="config-attribute">
<attribute name="nma:config">
<data type="boolean"/>
</attribute>
</define>
<define name="data-element">
<element name="nma:data">
<ref name="__anyxml__"/>
</element>
</define>
<define name="default-attribute">
<attribute name="nma:default">
<data type="string"/>
</attribute>
</define>
<define name="error-app-tag-element">
<element name="nma:error-app-tag">
<text/>
</element>
</define>
<define name="error-message-element">
<element name="nma:error-message">
<text/>
</element>
</define>
<define name="if-feature-attribute">
<attribute name="nma:if-feature">
<list>
<data type="QName"/>
</list>
</attribute>
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</define>
<define name="implicit-attribute">
<attribute name="nma:implicit">
<data type="boolean"/>
</attribute>
</define>
<define name="instance-identifier-element">
<element name="nma:instance-identifier">
<optional>
<attribute name="nma:require-instance">
<data type="boolean"/>
</attribute>
</optional>
</element>
</define>
<define name="key-attribute">
<attribute name="nma:key">
<list>
<data type="QName"/>
</list>
</attribute>
</define>
<define name="leaf-list-attribute">
<attribute name="nma:leaf-list">
<data type="boolean"/>
</attribute>
</define>
<define name="leafref-attribute">
<attribute name="nma:leafref">
<data type="string"/>
</attribute>
</define>
<define name="mandatory-attribute">
<attribute name="nma:mandatory">
<data type="Name"/>
</attribute>
</define>
<define name="max-elements-attribute">
<attribute name="nma:max-elements">
<data type="nonNegativeInteger"/>
</attribute>
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</define>
<define name="min-elements-attribute">
<attribute name="nma:min-elements">
<data type="nonNegativeInteger"/>
</attribute>
</define>
<define name="module-attribute">
<attribute name="nma:module">
<data type="Name"/>
</attribute>
</define>
<define name="must-element">
<element name="nma:must">
<attribute name="assert">
<data type="string"/>
</attribute>
<interleave>
<optional>
<ref name="error-app-tag-element"/>
</optional>
<optional>
<ref name="error-message-element"/>
</optional>
</interleave>
</element>
</define>
<define name="notifications-element">
<element name="nma:notifications">
<zeroOrMore>
<element name="nma:notification">
<ref name="__anyxml__"/>
</element>
</zeroOrMore>
</element>
</define>
<define name="rpcs-element">
<element name="nma:rpcs">
<zeroOrMore>
<element name="nma:rpc">
<interleave>
<element name="nma:input">
<ref name="__anyxml__"/>
</element>
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<optional>
<element name="nma:output">
<ref name="__anyxml__"/>
</element>
</optional>
</interleave>
</element>
</zeroOrMore>
</element>
</define>
<define name="ordered-by-attribute">
<attribute name="nma:ordered-by">
<choice>
<value>user</value>
<value>system</value>
</choice>
</attribute>
</define>
<define name="status-attribute">
<optional>
<attribute name="nma:status">
<choice>
<value>current</value>
<value>deprecated</value>
<value>obsolete</value>
</choice>
</attribute>
</optional>
</define>
<define name="unique-attribute">
<optional>
<attribute name="nma:unique">
<list>
<data type="token"/>
</list>
</attribute>
</optional>
</define>
<define name="units-attribute">
<optional>
<attribute name="nma:units">
<data type="string"/>
</attribute>
</optional>
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</define>
<define name="when-attribute">
<optional>
<attribute name="nma:when">
<data type="string"/>
</attribute>
</optional>
</define>
<define name="__anyxml__">
<zeroOrMore>
<choice>
<attribute>
<anyName/>
</attribute>
<element>
<anyName/>
<ref name="__anyxml__"/>
</element>
<text/>
</choice>
</zeroOrMore>
</define>
</grammar>
<CODE ENDS>
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Appendix B. Schema-Independent Library
In order to avoid copying the common named pattern definitions to
every RELAX NG schema generated in the second mapping step, the
definitions are collected in a library file - schema-independent
library - which is included by the validating schemas under the file
name "relaxng-lib.rng" (XML syntax) and "relaxng-lib.rnc" (compact
syntax). The included definitions cover patterns for common elements
from base NETCONF [RFC4741] and event notifications [RFC5277].
<CODE BEGINS> file "relaxng-lib.rng"
<?xml version="1.0" encoding="UTF-8"?>
<grammar xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
xmlns:en="urn:ietf:params:xml:ns:netconf:notification:1.0"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<define name="message-id-attribute">
<attribute name="message-id">
<data type="string">
<param name="maxLength">4095</param>
</data>
</attribute>
</define>
<define name="ok-element">
<element name="nc:ok">
<empty/>
</element>
</define>
<define name="eventTime-element">
<element name="en:eventTime">
<data type="dateTime"/>
</element>
</define>
</grammar>
<CODE ENDS>
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Appendix C. Mapping DHCP Data Model - A Complete Example
This appendix demonstrates both steps of the YANG-to-DSDL mapping
applied to the "canonical" DHCP tutorial [DHCPtut] data model. The
input YANG module is shown in Appendix C.1 and the output schemas in
the following two subsections.
The hybrid schema was obtained by the "dsdl" plugin of the pyang tool
[pyang] and the validating DSDL schemas were obtained by XSLT
stylesheets that are also part of pyang distribution.
Due to the limit of 72 characters per line, a few long strings
required manual editing, in particular the regular expression
patterns for IP addresses etc. These were replaced by the
placeholder string "... regex pattern ...". Also, line breaks were
added to several documentation strings and Schematron messages.
Other than that, the results of the automatic translations were not
changed.
C.1. Input YANG Module
module dhcp {
namespace "http://example.com/ns/dhcp";
prefix dhcp;
import ietf-yang-types { prefix yang; }
import ietf-inet-types { prefix inet; }
organization
"yang-central.org";
description
"Partial data model for DHCP, based on the config of
the ISC DHCP reference implementation.";
container dhcp {
description
"configuration and operational parameters for a DHCP server.";
leaf max-lease-time {
type uint32;
units seconds;
default 7200;
}
leaf default-lease-time {
type uint32;
units seconds;
must '. <= ../max-lease-time' {
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error-message
"The default-lease-time must be less than max-lease-time";
}
default 600;
}
uses subnet-list;
container shared-networks {
list shared-network {
key name;
leaf name {
type string;
}
uses subnet-list;
}
}
container status {
config false;
list leases {
key address;
leaf address {
type inet:ip-address;
}
leaf starts {
type yang:date-and-time;
}
leaf ends {
type yang:date-and-time;
}
container hardware {
leaf type {
type enumeration {
enum "ethernet";
enum "token-ring";
enum "fddi";
}
}
leaf address {
type yang:phys-address;
}
}
}
}
}
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grouping subnet-list {
description "A reusable list of subnets";
list subnet {
key net;
leaf net {
type inet:ip-prefix;
}
container range {
presence "enables dynamic address assignment";
leaf dynamic-bootp {
type empty;
description
"Allows BOOTP clients to get addresses in this range";
}
leaf low {
type inet:ip-address;
mandatory true;
}
leaf high {
type inet:ip-address;
mandatory true;
}
}
container dhcp-options {
description "Options in the DHCP protocol";
leaf-list router {
type inet:host;
ordered-by user;
reference "RFC 2132, sec. 3.8";
}
leaf domain-name {
type inet:domain-name;
reference "RFC 2132, sec. 3.17";
}
}
leaf max-lease-time {
type uint32;
units seconds;
default 7200;
}
}
}
}
C.2. Hybrid Schema
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<?xml version="1.0" encoding="UTF-8"?>
<grammar
xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
xmlns:dc="http://purl.org/dc/terms"
xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
xmlns:dhcp="http://example.com/ns/dhcp"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<dc:creator>Pyang 1.0a, DSDL plugin</dc:creator>
<dc:date>2010-06-17</dc:date>
<start>
<grammar nma:module="dhcp" ns="http://example.com/ns/dhcp">
<dc:source>YANG module 'dhcp'</dc:source>
<start>
<nma:data>
<optional>
<element nma:implicit="true" name="dhcp:dhcp">
<interleave>
<a:documentation>
configuration and operational parameters for a DHCP server.
</a:documentation>
<optional>
<element nma:default="7200"
name="dhcp:max-lease-time"
nma:units="seconds">
<data type="unsignedInt"/>
</element>
</optional>
<optional>
<element nma:default="600"
name="dhcp:default-lease-time"
nma:units="seconds">
<data type="unsignedInt"/>
<nma:must assert=". <= ../dhcp:max-lease-time">
<nma:error-message>
The default-lease-time must be less than max-lease-time
</nma:error-message>
</nma:must>
</element>
</optional>
<ref name="_dhcp__subnet-list"/>
<optional>
<element name="dhcp:shared-networks">
<zeroOrMore>
<element nma:key="dhcp:name"
name="dhcp:shared-network">
<element name="dhcp:name">
<data type="string"/>
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</element>
<ref name="_dhcp__subnet-list"/>
</element>
</zeroOrMore>
</element>
</optional>
<optional>
<element name="dhcp:status" nma:config="false">
<zeroOrMore>
<element nma:key="dhcp:address"
name="dhcp:leases">
<element name="dhcp:address">
<ref name="ietf-inet-types__ip-address"/>
</element>
<interleave>
<optional>
<element name="dhcp:starts">
<ref name="ietf-yang-types__date-and-time"/>
</element>
</optional>
<optional>
<element name="dhcp:ends">
<ref name="ietf-yang-types__date-and-time"/>
</element>
</optional>
<optional>
<element name="dhcp:hardware">
<interleave>
<optional>
<element name="dhcp:type">
<choice>
<value>ethernet</value>
<value>token-ring</value>
<value>fddi</value>
</choice>
</element>
</optional>
<optional>
<element name="dhcp:address">
<ref name="ietf-yang-types__phys-address"/>
</element>
</optional>
</interleave>
</element>
</optional>
</interleave>
</element>
</zeroOrMore>
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</element>
</optional>
</interleave>
</element>
</optional>
</nma:data>
<nma:rpcs/>
<nma:notifications/>
</start>
</grammar>
</start>
<define name="ietf-yang-types__phys-address">
<data type="string">
<param name="pattern">([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?</param>
</data>
</define>
<define name="ietf-inet-types__ipv6-address">
<data type="string">
<param name="pattern">... regex pattern ...</param>
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ip-prefix">
<choice>
<ref name="ietf-inet-types__ipv4-prefix"/>
<ref name="ietf-inet-types__ipv6-prefix"/>
</choice>
</define>
<define name="ietf-inet-types__host">
<choice>
<ref name="ietf-inet-types__ip-address"/>
<ref name="ietf-inet-types__domain-name"/>
</choice>
</define>
<define name="ietf-yang-types__date-and-time">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="_dhcp__subnet-list">
<a:documentation>A reusable list of subnets</a:documentation>
<zeroOrMore>
<element nma:key="net" name="subnet">
<element name="net">
<ref name="ietf-inet-types__ip-prefix"/>
</element>
<interleave>
<optional>
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<element name="range">
<interleave>
<optional>
<element name="dynamic-bootp">
<a:documentation>
Allows BOOTP clients to get addresses in this range
</a:documentation>
<empty/>
</element>
</optional>
<element name="low">
<ref name="ietf-inet-types__ip-address"/>
</element>
<element name="high">
<ref name="ietf-inet-types__ip-address"/>
</element>
</interleave>
</element>
</optional>
<optional>
<element name="dhcp-options">
<interleave>
<a:documentation>
Options in the DHCP protocol
</a:documentation>
<zeroOrMore>
<element nma:leaf-list="true" name="router"
nma:ordered-by="user">
<a:documentation>
See: RFC 2132, sec. 3.8
</a:documentation>
<ref name="ietf-inet-types__host"/>
</element>
</zeroOrMore>
<optional>
<element name="domain-name">
<a:documentation>
See: RFC 2132, sec. 3.17
</a:documentation>
<ref name="ietf-inet-types__domain-name"/>
</element>
</optional>
</interleave>
</element>
</optional>
<optional>
<element nma:default="7200" name="max-lease-time"
nma:units="seconds">
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<data type="unsignedInt"/>
</element>
</optional>
</interleave>
</element>
</zeroOrMore>
</define>
<define name="ietf-inet-types__domain-name">
<data type="string">
<param name="pattern">... regex pattern ...</param>
<param name="minLength">1</param>
<param name="maxLength">253</param>
</data>
</define>
<define name="ietf-inet-types__ipv4-prefix">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ipv4-address">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ipv6-prefix">
<data type="string">
<param name="pattern">... regex pattern ...</param>
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ip-address">
<choice>
<ref name="ietf-inet-types__ipv4-address"/>
<ref name="ietf-inet-types__ipv6-address"/>
</choice>
</define>
</grammar>
C.3. Final DSDL Schemas
This appendix contains DSDL schemas that were obtained from the
hybrid schema in Appendix C.2 by XSL transformations. These schemas
can be directly used for validating a reply to unfiltered <nc:get>
with the contents corresponding to the DHCP data model.
The RELAX NG schema (in two parts, as explained in Section 8.2) also
includes the schema-independent library from Appendix B.
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C.3.1. Main RELAX NG Schema for <nc:get> Reply
<?xml version="1.0" encoding="utf-8"?>
<grammar
xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
xmlns:dhcp="http://example.com/ns/dhcp"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
ns="urn:ietf:params:xml:ns:netconf:base:1.0">
<include href="relaxng-lib.rng"/>
<start>
<element name="rpc-reply">
<ref name="message-id-attribute"/>
<element name="data">
<interleave>
<grammar ns="http://example.com/ns/dhcp">
<include href="dhcp-gdefs.rng"/>
<start>
<optional>
<element name="dhcp:dhcp">
<interleave>
<optional>
<element name="dhcp:max-lease-time">
<data type="unsignedInt"/>
</element>
</optional>
<optional>
<element name="dhcp:default-lease-time">
<data type="unsignedInt"/>
</element>
</optional>
<ref name="_dhcp__subnet-list"/>
<optional>
<element name="dhcp:shared-networks">
<zeroOrMore>
<element name="dhcp:shared-network">
<element name="dhcp:name">
<data type="string"/>
</element>
<ref name="_dhcp__subnet-list"/>
</element>
</zeroOrMore>
</element>
</optional>
<optional>
<element name="dhcp:status">
<zeroOrMore>
<element name="dhcp:leases">
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<element name="dhcp:address">
<ref name="ietf-inet-types__ip-address"/>
</element>
<interleave>
<optional>
<element name="dhcp:starts">
<ref name="ietf-yang-types__date-and-time"/>
</element>
</optional>
<optional>
<element name="dhcp:ends">
<ref name="ietf-yang-types__date-and-time"/>
</element>
</optional>
<optional>
<element name="dhcp:hardware">
<interleave>
<optional>
<element name="dhcp:type">
<choice>
<value>ethernet</value>
<value>token-ring</value>
<value>fddi</value>
</choice>
</element>
</optional>
<optional>
<element name="dhcp:address">
<ref name="ietf-yang-types__phys-address"/>
</element>
</optional>
</interleave>
</element>
</optional>
</interleave>
</element>
</zeroOrMore>
</element>
</optional>
</interleave>
</element>
</optional>
</start>
</grammar>
</interleave>
</element>
</element>
</start>
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</grammar>
C.3.2. RELAX NG Schema - Global Named Pattern Definitions
<?xml version="1.0" encoding="utf-8"?>
<grammar
xmlns="http://relaxng.org/ns/structure/1.0"
xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
xmlns:dhcp="http://example.com/ns/dhcp"
datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
<define name="ietf-yang-types__phys-address">
<data type="string">
<param name="pattern">
([0-9a-fA-F]{2}(:[0-9a-fA-F]{2})*)?
</param>
</data>
</define>
<define name="ietf-inet-types__ipv6-address">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ip-prefix">
<choice>
<ref name="ietf-inet-types__ipv4-prefix"/>
<ref name="ietf-inet-types__ipv6-prefix"/>
</choice>
</define>
<define name="ietf-inet-types__host">
<choice>
<ref name="ietf-inet-types__ip-address"/>
<ref name="ietf-inet-types__domain-name"/>
</choice>
</define>
<define name="ietf-yang-types__date-and-time">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="_dhcp__subnet-list">
<zeroOrMore>
<element name="subnet">
<element name="net">
<ref name="ietf-inet-types__ip-prefix"/>
</element>
<interleave>
<optional>
<element name="range">
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<interleave>
<optional>
<element name="dynamic-bootp">
<empty/>
</element>
</optional>
<element name="low">
<ref name="ietf-inet-types__ip-address"/>
</element>
<element name="high">
<ref name="ietf-inet-types__ip-address"/>
</element>
</interleave>
</element>
</optional>
<optional>
<element name="dhcp-options">
<interleave>
<zeroOrMore>
<element name="router">
<ref name="ietf-inet-types__host"/>
</element>
</zeroOrMore>
<optional>
<element name="domain-name">
<ref name="ietf-inet-types__domain-name"/>
</element>
</optional>
</interleave>
</element>
</optional>
<optional>
<element name="max-lease-time">
<data type="unsignedInt"/>
</element>
</optional>
</interleave>
</element>
</zeroOrMore>
</define>
<define name="ietf-inet-types__domain-name">
<data type="string">
<param name="pattern">... regex pattern ...</param>
<param name="minLength">1</param>
<param name="maxLength">253</param>
</data>
</define>
<define name="ietf-inet-types__ipv4-prefix">
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<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ipv4-address">
<data type="string">
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ipv6-prefix">
<data type="string">
<param name="pattern">... regex pattern ...</param>
<param name="pattern">... regex pattern ...</param>
</data>
</define>
<define name="ietf-inet-types__ip-address">
<choice>
<ref name="ietf-inet-types__ipv4-address"/>
<ref name="ietf-inet-types__ipv6-address"/>
</choice>
</define>
</grammar>
C.3.3. Schematron Schema for <nc:get> Reply
<?xml version="1.0" encoding="utf-8"?>
<sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron">
<sch:ns uri="http://example.com/ns/dhcp" prefix="dhcp"/>
<sch:ns uri="urn:ietf:params:xml:ns:netconf:base:1.0" prefix="nc"/>
<sch:pattern abstract="true" id="_dhcp__subnet-list">
<sch:rule context="$start/$pref:subnet">
<sch:report test="preceding-sibling::$pref:subnet
[$pref:net=current()/$pref:net]">
Duplicate key "net"
</sch:report>
</sch:rule>
<sch:rule
context="$start/$pref:subnet/$pref:dhcp-options/$pref:router">
<sch:report test=".=preceding-sibling::router">
Duplicate leaf-list value "<sch:value-of select="."/>"
</sch:report>
</sch:rule>
</sch:pattern>
<sch:pattern id="dhcp">
<sch:rule
context="/nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:default-lease-time">
<sch:assert test=". <= ../dhcp:max-lease-time">
The default-lease-time must be less than max-lease-time
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</sch:assert>
</sch:rule>
<sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
dhcp:shared-networks/dhcp:shared-network">
<sch:report test="preceding-sibling::dhcp:shared-network
[dhcp:name=current()/dhcp:name]">
Duplicate key "dhcp:name"
</sch:report>
</sch:rule>
<sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
dhcp:status/dhcp:leases">
<sch:report test="preceding-sibling::dhcp:leases
[dhcp:address=current()/dhcp:address]">
Duplicate key "dhcp:address"
</sch:report>
</sch:rule>
</sch:pattern>
<sch:pattern id="id2768196" is-a="_dhcp__subnet-list">
<sch:param name="start" value="/nc:rpc-reply/nc:data/dhcp:dhcp"/>
<sch:param name="pref" value="dhcp"/>
</sch:pattern>
<sch:pattern id="id2768215" is-a="_dhcp__subnet-list">
<sch:param name="start"
value="/nc:rpc-reply/nc:data/dhcp:dhcp/
dhcp:shared-networks/dhcp:shared-network"/>
<sch:param name="pref" value="dhcp"/>
</sch:pattern>
</sch:schema>
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C.3.4. DSRL Schema for <nc:get> Reply
<?xml version="1.0" encoding="utf-8"?>
<dsrl:maps
xmlns:dsrl="http://purl.oclc.org/dsdl/dsrl"
xmlns:dhcp="http://example.com/ns/dhcp"
xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data</dsrl:parent>
<dsrl:name>dhcp:dhcp</dsrl:name>
<dsrl:default-content>
<dhcp:max-lease-time>7200</dhcp:max-lease-time>
<dhcp:default-lease-time>600</dhcp:default-lease-time>
</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data/dhcp:dhcp</dsrl:parent>
<dsrl:name>dhcp:max-lease-time</dsrl:name>
<dsrl:default-content>7200</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>/nc:rpc-reply/nc:data/dhcp:dhcp</dsrl:parent>
<dsrl:name>dhcp:default-lease-time</dsrl:name>
<dsrl:default-content>600</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>
/nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:subnet
</dsrl:parent>
<dsrl:name>dhcp:max-lease-time</dsrl:name>
<dsrl:default-content>7200</dsrl:default-content>
</dsrl:element-map>
<dsrl:element-map>
<dsrl:parent>
/nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:shared-networks/
dhcp:shared-network/dhcp:subnet
</dsrl:parent>
<dsrl:name>dhcp:max-lease-time</dsrl:name>
<dsrl:default-content>7200</dsrl:default-content>
</dsrl:element-map>
</dsrl:maps>
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Appendix D. Change Log
RFC Editor: remove this section upon publication as an RFC.
D.1. Changes Between Versions -07 and -08
o Edits based on Gen-ART review.
o Added formal templates in Section 13.
o Created the "Contributors" section and moved the former co-authors
there.
o Indicated the location of both global and local named pattern
definitions in the example hybrid schema in Section 8.1.
o Added reference to EXSLT "evaluate" function.
D.2. Changes Between Versions -06 and -07
o Mapping of 'description', 'reference' and 'units' to the hybrid
schema is now mandatory.
o Improvements and fixes of the text based on the AD review
D.3. Changes Between Versions -05 and -06
o Terminology change: "conceptual tree schema" -> "hybrid schema".
o Changed sectioning markers in the hybrid schema into plain NETMOD-
specific annotations. Hence the former "nmt" namespace is not
used at all.
o Added the following NETMOD-specific annotations: @nma:if-feature,
@nma:leaf-list, @nma:mandatory, @nma:module, removed @nma:
presence.
o Changed the structure of RELAX NG schemas by using embedded
grammars and declaration of namespaces via @ns. This was
necessary for enabling the "chameleon" behavior of global
definitions.
o Schematron validation phases are not used.
o If an XPath expression appears inside a top-level grouping, the
local prefix must be represented using the variable $pref. (This
is related to the previous item.)
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o DHCP example: All RNG schemas are only in the XML syntax. Added
RNG with global definitions.
o Added [XML-INFOSET] to normative references.
o Listed the terms that are defined in other documents.
o The schema for NETMOD-specific annotation is now given only as RNG
named pattern definitions, no more in NVDL.
D.4. Changes Between Versions -04 and -05
o Leafs that take their default value from a typedef and are not
annotated with @nma:default must have @nma:implicit="true".
o Changed code markers CODE BEGINS/ENDS to the form agreed by the
WG.
o Derived types "date-and-time" and "uri" SHOULD be mapped to XSD
"dateTime" and "anyURI" types, respectively.
o Clarified the notion of implicit nodes under under 'case' in
Section 9.1.2.
o Moved draft-ietf-netmod-yang-types-06 to normative references.
o An extra <rng:group> is no more required for the default case of a
choice in the shorthand notation.
D.5. Changes Between Versions -03 and -04
o Implemented ordering rules for list children - keys must go first
and appear in the same order as in the input YANG module.
o The 'case' statement is now mapped to either <rng:group> (inside
RPC operations) or <rng:interleave> (otherwise).
o A nma:default annotation coming from a datatype which the mapping
expands is attached to the <rng:element> pattern where the
expansion occurs. Added an example.
o Documentation statements ('description', 'reference', 'status')
MAY be ignored.
o Single-valued numeric or length range parts are mapped to <rng:
value> pattern or "length" facet.
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o Example for "string" datatype was added.
o Appendix A now uses NVDL for defining NETMOD-specific annotations.
o Added CODE BEGINS/ENDS markers.
o Separated normative and informative references.
o Added URL for XPath extensions namespace.
o Added Section 2 (Terminology and Notation).
o Added Section 14 (Security Considerations).
o Added Section 16 (Acknowledgments).
o Removed compact syntax schema from Appendix B.
o Editorial changes: symbolic citation labels.
D.6. Changes Between Versions -02 and -03
o Changed @nma:default-case to @nma:implicit.
o Changed nma:leafref annotation from element to attribute.
o Added skeleton rule to Section 11.2.
o Reworked Section 11.3, added skeleton element maps,corrected the
example.
o Added section on 'feature' and 'deviation'.
o New Section 9.1 integrating discussion of both optional/mandatory
(was in -02) and implicit nodes (new).
o Reflected that key argument and schema node identifiers are no
more XPath (should be in yang-07).
o Element patterns for implicit containers now must have @nma:
implicit attribute.
o Removed "float32" and "float64" types and added mapping of
"decimal64" with example.
o Removed mapping of 'require-instance' for "leafref" type.
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o Updated RELAX NG schema for NETMOD-specific annotations.
o Updated the DHCP example.
D.7. Changes Between Versions -01 and -02
o Moved Section 7 "NETCONF Content Validation" after Section 6.
o New text about mapping defaults to DSRL, especially in Section 7
and Section 11.3.
o Finished the DHCP example by adding the DSRL schema to Appendix C.
o New @nma:presence annotation was added - it is needed for proper
handling of default contents.
o Section 11.2.1 "Constraints on Mandatory Choice" was added because
these constraints require a combination of RELAX NG and
Schematron.
o Fixed the schema for NETMOD-specific annotations by adding
explicit prefix to all defined elements and attributes.
Previously, the attributes had no namespace.
o Handling of 'feature', 'if-feature' and 'deviation' added.
o Handling of nma:instance-identifier via XSLT extension function.
D.8. Changes Between Versions -00 and -01
o Attributes @nma:min-elements and @nma:max-elements are attached to
<rng:element> (list entry) and not to <rng:zeroOrMore> or <rng:
oneOrMore>.
o Keys and all node identifiers in 'key' and 'unique' statements are
prefixed.
o Fixed the mapping of 'rpc' and 'notification'.
o Removed previous sec. 7.5 "RPC Signatures and Notifications" - the
same information is now contained in Section 10.50 and
Section 10.37.
o Added initial "_" to mangled names of groupings.
o Mandated the use of @xmlns:xxx as the only method for declaring
the target namespace.
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o Added section "Handling of XML Namespaces" to explain the previous
item.
o Completed DHCP example in Appendix C.
o Almost all text about the second mapping step is new.
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Author's Address
Ladislav Lhotka (editor)
CESNET
Email: lhotka@cesnet.cz
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