Internet Draft Vinod Kumar S
NETMOD Working Group Gaurav Agrawal
Category: Informational Anil Kumar S N
Expires: January 9, 2017 July 8, 2016
Defining and Using Metadata for YANG compilers
draft-agv-netmod-yang-compiler-metadata-01
Abstract
This document defines mechanism to defining compiler metadata
(annotations) in YANG modules using YANG extension statement.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Drafts is at http://datatracker.ietf.org/drafts/current/.
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on January 9, 2017.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Keywords . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Terms Defined in Other Documents . . . . . . . . . . . . . 6
2.4. Definitions of New Terms . . . . . . . . . . . . . . . . . 7
3. Defining compiler annotations in YANG . . . . . . . . . . . . 7
3.1. Example Definition . . . . . . . . . . . . . . . . . . . . 8
4. Using Annotations . . . . . . . . . . . . . . . . . . . . . . 10
5. Metadata YANG Module . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
9 Security Considerations . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
11 References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1 Normative References . . . . . . . . . . . . . . . . . . . 14
11.2 Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
YANG started as a data modeling language used to model configuration
data, state data, remote procedure calls, and notifications for
network management protocols. The purpose of YANG was focused on
expressing the data organization while being exchanged over network.
It also addressed the constraints that needs to be taken care by the
data set exchanged.
YANG has out grown the purpose for which it was invented. Due to its
simplicity in structure and flexibility many tools have been
developed which tries to ease the application development by
automating the code generated corresponding to defined schema.
All the implementation related data structures / classes could be
auto generated and applications only concentrate on the business
logic implementation. Applications are being relieved from actual
protocol implementation for exchanging information with external
system.
The purpose of YANG was focused on expressing the data organization
while being exchanged over network. Hence the scope of automation in
application development cannot cater to data organization /
processing within the system.
This gap needs to be addressed in a standardized way so that it's not
compiler / utilities / platform / language specific. This enable
application to be portable across multiple platforms without any
additional effort with respect to data organization.
Also it is required that the mechanism of annotation should not be
in-line with original YANG module/sub-module, so that it will not
result in maintenance issues.
So there is a need to support compiler annotations in YANG, by which
applications can instruct the YANG utilities or compilers to automate
the application development related to data organization /
processing. These annotations should be maintained in additional YANG
module / sub-module which can be optionally consumed by supporting
compilers.
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Typical use cases are:
o Feed input to YANG compiler/utilities which can be used to
automate the code generation based on standard data structure or
collections.
o Enable the code generation to incorporate the design patterns
required by applications.
o Enable the data structure or collections to have multiple indexes
beyond the current supported list's key(s). Since the actual
implementation would required searching the data based on
different leaf combinations.
o Enable applications to model internal data organization, required
for business logic implementation, and not exposed to outside
world.
Usage of compiler annotations are dependent on the compiler consuming
it. This draft is intended to document YANG extension to support
defining compiler annotation framework.It is outside the scope of
this document about the specific compiler annotation(s) definition /
usage. Individual annotation definition and usage SHOULD be
standardized in other docs.
Definition and usage of compiler annotation is limited to a
particular protocol or application development within a device, it
has no effect on how the management information is exchanged between
2 devices over network. A server SHOULD share its YANG file(s) after
removing the compiler annotations that was added for its
implementation. A client MUST ignore any compiler annotations present
in the YANG file(s). A client MAY redefine the compiler annotation as
per its implementation requirements. Clients MAY also add new
annotation depending on its implementation requirements.
This document proposes a systematic way for defining compiler
metadata annotations. For this purpose, YANG extension statement
"compiler-annotation" is defined in the module "agv-yang-compiler-
annotation" (Section 5). Other YANG modules importing this module
can use the "compiler-annotation" statement for defining one or more
compiler annotations.
The benefits of defining the compiler-annotations in a YANG module
are the following:
o Applications can use YANG as a tool to design the application
implementation.
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o Enhance the YANG compiler(s) capability to automate the
application development process.
o Enhance the protocol development to provide better application
development framework.
o YANG could be extended to support data modeling for protocol
beyond NETCONF or RESTCONF.
Due to the rules for YANG extensions (see sec. 6.3.1 in [I-D.ietf-
netmod-rfc6020bis]), compiler-annotation definitions posit relatively
weak conformance requirements. The alternative of introducing a new
built-in YANG mechanism for compiler annotations was considered, but
it was seen as a major change to the language that is inappropriate
for YANG 1.1, which was chartered as a maintenance revision. After
evaluating real-life usage of compiler metadata annotations, it is
designed in such way that the ABNF grammar can seamlessly adapt the
current defined compiler annotations.
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2. Terminology
2.1. Keywords
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].
2.2. Terms Defined in Other Documents
The following terms are defined in [RFC6241]:
o capability,
o client,
o datastore,
o message,
o protocol operation,
o server.
The following terms are defined in [I-D.ietf-netmod-rfc6020bis]:
o action,
o anydata,
o anyxml,
o built-in type,
o container,
o data model,
o data node,
o data tree,
o derived type,
o extension,
o leaf,
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o leaf-list,
o list,
o module,
o RPC input and output.
2.4. Definitions of New Terms
o compiler-annotation: a single item of compiler metadata that is
attached to YANG constructs.
o compiler metadata: additional information that complements a
schema tree.
3. Defining compiler annotations in YANG
Compiler metadata annotations are defined by YANG extension statement
"ca:compiler-annotation". This YANG language extension is defined in
the module "ietf-yang-compiler-annotation" (Section 5).
Sub-statements of "ca:compiler-annotation" are shown in Table 2. They
are all core YANG statements, and the numbers in the second column
refer to the corresponding section in [I-D.ietf-netmod- rfc6020bis]
where each statement is described.
+---------------+---------------------+-------------+
| sub-statement | RFC 6020bis section | cardinality |
+---------------+---------------------+-------------+
| description | 7.21.3 | 0..1 |
| if-feature | 7.20.2 | 0..n |
| reference | 7.21.4 | 0..1 |
| status | 7.21.2 | 0..1 |
| units | 7.3.3 | 0..1 |
| ... | Current Section 5 | 1..n |
+---------------+---------------------+-------------+
Table 2: Substatements of "ca:compiler-annotation".
This draft only specifies a mechanism to define compiler metadata
(annotations) in YANG modules using YANG extension statement. It
provides a generic extension based mechanism, to define the
annotations, specific extensions needs to be defined for specific
data organization annotations as sub statement to compiler annotation
extension.
An compiler annotation can be made conditional by using one or more
"if- feature" statements; the compiler annotation is then consumed by
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compilers and perform the desired operation in compilation.
The semantics and usage rules for a specific compiler-annotation
extensions SHOULD be fully specified in another document.
A compiler-annotation MUST NOT change the schema tree semantics
defined by YANG. For example, it is illegal to define and use an
compiler-annotation that allows modification to data-def-stmts.
The "status" statement can be used exactly as for YANG schema nodes.
3.1. Example Definition
module example-yang {
namespace "urn:ietf:params:xml:ns:yang:example-yang";
prefix "example-yang";
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>";
description
"This YANG module demonstrates the usage of compiler
annotation by any module.";
revision 2016-07-08 {
description
"Initial revision.";
reference
"draft-agv-netmod-yang-compiler-metadata: example YANG which
is annotated";
}
container candidate-servers {
list server {
key "name";
unique "ip port";
leaf name {
type string;
}
leaf ip {
type inet:ip-address;
}
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leaf port {
type inet:port-number;
}
}
}
}
The following module defines the "app-data-structure" compiler-
annotation as specific compiler annotation extension:
module example-compiler-annotation {
namespace "urn:ietf:params:xml:ns:yang:example-compiler-annotation";
prefix "example";
import ietf-yang-compiler-annotation {
prefix "ca";
}
import ietf-yang-app-data-structure-annotation {
prefix "ds";
}
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>";
description
"This YANG module demonstrates the usage of compiler
annotation by any module.";
revision 2016-07-08 {
description
"Initial revision.";
reference
"draft-agv-netmod-yang-compiler-metadata: example of
defining and using compiler annotations with YANG";
}
ca:compiler-annotation /candidate-servers/server {
ds:app-data-structure queue;
}
}
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4. Using Annotations
By defining a YANG module in which a compiler metadata annotation is
defined using the "ca:compiler-annotation" statement, an application
indicates compiler to handle that compiler-annotation according to
the compiler-annotation's definition. That is, the compiler-
annotation uses it as input for automation of code generation or
applications development.
Depending on its semantics, an annotation may have an effect only in
certain schema trees and/or on specific schema node types.
A client MUST NOT use the compiler-annotation to interpret the schema
even if it is advertised by a server.
5. Metadata YANG Module
FC Editor: In this section, replace all occurrences of 'XXXX' with
he actual RFC number and all occurrences of the revision date below
ith the date of RFC publication (and remove this note).
FC Editor: Also please replace all occurrences of 'RFC 6020bis' with
he actual RFC number that will be assigned to [I-D.ietf-netmod-
fc6020bis].
CODE BEGINS> file "ietf-yang-compiler-annotation.yang"
odule ietf-yang-compiler-annotation {
amespace "urn:ietf:params:xml:ns:yang:ietf-yang-compiler-annotation";
refix "ca";
rganization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
ontact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>";
escription
"This YANG module defines an extension statement that allows for
defining compiler annotations.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
'OPTIONAL' in the module text are to be interpreted as described
in RFC 2119 (http://tools.ietf.org/html/rfc2119).";
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revision 2016-07-08 {
description
"Initial revision.";
reference
"draft-agv-netmod-yang-compiler-metadata:
Defining and Using compiler annotations with YANG";
}
extension compiler-annotation {
argument target;
description
"This extension allows for defining compiler annotations for
any body-stmts. The 'ca:compiler-annotation' statement
contains annotations applicable to its target statement
identified by the argument.
It's purpose is to provide additional information to compiler
about implementation of the modeled information.
he argument is a string that identifies a node in the
chema tree. This node is called the compiler annotation's
target node. The target node MUST be a body-stmt as defined
in RFC6020bis.
It MAY be consumed by the compiler of the device supporting
the schema.
The compiler annotations must be defined in a seperate YANG file,
so that there are no maintenance issues.
The ca:compiler-annotation defined with this extension
statement do not affect the namespace or get impacted by
the namespace of the YANG file where it is used.
Semantics of the annotation and other documentation can be
specified using the following standard YANG substatements (all
are optional): 'description', 'reference', 'status', and
'units'.
The presence of a 'if-feature' child to the ca:
compiler-annotation, means the compiler consumes the
annotation when the feature is supported by the device.
Server SHOULD NOT share ca:compiler-annotations YANG files
while sharing schema with a client in protocol exchange.
Client receiving the schema from a Server in protocol
exchange, MUST ignore the YANG files with any
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ca:compiler-annotations extension.
There must be one or more sub statements with specific compiler
annotation extensions. (Note: Specific compiler annotation
extensions SHOULD be covered as a part of other standard
documents.)
} // compiler-annotation
//module agv-yang-compiler-annotation
CODE ENDS>
8. IANA Considerations
RFC Editor: In this section, replace all occurrences of 'XXXX'
with the actual RFC number and all occurrences of the revision date
below with the date of RFC publication (and remove this note).
This document registers a URI in the "IETF XML registry"
[RFC3688]. Following the format in RFC 3688, the following
registration has been made.
------------------------------------------------------------------
URI: urn:agv:params:xml:ns:yang:agv-yang-compiler-annotation
Registrant Contact: The NETMOD WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
------------------------------------------------------------------
This document registers a YANG module in the "YANG Module Names"
registry [RFC6020].
------------------------------------------------------------------
name: agv-yang-compiler-annotation
namespace: urn:agv:params:xml:ns:yang:
agv-yang-compiler-annotation
prefix: md
reference: RFC XXXX
------------------------------------------------------------------
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9 Security Considerations
This document introduces a mechanism for defining compiler metadata
annotations in YANG modules and attaching them to instances of YANG
schema nodes. By itself, this mechanism represents no security
threat. Security implications of a particular compiler-annotation
defined using this mechanism MUST be duly considered and documented
in the the compiler-annotation's definition.
10. Acknowledgments
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11 References
11.1 Normative References
I-D.ietf-netmod-rfc6020bis]
Bjorklund, M., "The YANG 1.1 Data Modeling Language",
draft-ietf-netmod-rfc6020bis-11 (work in progress),
February 2016.
I-D.ietf-netmod-yang-json]
Lhotka, L., "JSON Encoding of Data Modeled with YANG",
draft-ietf-netmod-yang-json-09 (work in progress), March
2016.
RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
11.2 Informative References
[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-10 (work in
progress), March 2016.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<http://www.rfc-editor.org/info/rfc6241>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
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<http://www.rfc-editor.org/info/rfc2119>.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
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Authors' Addresses
Vinod Kumar S
Huawei Technologies India Pvt. Ltd,
Near EPIP Industrial Area,
Kundalahalli Village,
Whitefield,
Bangalore - 560066
EMail: vinods.kumar@huawei.com
Gaurav Agrawal
Huawei Technologies India Pvt. Ltd,
Near EPIP Industrial Area,
Kundalahalli Village,
Whitefield,
Bangalore - 560066
EMail: gaurav.agrawal@huawei.com
Anil Kumar S N
Huawei Technologies India Pvt. Ltd,
Near EPIP Industrial Area,
Kundalahalli Village,
Whitefield,
Bangalore - 560066
EMail: anil.ietf@gmail.com
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