YANG Schema Comparison
draft-ietf-netmod-yang-schema-comparison-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Active".
|
|
|---|---|---|---|
| Authors | Per Andersson , Robert Wilton , Michal Vaško | ||
| Last updated | 2026-05-27 (Latest revision 2026-05-05) | ||
| Replaces | draft-verdt-netmod-yang-schema-comparison | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-netmod-yang-schema-comparison-08
Network Working Group P. Andersson, Ed.
Internet-Draft Ionio Systems
Updates: 7950 (if approved) R. Wilton
Intended status: Standards Track Cisco Systems, Inc.
Expires: 28 November 2026 M. Vaško
CESNET
27 May 2026
YANG Schema Comparison
draft-ietf-netmod-yang-schema-comparison-08
Abstract
This document specifies an algorithm for comparing two revisions of a
YANG schema to determine the scope of changes, and a list of changes,
between the revisions. The output of the algorithm can be used to
help select an appropriate revision-label or YANG semantic version
number for a new revision. Included is also a YANG module describing
possible output of this algorithm.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 28 November 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
Andersson, et al. Expires 28 November 2026 [Page 1]
Internet-Draft YANG Schema Comparison May 2026
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Conventions . . . . . . . . . . . . . . . . . 3
3. Parsed schema tree . . . . . . . . . . . . . . . . . . . . . 4
4. Compiled schema tree . . . . . . . . . . . . . . . . . . . . 4
5. YANG schema tree comparison algorithm . . . . . . . . . . . . 5
5.1. Module identification . . . . . . . . . . . . . . . . . . 6
5.2. Change content . . . . . . . . . . . . . . . . . . . . . 6
5.3. Change conformance . . . . . . . . . . . . . . . . . . . 6
5.3.1. Editorial change . . . . . . . . . . . . . . . . . . 7
5.3.2. Backwards-compatible change . . . . . . . . . . . . . 7
5.3.3. Non-backwards-compatible change . . . . . . . . . . . 7
5.3.4. Extensions . . . . . . . . . . . . . . . . . . . . . 8
5.4. Compiled and parsed schema changes . . . . . . . . . . . 9
6. Comparison tooling . . . . . . . . . . . . . . . . . . . . . 9
7. Schema Comparison YANG Module . . . . . . . . . . . . . . . . 9
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
10.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . 13
10.2. The "YANG Module Names" Registry . . . . . . . . . . . . 14
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1. Normative References . . . . . . . . . . . . . . . . . . 14
11.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Schema Comparison Algorithm Output YANG Module . . . 16
Appendix B. Comparison Examples . . . . . . . . . . . . . . . . 48
B.1. Relaxed Length Module . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
1. Introduction
This document defines the algorithm for comparing two revisions of a
YANG schema. There are two kinds of YANG schemas: on-the-wire or
compiled schema and text or parsed schema.
Andersson, et al. Expires 28 November 2026 [Page 2]
Internet-Draft YANG Schema Comparison May 2026
The compiled schema is what tools use when working with any kinds of
YANG data. Generally, in all the YANG modules, all the schema nodes
need to be fully resolved and have their final form. For example,
every "uses" statement is replaced with the nodes from the
corresponding "grouping", every type referencing a "typedef" is
replaced with the type of the "typedef" and so on. On the other
hand, the parsed schema is comprised of all the YANG modules together
as they are. That means no statements are resolved and they remain
in exactly the same text form as present in the YANG modules.
For determining whether a new revision of a YANG 1.1 module is or is
not backwards-compatible based on all the rules in [RFC7950] and
[I-D.ietf-netmod-yang-module-versioning] , both of these schemas
would be required. Similarly for YANG 1.0, the rules in [RFC6020] .
This document defines an algorithm for comparing either only the
compiled schema or both the parsed and compiled schema.
The output of this algorithm can be utilized by tools processing YANG
instance data to determine what exact changes should they expect and
even how to transform instance data valid for an old revision of a
YANG module to be valid for a newer revision of the same YANG module.
Such tools are typically clients or servers of YANG-driven protocols,
e.g. NETCONF, RESTCONF, or gRPC.
But, the generated data can also be used by YANG module authors to
check all the changes made between 2 revisions. Additionally, it can
assist with deciding what semantic version should the new revision of
the module use based on the [I-D.ietf-netmod-yang-semver] document.
2. Terminology and Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
This document makes use of the following terminology introduced in
the YANG 1.1 Data Modeling Language [RFC7950]:
* module
* schema node
* data node
* data definition statement
Andersson, et al. Expires 28 November 2026 [Page 3]
Internet-Draft YANG Schema Comparison May 2026
3. Parsed schema tree
When a YANG module is parsed and its contents stored in an internal
representation without any statement resolution or modification, the
result is a parsed schema tree. Such a schema tree can be printed
into a YANG module and it should be exactly the same as the loaded
source YANG module.
4. Compiled schema tree
The compiled schema node tree resolves all the statements used for
syntactic abstraction and simplification to obtain one schema node
tree with only data nodes. Textual fields are kept as well because
they may affect backwards compatibility of the whole YANG module.
The steps taken when compiling a parsed schema:
* "Import" statements are resolved by finding the referenced YANG
modules and making their contents available.
* All submodules of a single module are merged to create one large
YANG module.
* "Uses" statements are replaced by the referenced "groupings" and
the YANG nodes they define.
* Types referencing any "typedef" statements are replaced with the
actual type details.
* Augments are resolved by placing the included YANG nodes in their
targets.
* "Deviation" and "refine" statements are applied by changing the
appropriate schema nodes.
* All the "if-feature" statements are evaluated based on the enabled
"features" of implemented YANG modules and the disabled schema
nodes are removed.
After the compilation the result is still a valid YANG module without
the following statements:
* import
* include
* revision
Andersson, et al. Expires 28 November 2026 [Page 4]
Internet-Draft YANG Schema Comparison May 2026
* typedef
* grouping
* augment
* deviation
* feature
* if-feature
* refine
* extension
5. YANG schema tree comparison algorithm
This algorithm is defined for separate YANG modules. When comparing
the compiled schema, all the non data node statements are first
considered and then all the data nodes, recursively. These data
definition statements that are not data nodes are skipped:
* choice
* case
When comparing the parsed schema, the algorithm operates in the same
fashion but compares all the YANG statements. However, only in the
selected YANG module ignoring imported and included modules.
The non data definition statements are considered modified when their
content is changed or any of their substatements are changed. If a
statement is present in the old revision of a module and missing in
the new revision, it is considered removed. Vice-versa, if missing
in the old revision but present in the new revision, it is considered
added.
Data definition statements are compared similarly except that a
change in a descendant data definition statement is not considered a
change of the parent data definition statement but a separate change
instead.
Only statements with any changes are reported and included in the
algorithm output.
Andersson, et al. Expires 28 November 2026 [Page 5]
Internet-Draft YANG Schema Comparison May 2026
5.1. Module identification
When generating the comparison output of two compiled schemas, unique
identification of the modules in question in included. For both the
old and the new revision of the module, its name, revision, list of
submodules, and a leaf-list of enabled features is included. In
addition, the same information is reported for all the imported YANG
modules, recursively. This ensures that if any other output is
produced with a different set of changes for two YANG modules, their
identification information must also differ.
5.2. Change content
Non data definition statements are uniquely identified with their
YANG identifier and data definition statements with their absolute
schema node-ids.
For every change, the changed statement and the parent of the changed
statement are included. While redundant in many cases, it allows to
uniquely report changes in nested statements, e.g. an extension
instance change in the type of a leaf statement. Also, all the
unchanged substatements with their value or content are included for
every changed statement, for both older and newer revision of the
YANG module, if applicable. This ensures that the output includes
all the possibly required information without relying on learning it
from the YANG modules themselves.
5.3. Change conformance
Every change is classified as editorial, backwards-compatible or non-
backwards-compatible. The classification is based on section 11. of
[RFC7950] that mentions most of the possible changes between 2
revisions of a YANG 1.1 module and section 3.1. of
[I-D.ietf-netmod-yang-module-versioning] adds more details about the
exact conformance of statements with various "status" statement
values.
The following text tries to establish general rules of how changes
conformance is selected. Unless there are other statement-specific
rules in the aforementioned documents, these should always apply.
Andersson, et al. Expires 28 November 2026 [Page 6]
Internet-Draft YANG Schema Comparison May 2026
5.3.1. Editorial change
An editorial change MUST NOT affect valid YANG data of the YANG
module in any way. Meaning it MUST NOT make the valid data value
space smaller or larger and it must be exactly the same as in the
module revision without the change. Also, for a change to be
editorial, it MUST NOT affect any YANG module importing the changed
YANG module.
Except for some obvious editorial changes such as fixing a typo in a
"description", changing the local "prefix" of the module is also
categorized as editorial because it does not strictly affect any
importing module. Or, replacing a "uses" statement directly with the
nodes in the referenced "grouping" without any changes.
5.3.2. Backwards-compatible change
For a change to be backwards-compatible, it MUST expand the value
space of valid YANG data. Meaning all the valid YANG data nodes and
values before the change must remain valid but additional nodes or
values can also become valid after the change. Also, backwards-
compatible changes may influence importing modules but MUST NOT cause
them to become invalid. In other words, they may exhibit new
statements whose removal would then be considered a non-backwards-
compatible change but generally must not change the already exposed
statements.
For some examples, the majority of possible backwards-compatible
changes are specifically mentioned directly in [RFC7950].
5.3.3. Non-backwards-compatible change
If a change is not editorial nor backwards-compatible, it MUST be
categorized as non-backwards-compatible. Such changes shrink the
value space of valid YANG data causing some previously valid nodes or
values to no longer be valid. Also, any change that may cause an
importing module to become invalid according to the YANG
specification MUST be non-backwards-compatible.
Andersson, et al. Expires 28 November 2026 [Page 7]
Internet-Draft YANG Schema Comparison May 2026
Examples of a less common or obvious compatibility-breaking changes
are changing the "yang-version" of a YANG module or expanding the
size of a "type". The former change may break importing modules
because of specific rules about "import" statement and the target
module's YANG version. Changing a "type" of a leaf from "uint32" to
"uint64" may seem to fit the definition of a backwards-compatible
change, but it may not be so for some data encodings that use a fixed
binary data chunk (which would grow in size) or even a text format
that may use a different encoding for the two types. Specifically,
the JSON YANG data format [RFC7951] encodes a "uint32" value as a
JSON number but a "uint64" as a JSON string.
5.3.4. Extensions
There are cases when it may be impossible for tooling to accurately
determine the conformance of a change but there is always some
conformance assumed for every statement. The affected ambiguous
statements with their default conformances are:
* pattern - NBC
* when - NBC
* must - NBC
* description - ED
* reference - ED
* presence - ED
* extension instance - BC
Normally, any modification of these statements is reported as the
default assumed change conformance. However, if the author of the
new revision of a YANG module determines that the change of an
aforementioned statement has a different conformance based on the
compatibility rules for the specific statement, they can decide to
use the special extension instances to signify this fact. These are:
* ed-change-at SEMVER
* bc-change-at SEMVER
* nbc-change-at SEMVER
Andersson, et al. Expires 28 November 2026 [Page 8]
Internet-Draft YANG Schema Comparison May 2026
They determine the conformance of the change of the marked statement
to be editorial, backwards-compatible, or non-backwards-compatible,
respectively. The argument is a semantic version of the YANG module
revision that introduced the specific change and these extension
instances are sticky meaning they remain in the module even in its
later revisions.
5.4. Compiled and parsed schema changes
Either only compiled data node changes are reported or both compiled
and parsed statements are compared and their changes generated
depending on the enabled features of the "ietf-yang-schema-
comparison" YANG module.
In the latter case, compiled data node changes are generated
normally. Then, all the other statements are compared in their
original parsed form skipping those that are compiled. Specifically,
all the data node statements are found in the compiled schema tree
meaning they are not compared the second time as part of the parsed
schema tree comparison.
6. Comparison tooling
The "yanglint" tool from the libyang library (in separate Git branch
schema_comparison) is able to generate the "ietf-yang-schema-
comparison" YANG data of two revisions of a YANG module.
7. Schema Comparison YANG Module
YANG module with extensions fine-tuning the classification of
differences between two revisions of YANG schemas.
<CODE BEGINS> file "ietf-yang-schema-comparison@2026-05-27.yang"
module ietf-yang-schema-comparison {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison";
prefix schema-cmp;
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
"WG List: NETCONF WG list <mailto:netmod@ietf.org>
WG Web: https://datatracker.ietf.org/wg/netmod
Author: Michal Vaško
<mailto:mvasko@cesnet.cz>
Author: Rob Wilton
Andersson, et al. Expires 28 November 2026 [Page 9]
Internet-Draft YANG Schema Comparison May 2026
<mailto:rwilton@cisco.com>
Author: Per Andersson
<mailto:per.ietf@ionio.se>";
description
"This YANG 1.1 module contains extensions to support comparison
between different versions of YANG schemas.
Copyright (c) 2026 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (inc above) with actual RFC number and
// remove this note.
revision 2026-05-27 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Schema Comparison";
}
extension ed-change-at {
argument semver;
description
"Marks statements in a new revision of a module
that introduces an editorial change of the statement.
The argument marks the most recent version of the
Andersson, et al. Expires 28 November 2026 [Page 10]
Internet-Draft YANG Schema Comparison May 2026
module where the statement has been changed.
Can only be a substatement of 'pattern', 'when',
'must', 'description', 'reference', 'presence', or
extension instance statements.";
reference
"RFC 7950: The YANG 1.1 Data Modeling Language, section 11;
RFC 6020: YANG - A Data Modeling Language for the Network
Configuration Protocol (NETCONF), section 10";
}
extension bc-change-at {
argument semver;
description
"Marks statements in a new revision of a module
that introduces a backwards-compatible change of
the statement.
The argument marks the most recent version of the
module where the statement has been changed.
Can only be a substatement of 'pattern', 'when',
'must', 'description', 'reference', 'presence', or
extension instance statements.";
reference
"RFC 7950: The YANG 1.1 Data Modeling Language, section 11;
RFC 6020: YANG - A Data Modeling Language for the Network
Configuration Protocol (NETCONF), section 10";
}
extension nbc-change-at {
argument semver;
description
"Marks statements in a new revision of a module
that introduces a non-backwards-compatible change of
the statement.
The argument marks the most recent version of the
module where the statement has been changed.
Can only be a substatement of 'pattern', 'when',
'must', 'description', 'reference', 'presence', or
extension instance statements.";
reference
"RFC 7950: The YANG 1.1 Data Modeling Language, section 11;
RFC 6020: YANG - A Data Modeling Language for the Network
Configuration Protocol (NETCONF), section 10";
}
Andersson, et al. Expires 28 November 2026 [Page 11]
Internet-Draft YANG Schema Comparison May 2026
}
<CODE ENDS>
8. Contributors
This document grew out of the YANG module versioning design team that
started after IETF 101. The following individuals are (or have been)
members of the design team and have worked on the YANG versioning
project:
* Balazs Lengyel
* Benoit Claise
* Bo Wu
* Ebben Aries
* Jason Sterne
* Joe Clarke
* Juergen Schoenwaelder
* Mahesh Jethanandani
* Michael Wang
* Qin Wu
* Reshad Rahman
* Rob Wilton
* Jan Lindblad
* Per Andersson
The ideas for a tooling based comparison of YANG module revisions was
first described in [I-D.clacla-netmod-yang-model-update]. This
document extends upon those initial ideas.
9. Security Considerations
This section follows the template defined in Section 3.7.1 of
[RFC8407].
Andersson, et al. Expires 28 November 2026 [Page 12]
Internet-Draft YANG Schema Comparison May 2026
The YANG module specified in this document defines a schema for data
that is designed to be used by offline tooling to generate output for
differences in supplied YANG modules.
The YANG module specified in this document MAY be accessed via
network management protocols such as NETCONF [RFC6241] or RESTCONF
[RFC8040]. The lowest NETCONF layer is the secure transport layer,
and the mandatory-to-implement secure transport is Secure Shell (SSH)
[RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-
implement secure transport is TLS [RFC8446].
The Network Configuration Access Control Model (NACM) [RFC8341]
provides the means to restrict access for particular NETCONF or
RESTCONF users to a preconfigured subset of all available NETCONF or
RESTCONF protocol operations and content.
When the module is used for offline tooling there are no security
considerations, since the user has full access to all YANG modules
used.
The structure "schema-comparison" contains all the groupings
reflecting the changes between YANG modules. If the data of this
structure are published in online tooling, care needs to be taken so
that knowledge of YANG modules is not leaked.
Since the module does not define any RPCs, actions, or notifications,
the security considerations for such statements are not provided
here.
10. IANA Considerations
10.1. The "IETF XML" Registry
This document register one URI in the "ns" subregistry of the IETF
XML Registry [RFC3688] maintained at
https://www.iana.org/assignments/xml-registry/xml-registry.xhtml#ns.
Following the format in [RFC3688], the following registration is
requested:
URI: urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison
Registrant Contact: The IESG.
XML: N/A, the requested URI is an XML namespace.
Andersson, et al. Expires 28 November 2026 [Page 13]
Internet-Draft YANG Schema Comparison May 2026
10.2. The "YANG Module Names" Registry
This document registers two YANG modules in the YANG Module Names
registry [RFC6020] maintained at https://www.iana.org/assignments/
yang-parameters/yang-paramaters.xhtml. Following the format defined
in [RFC6020], the below registrations are requested:
Name: ietf-yang-schema-comparison
XML Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison
Prefix: schema-cmp
Reference: RFC XXXX
Name: ietf-yang-schema-comparison-output
XML Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison-output
Prefix: schema-cmp-out
Reference: RFC XXXX
11. References
11.1. Normative References
[I-D.ietf-netmod-yang-module-versioning]
Wilton, R., Rahman, R., Lengyel, B., Clarke, J., and J.
Sterne, "Updated YANG Module Revision Handling", Work in
Progress, Internet-Draft, draft-ietf-netmod-yang-module-
versioning-16, 21 April 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-netmod-
yang-module-versioning-16>.
[I-D.ietf-netmod-yang-semver]
Clarke, J., Wilton, R., Rahman, R., Lengyel, B., Sterne,
J., and B. Claise, "YANG Semantic Versioning", Work in
Progress, Internet-Draft, draft-ietf-netmod-yang-semver-
26, 7 May 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-netmod-yang-semver-26>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<https://www.rfc-editor.org/info/rfc3688>.
Andersson, et al. Expires 28 November 2026 [Page 14]
Internet-Draft YANG Schema Comparison May 2026
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<https://www.rfc-editor.org/info/rfc6020>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/info/rfc6241>.
[RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
<https://www.rfc-editor.org/info/rfc6242>.
[RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types",
RFC 6991, DOI 10.17487/RFC6991, July 2013,
<https://www.rfc-editor.org/info/rfc6991>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG",
RFC 7951, DOI 10.17487/RFC7951, August 2016,
<https://www.rfc-editor.org/info/rfc7951>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
Access Control Model", STD 91, RFC 8341,
DOI 10.17487/RFC8341, March 2018,
<https://www.rfc-editor.org/info/rfc8341>.
[RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of
Documents Containing YANG Data Models", RFC 8407,
DOI 10.17487/RFC8407, October 2018,
<https://www.rfc-editor.org/info/rfc8407>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Andersson, et al. Expires 28 November 2026 [Page 15]
Internet-Draft YANG Schema Comparison May 2026
[RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K.,
and R. Wilton, "YANG Library", RFC 8525,
DOI 10.17487/RFC8525, March 2019,
<https://www.rfc-editor.org/info/rfc8525>.
[RFC8791] Bierman, A., Björklund, M., and K. Watsen, "YANG Data
Structure Extensions", RFC 8791, DOI 10.17487/RFC8791,
June 2020, <https://www.rfc-editor.org/info/rfc8791>.
11.2. Informative References
[I-D.clacla-netmod-yang-model-update]
Claise, B., Clarke, J., Lengyel, B., and K. D'Souza, "New
YANG Module Update Procedure", Work in Progress, Internet-
Draft, draft-clacla-netmod-yang-model-update-06, 2 July
2018, <https://datatracker.ietf.org/doc/html/draft-clacla-
netmod-yang-model-update-06>.
Appendix A. Schema Comparison Algorithm Output YANG Module
YANG module with specific output of the schema comparison algorithm
supporting comparison of compiled or parsed and compiled schema tree
of a YANG module. The "ietf-yang-schema-comparison-output" YANG
module imports definitions from the "ietf-yang-types" module defined
in [RFC6991] and "ietf-yang-library" module defined in [RFC8525], and
"ietf-yang-structure-ext" module defined in [RFC8791].
<CODE BEGINS>
file "ietf-yang-schema-comparison-output@2026-05-27.yang"
module ietf-yang-schema-comparison-output {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison-output";
prefix schema-cmp-out;
import ietf-yang-types {
prefix yang;
reference
"RFC 6991: Common YANG Data types";
}
import ietf-yang-library {
prefix yanglib;
reference
"RFC 8525: YANG Library";
}
import ietf-yang-structure-ext {
prefix sx;
reference
"RFC 8791: YANG Data Structure Extensions";
Andersson, et al. Expires 28 November 2026 [Page 16]
Internet-Draft YANG Schema Comparison May 2026
}
organization
"IETF NETMOD (Network Modeling) Working Group";
contact
"WG List: NETCONF WG list <mailto:netmod@ietf.org>
WG Web: https://datatracker.ietf.org/wg/netmod
Author: Michal Vaško
<mailto:mvasko@cesnet.cz>
Author: Rob Wilton
<mailto:rwilton@cisco.com>
Author: Per Andersson
<mailto:per.ietf@ionio.se>";
description
"This YANG 1.1 module contains definitions of output of comparison
between different versions of YANG schemas. The base schema nodes
describe changes in a compiled YANG module with all of its
included submodules and imported modules. The rest of the schema
nodes are optional and describe changes in all the statements of a
single YANG module.
Copyright (c) 2026 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with
or without modification, is permitted pursuant to, and
subject to the license terms contained in, the Revised
BSD License set forth in Section 4.c of the IETF Trust's
Legal Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC
itself for full legal notices.
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL',
'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED',
'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document
are to be interpreted as described in BCP 14 (RFC 2119)
(RFC 8174) when, and only when, they appear in all
capitals, as shown here.";
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
// RFC Ed.: replace XXXX (inc above) with actual RFC number and
Andersson, et al. Expires 28 November 2026 [Page 17]
Internet-Draft YANG Schema Comparison May 2026
// remove this note.
revision 2026-05-27 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Schema Comparison";
}
feature parsed-schema {
description
"Compare also the statements removed from the compiled schema to
get all the backwards-compatible and non-backwards-compatible
changes possible for a YANG module.";
reference
"RFC 7950: The YANG 1.1 Data Modeling Language, section 11;
RFC 6020: YANG - A Data Modeling Language for the Network
Configuration Protocol (NETCONF), section 10";
}
typedef schema-node-path {
type string;
description
"Node schema path (node-id). A generic type is used to not enforce
their evaluation or validation in this context.";
}
typedef schema-stmt-path {
type string;
description
"Path to a statement. Any non data node parents are encoded
specially.";
}
typedef stmt-type {
type enumeration {
enum base {
description
"YANG statement 'base'.";
}
enum bit {
description
"YANG statement 'bit'.";
}
enum config {
description
"YANG statement 'config'.";
}
Andersson, et al. Expires 28 November 2026 [Page 18]
Internet-Draft YANG Schema Comparison May 2026
enum contact {
description
"YANG statement 'contact'.";
}
enum default {
description
"YANG statement 'default'.";
}
enum description {
description
"YANG statement 'description'.";
}
enum deviate {
description
"YANG statement 'deviate'.";
}
enum deviation {
description
"YANG statement 'deviation'.";
}
enum enum {
description
"YANG statement 'enum'.";
}
enum error-app-tag {
description
"YANG statement 'error-app-tag'.";
}
enum error-message {
description
"YANG statement 'error-message'.";
}
enum extension {
description
"YANG statement 'extension'.";
}
enum extension-instance {
description
"Any extension instance YANG statement.";
}
enum feature {
description
"YANG statement 'feature'.";
}
enum fraction-digits {
description
"YANG statement 'fraction-digits'.";
}
Andersson, et al. Expires 28 November 2026 [Page 19]
Internet-Draft YANG Schema Comparison May 2026
enum identity {
description
"YANG statement 'identity'.";
}
enum if-feature {
description
"YANG statement 'if-feature'.";
}
enum import {
description
"YANG statement 'import'.";
}
enum include {
description
"YANG statement 'include'.";
}
enum length {
description
"YANG statement 'length'.";
}
enum mandatory {
description
"YANG statement 'mandatory'.";
}
enum max-elements {
description
"YANG statement 'max-elements'.";
}
enum min-elements {
description
"YANG statement 'min-elements'.";
}
enum must {
description
"YANG statement 'must'.";
}
enum node {
description
"YANG statement 'container', 'leaf', 'leaf-list', 'list',
'anydata', 'anyxml', 'rpc', 'action', or 'notification'. If
the parsed schema is also compared, it can additionally be
'choice', 'case', 'input', 'output', 'uses', 'augment', or
'grouping'.";
}
enum ordered-by {
description
"YANG statement 'ordered-by'.";
}
Andersson, et al. Expires 28 November 2026 [Page 20]
Internet-Draft YANG Schema Comparison May 2026
enum organization {
description
"YANG statement 'organization'.";
}
enum path {
description
"YANG statement 'path'.";
}
enum pattern {
description
"YANG statement 'pattern'.";
}
enum prefix {
description
"YANG statement 'prefix'.";
}
enum presence {
description
"YANG statement 'presence'.";
}
enum range {
description
"YANG statement 'range'.";
}
enum reference {
description
"YANG statement 'reference'.";
}
enum refine {
description
"YANG statement 'refine'.";
}
enum require-instance {
description
"YANG statement 'require-instance'.";
}
enum revision-date {
description
"YANG statement 'revision-date'.";
}
enum status {
description
"YANG statement 'status'.";
}
enum type {
description
"YANG statement 'type'.";
}
Andersson, et al. Expires 28 November 2026 [Page 21]
Internet-Draft YANG Schema Comparison May 2026
enum typedef {
description
"YANG statement 'typedef'.";
}
enum units {
description
"YANG statement 'units'.";
}
enum unique {
description
"YANG statement 'unique'.";
}
enum when {
description
"YANG statement 'when'.";
}
enum yang-version {
description
"YANG statement 'yang-version'.";
}
}
description
"Type of the statement that a change affects.";
}
typedef revision-or-empty {
type union {
type empty;
type yanglib:revision-identifier;
}
description
"Module or submodule revision. If it has none, an empty value is
used.";
}
grouping if-feature-stmts {
description
"Describes changes of all the if-features on a statement.";
leaf-list if-feature {
type string;
description
"Value of an if-feature statement.";
}
}
grouping ext-instance-stmt {
description
"Describes changes of an extension instance.";
Andersson, et al. Expires 28 November 2026 [Page 22]
Internet-Draft YANG Schema Comparison May 2026
leaf module {
type yang:yang-identifier;
mandatory true;
description
"Module with the extension definition of an extension
instance.";
}
leaf name {
type yang:yang-identifier;
mandatory true;
description
"Name of the extension defition of an extension instance.";
}
leaf argument {
type string;
description
"Argument used of an extension definition.";
}
anydata substatements {
description
"Any substatements of the extension instance.";
}
}
grouping ext-instance-stmts {
description
"Describes changes of all the extension instances.";
list ext-instance {
description
"List of extension-instance substatements.";
uses ext-instance-stmt;
}
}
grouping status-stmt {
description
"Describes a status statement change.";
leaf status {
type enumeration {
enum current {
description
"Current effective status of a statement.";
}
enum deprecated {
description
"Deprecated effective status of a statement.";
}
enum obsolete {
Andersson, et al. Expires 28 November 2026 [Page 23]
Internet-Draft YANG Schema Comparison May 2026
description
"Obsolete effective status of a statement.";
}
}
mandatory true;
description
"Status substatement value.";
}
}
grouping must-stmts {
description
"Describes changes of all the must statements of a specific parent
statement.";
list must {
description
"List of must substatements.";
leaf condition {
type string;
description
"Condition substatement value.";
}
uses restriction-substmts;
}
}
grouping when-stmts {
description
"Describes changes of all the when statements of a specific parent
statement.";
list when {
description
"List of when substatements.";
leaf condition {
type string;
description
"Condition substatement value.";
}
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
Andersson, et al. Expires 28 November 2026 [Page 24]
Internet-Draft YANG Schema Comparison May 2026
uses status-stmt;
uses ext-instance-stmts;
}
}
grouping restriction-substmts {
description
"Common substatements shared by all restriction statements.";
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
leaf error-message {
type string;
description
"Error-message substatement value.";
}
leaf error-app-tag {
type string;
description
"Error-app-tag substatement value.";
}
uses ext-instance-stmts;
}
grouping type-substmts {
description
"Describes a type statement change.";
leaf base-type {
type enumeration {
enum int8 {
description
"YANG built-in type 'int8'.";
}
enum int16 {
description
"YANG built-in type 'int16'.";
}
enum int32 {
description
"YANG built-in type 'int32'.";
}
Andersson, et al. Expires 28 November 2026 [Page 25]
Internet-Draft YANG Schema Comparison May 2026
enum int64 {
description
"YANG built-in type 'int64'.";
}
enum uint8 {
description
"YANG built-in type 'uint8'.";
}
enum uint16 {
description
"YANG built-in type 'uint16'.";
}
enum uint32 {
description
"YANG built-in type 'uint32'.";
}
enum uint64 {
description
"YANG built-in type 'uint64'.";
}
enum decimal64 {
description
"YANG built-in type 'decimal64'.";
}
enum string {
description
"YANG built-in type 'string'.";
}
enum boolean {
description
"YANG built-in type 'boolean'.";
}
enum enumeration {
description
"YANG built-in type 'enumeration'.";
}
enum bits {
description
"YANG built-in type 'bits'.";
}
enum binary {
description
"YANG built-in type 'binary'.";
}
enum leafref {
description
"YANG built-in type 'leafref'.";
}
Andersson, et al. Expires 28 November 2026 [Page 26]
Internet-Draft YANG Schema Comparison May 2026
enum identityref {
description
"YANG built-in type 'identityref'.";
}
enum empty {
description
"YANG built-in type 'empty'.";
}
enum union {
description
"YANG built-in type 'union'.";
}
enum instance-identifier {
description
"YANG built-in type 'instance-identifier'.";
}
}
description
"Type substatement value.";
}
container range {
description
"Range statement substatements.";
list interval {
description
"Intervals of a range statement.";
leaf min {
type int64;
description
"Lower boundary of an interval of a range statement.";
}
leaf max {
type int64;
description
"Upper boundary of an interval of a range statement.";
}
}
uses restriction-substmts;
}
container length {
description
"Length statement substatements.";
list interval {
description
"Intervals of a length statement.";
leaf min {
type uint64;
description
Andersson, et al. Expires 28 November 2026 [Page 27]
Internet-Draft YANG Schema Comparison May 2026
"Lower boundary of an interval of a length statement.";
}
leaf max {
type uint64;
description
"Upper boundary of an interval of a length statement.";
}
}
uses restriction-substmts;
}
leaf fraction-digits {
type uint8;
description
"Fraction-digits substatement value.";
}
list pattern {
description
"List of pattern statements.";
leaf expression {
type string;
description
"Pattern substatement value.";
}
leaf inverted {
type boolean;
description
"A value of true indicates that the pattern's 'modifier'
substatement is 'invert-match'.";
reference
"RFC 7950 Section 9.4.6";
}
uses restriction-substmts;
}
list enum {
key "name";
ordered-by user;
description
"List of enum statements. Keeps the same order of the statements
as in the module.";
leaf name {
type yang:yang-identifier;
description
"Enum statement name.";
}
uses if-feature-stmts {
if-feature "parsed-schema";
}
leaf description {
Andersson, et al. Expires 28 November 2026 [Page 28]
Internet-Draft YANG Schema Comparison May 2026
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
leaf value {
type int32;
description
"Value substatement value.";
}
uses status-stmt;
uses ext-instance-stmts;
}
list bit {
key "name";
ordered-by user;
description
"List of bit statements. Keeps the same order of the statements
as in the module.";
leaf name {
type yang:yang-identifier;
description
"Bit statement name.";
}
uses if-feature-stmts {
if-feature "parsed-schema";
}
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
leaf position {
type uint32;
description
"Position substatement value.";
}
uses status-stmt;
uses ext-instance-stmts;
Andersson, et al. Expires 28 November 2026 [Page 29]
Internet-Draft YANG Schema Comparison May 2026
}
leaf path {
type string;
description
"Path substatement value.";
}
leaf require-instance {
type boolean;
description
"Require-instance substatement value.";
}
leaf-list base {
type yang:yang-identifier;
description
"List of base substatement values.";
}
uses ext-instance-stmts;
}
grouping type-parsed-substmts {
description
"Describes a parsed type statement change.";
leaf name {
type yang:yang-identifier;
description
"Type argument substatement value.";
}
container range {
description
"Range statement substatements.";
leaf restriction {
type string;
description
"Range argument substatement value.";
}
uses restriction-substmts;
}
container length {
description
"Length statement substatements.";
leaf restriction {
type string;
description
"Length argument substatement value.";
}
uses restriction-substmts;
}
leaf fraction-digits {
Andersson, et al. Expires 28 November 2026 [Page 30]
Internet-Draft YANG Schema Comparison May 2026
type uint8;
description
"Fraction-digits substatement value.";
}
list pattern {
description
"List of pattern statements.";
leaf expression {
type string;
description
"Pattern substatement value.";
}
leaf inverted {
type empty;
description
"Inverted substatement value.";
}
uses restriction-substmts;
}
list enum {
key "name";
ordered-by user;
description
"List of enum statements. Keeps the same order of the statements
as in the module.";
leaf name {
type yang:yang-identifier;
description
"Enum statement name.";
}
uses if-feature-stmts;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
leaf value {
type int32;
description
"Value substatement value.";
}
uses status-stmt;
uses ext-instance-stmts;
Andersson, et al. Expires 28 November 2026 [Page 31]
Internet-Draft YANG Schema Comparison May 2026
}
list bit {
key "name";
ordered-by user;
description
"List of bit statements. Keeps the same order of the statements
as in the module.";
leaf name {
type yang:yang-identifier;
description
"Bit statement name.";
}
uses if-feature-stmts;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
leaf position {
type uint32;
description
"Position substatement value.";
}
uses status-stmt;
uses ext-instance-stmts;
}
leaf path {
type string;
description
"Path substatement value.";
}
leaf require-instance {
type boolean;
description
"Require-instance substatement value.";
}
leaf-list base {
type yang:yang-identifier;
description
"List of base substatement values.";
}
uses ext-instance-stmts;
}
Andersson, et al. Expires 28 November 2026 [Page 32]
Internet-Draft YANG Schema Comparison May 2026
grouping refine-deviate-node-substmts {
description
"All substatements of a data-definition node that can be changed
by both a refine and deviate statement.";
uses must-stmts;
leaf-list default {
type string;
description
"List of default substatement values.";
}
leaf config {
type boolean;
description
"Config substatement value.";
}
leaf mandatory {
type boolean;
description
"Mandatory substatement value.";
}
leaf min-elements {
type uint32;
description
"Min-elements substatement value.";
}
leaf max-elements {
type uint32;
description
"Max-elements substatement value.";
}
}
grouping node-substmts {
description
"All substatements of a data-definition node.";
uses if-feature-stmts {
if-feature "parsed-schema";
}
uses when-stmts;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
Andersson, et al. Expires 28 November 2026 [Page 33]
Internet-Draft YANG Schema Comparison May 2026
}
uses status-stmt;
uses refine-deviate-node-substmts;
leaf-list key {
type yang:yang-identifier;
description
"Leaf-list of nodes referenced by a key statement.";
}
leaf ordered-by {
type enumeration {
enum system {
description
"System-ordered list or leaf-list of items.";
}
enum user {
description
"User-ordered list or leaf-list of items.";
}
}
description
"Ordered-by substatement value.";
}
container type {
description
"Type substatement.";
uses type-substmts;
list union-type {
description
"List of a union type substatements.";
uses type-substmts;
}
}
leaf units {
type string;
description
"Units substatement value.";
}
list unique {
description
"List of unique substatements.";
leaf-list node {
type yang:yang-identifier;
description
"List of nodes referenced by a unique substatement.";
}
}
leaf presence {
type boolean;
Andersson, et al. Expires 28 November 2026 [Page 34]
Internet-Draft YANG Schema Comparison May 2026
description
"Indicates whether a presence substatement is defined for
the container in the compiled schema. The textual argument
of 'presence' is reported via the parsed schema comparison
(see the 'presence' leaf in 'parsed-substmts').";
}
uses ext-instance-stmts;
}
grouping module-substmts {
description
"All non-data-definition substatements of a module.";
leaf yang-version {
type string;
description
"YANG version substatement value.";
}
leaf prefix {
if-feature "parsed-schema";
type string;
description
"Prefix substatement value.";
}
container import {
if-feature "parsed-schema";
presence "Exists only when there is a difference in this import.";
description
"Import substatements.";
leaf module {
type yang:yang-identifier;
mandatory true;
description
"Imported module.";
}
leaf prefix {
type yang:yang-identifier;
mandatory true;
description
"Imported module prefix.";
}
leaf revision-date {
type yanglib:revision-identifier;
description
"Imported module revision-date.";
}
leaf description {
type string;
description
Andersson, et al. Expires 28 November 2026 [Page 35]
Internet-Draft YANG Schema Comparison May 2026
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses ext-instance-stmts;
}
container include {
if-feature "parsed-schema";
presence
"Exists only when there is a difference in this include.";
description
"Include substatements.";
leaf submodule {
type yang:yang-identifier;
mandatory true;
description
"Included submodule.";
}
leaf revision-date {
type yanglib:revision-identifier;
description
"Included submodule revision-date.";
}
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses ext-instance-stmts;
}
leaf organization {
type string;
description
"Organization substatement value.";
}
leaf contact {
type string;
description
"Contact substatement value.";
}
Andersson, et al. Expires 28 November 2026 [Page 36]
Internet-Draft YANG Schema Comparison May 2026
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
container extension {
if-feature "parsed-schema";
presence
"Exists only when there is a difference in this extension.";
description
"Extension substatements.";
leaf name {
type yang:yang-identifier;
mandatory true;
description
"Extension name.";
}
leaf argument {
type yang:yang-identifier;
description
"Argument substatement value.";
}
uses status-stmt;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses ext-instance-stmts;
}
container feature {
if-feature "parsed-schema";
presence
"Exists only when there is a difference in this feature.";
description
"Feature substatements.";
leaf name {
type yang:yang-identifier;
Andersson, et al. Expires 28 November 2026 [Page 37]
Internet-Draft YANG Schema Comparison May 2026
mandatory true;
description
"Feature name.";
}
uses if-feature-stmts;
uses status-stmt;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses ext-instance-stmts;
}
container identity {
description
"Identity substatements.";
leaf name {
type yang:yang-identifier;
mandatory true;
description
"Identity statement name.";
}
uses if-feature-stmts {
if-feature "parsed-schema";
}
leaf-list base {
if-feature "parsed-schema";
type yang:yang-identifier;
description
"List of bases of an identity.";
}
uses ext-instance-stmts;
}
container deviation {
if-feature "parsed-schema";
presence
"Exists only when there is a difference in this deviation.";
description
"Deviation substatements.";
leaf target {
type string;
mandatory true;
description
Andersson, et al. Expires 28 November 2026 [Page 38]
Internet-Draft YANG Schema Comparison May 2026
"Deviation target argument.";
}
list deviate {
min-elements 1;
description
"List of deviate substatements.";
leaf argument {
type enumeration {
enum not-supported {
description
"Deviate 'not-supported' argument value.";
}
enum add {
description
"Deviate 'add' argument value.";
}
enum replace {
description
"Deviate 'replace' argument value.";
}
enum delete {
description
"Deviate 'delete' argument value.";
}
}
mandatory true;
description
"Deviate argument value.";
}
uses refine-deviate-node-substmts;
container type {
description
"Type substatement.";
uses type-parsed-substmts;
list union-type {
description
"List of a union type substatements.";
uses type-parsed-substmts;
}
}
leaf units {
type string;
description
"Units substatement value.";
}
list unique {
description
"List of unique substatements.";
Andersson, et al. Expires 28 November 2026 [Page 39]
Internet-Draft YANG Schema Comparison May 2026
leaf-list node {
type yang:yang-identifier;
description
"List of nodes referenced by a unique substatement.";
}
}
}
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses ext-instance-stmts;
}
container ext-instance {
presence
"Exists only when there is a difference in this
extension-instance.";
description
"Extension-instance substatements.";
uses ext-instance-stmt;
}
}
grouping parsed-substmts {
description
"All parsed-only statements that can be direct substatements of a
module or nested in a node.";
uses if-feature-stmts {
if-feature "parsed-schema";
}
uses when-stmts;
leaf description {
type string;
description
"Description substatement value.";
}
leaf reference {
type string;
description
"Reference substatement value.";
}
uses status-stmt;
Andersson, et al. Expires 28 November 2026 [Page 40]
Internet-Draft YANG Schema Comparison May 2026
uses refine-deviate-node-substmts;
container type {
description
"Type substatement.";
uses type-parsed-substmts;
list union-type {
description
"List of a union type substatements.";
uses type-parsed-substmts;
}
}
leaf units {
type string;
description
"Units substatement value.";
}
leaf presence {
type string;
description
"Presence substatement value.";
}
uses ext-instance-stmts;
}
grouping conformance-type {
description
"Conformance type of a change.";
leaf conformance {
type enumeration {
enum editorial {
description
"Editorial change.";
}
enum backwards-compatible {
description
"Backwards-compatible change.";
}
enum non-backwards-compatible {
description
"Non-backwards-compatible change.";
}
}
mandatory true;
description
"Conformance information of a change in the compared YANG
modules.";
}
}
Andersson, et al. Expires 28 November 2026 [Page 41]
Internet-Draft YANG Schema Comparison May 2026
grouping change-info {
description
"Details of a single change.";
list changed {
key "stmt";
min-elements 1;
description
"List of changes.";
leaf stmt {
type stmt-type;
description
"Changed statement.";
}
leaf parent-stmt {
type stmt-type;
description
"Parent statement of the changed statement.";
}
leaf change {
type enumeration {
enum modified {
description
"Statement existed and was modified.";
}
enum added {
description
"Statement was added.";
}
enum removed {
description
"Statement was removed.";
}
enum moved {
description
"Statement was moved and the position affects the
meaning.";
}
}
mandatory true;
description
"Type of change of the statement.";
}
uses conformance-type;
}
}
grouping module-params {
description
Andersson, et al. Expires 28 November 2026 [Page 42]
Internet-Draft YANG Schema Comparison May 2026
"Identification details of a processed YANG module.";
leaf module {
type yang:yang-identifier;
mandatory true;
description
"Compared module name.";
}
leaf revision {
type revision-or-empty;
mandatory true;
description
"Compared module revision.";
}
list submodule {
key "name revision";
leaf name {
type yang:yang-identifier;
mandatory true;
description
"Submodule name.";
}
leaf revision {
type revision-or-empty;
mandatory true;
description
"Submodule revision.";
}
description
"Submodule of the main module.";
}
leaf-list enabled-feature {
type yang:yang-identifier;
description
"All the enabled features of the module.";
}
}
grouping parsed-info {
description
"Information about all the changed parsed-only statements.";
list parsed-comparison {
description
"Information about parsed-only statement changes.";
leaf parent-path {
type schema-stmt-path;
description
"Path to the parent statement. Not set if a direct
substatement of module or submodule.";
Andersson, et al. Expires 28 November 2026 [Page 43]
Internet-Draft YANG Schema Comparison May 2026
}
leaf identifier {
type string;
mandatory true;
description
"Identifier of the statement, may include a prefix.";
}
leaf stmt-type {
type enumeration {
enum choice {
description
"YANG statement 'choice' node.";
}
enum case {
description
"YANG statement 'case' node.";
}
enum input {
description
"YANG statement 'input' node.";
}
enum output {
description
"YANG statement 'output' node.";
}
enum uses {
description
"YANG statement 'uses' node.";
}
enum grouping {
description
"YANG statement 'grouping' node.";
}
enum augment {
description
"YANG statement 'augment' node.";
}
enum refine {
description
"YANG statement 'refine' node.";
}
enum typedef {
description
"YANG statement 'typedef'.";
}
}
mandatory true;
description
Andersson, et al. Expires 28 November 2026 [Page 44]
Internet-Draft YANG Schema Comparison May 2026
"Type of the changed data-definition statement.";
}
uses change-info;
container old {
description
"Changed parsed statements in the older revision of the YANG
module.";
uses parsed-substmts;
}
container new {
description
"Changed parsed statements in the newer revision of the YANG
module.";
uses parsed-substmts;
}
}
}
grouping node-info {
description
"Information about all the changed compiled nodes.";
list node-comparison {
key "node";
ordered-by user;
description
"Information about data-definition (node) statement substatement
changes. Keeps the traversed order of the nodes by the
algorithm. It SHOULD follow the depth-first search order.";
leaf node {
type schema-node-path;
description
"Path to the changed data-definition statement.";
}
leaf node-type {
type enumeration {
enum container {
description
"YANG statement 'container' node.";
}
enum leaf {
description
"YANG statement 'leaf' node.";
}
enum leaf-list {
description
"YANG statement 'leaf-list' node.";
}
enum list {
Andersson, et al. Expires 28 November 2026 [Page 45]
Internet-Draft YANG Schema Comparison May 2026
description
"YANG statement 'list' node.";
}
enum anydata {
description
"YANG statement 'anydata' node.";
}
enum anyxml {
description
"YANG statement 'anyxml' node.";
}
enum rpc {
description
"YANG statement 'rpc' node.";
}
enum action {
description
"YANG statement 'action' node.";
}
enum notification {
description
"YANG statement 'notification' node.";
}
}
mandatory true;
description
"Type of the changed data-definition statement.";
}
uses change-info;
container old {
description
"All the node substatements in the older revision of the YANG
module.";
uses node-substmts;
}
container new {
description
"All the node substatements in the newer revision of the YANG
module.";
uses node-substmts;
}
}
}
sx:structure schema-comparison {
description
"Schema comparison details.";
list schema {
Andersson, et al. Expires 28 November 2026 [Page 46]
Internet-Draft YANG Schema Comparison May 2026
description
"Instance of a schema comparison of 2 YANG modules in different
revisions with all their imports.";
container source {
description
"Source module information.";
uses module-params;
}
list source-import {
key "module revision";
description
"List of source module imported modules information.";
uses module-params;
}
container target {
description
"Target module information.";
uses module-params;
}
list target-import {
key "module revision";
description
"List of target module imported modules information.";
uses module-params;
}
uses conformance-type;
list module-comparison {
description
"Information about direct module statement substatement
changes.";
uses change-info;
container old {
description
"Changed statements in the older revision of the YANG
module.";
uses module-substmts;
}
container new {
description
"Changed statements in the newer revision of the YANG
module.";
uses module-substmts;
}
}
uses parsed-info {
if-feature "parsed-schema";
}
uses node-info;
Andersson, et al. Expires 28 November 2026 [Page 47]
Internet-Draft YANG Schema Comparison May 2026
}
}
}
<CODE ENDS>
Appendix B. Comparison Examples
This section provides various examples of the output of the
comparison algorithm defined in this document to illustrate it on
actual YANG modules.
B.1. Relaxed Length Module
An example module comparison with a typedef length restriction
relaxed and a new leaf added.
The generated diff includes both parsed and compiled changes. In the
parsed comparison the specific range change is reported as backwards-
compatible since the restriction was loosened. In the compiled node
comparison the exact same change is reported because the leaf is
using the same typedef, whose change also affects the leaf. The new
added leaf is also reported and marked as backwards-compatible.
<CODE BEGINS> file "mod@2025-01-01.yang"
module mod {
namespace "urn:mod";
prefix m;
yang-version 1.1;
revision 2025-01-01;
typedef my-string {
type string {
length "1..10";
}
}
container cont {
leaf l {
type my-string;
}
}
}
<CODE ENDS>
Andersson, et al. Expires 28 November 2026 [Page 48]
Internet-Draft YANG Schema Comparison May 2026
<CODE BEGINS> file "mod@2025-06-01.yang"
module mod {
namespace "urn:mod";
prefix m;
yang-version 1.1;
revision 2025-06-01;
revision 2025-01-01;
typedef my-string {
type string {
length "1..20";
}
}
container cont {
leaf l {
type my-string;
}
leaf l2 {
type int32;
}
}
}
<CODE ENDS>
<CODE BEGINS> file "mod_comparison.json"
{
"ietf-yang-schema-comparison:schema-comparison": {
"schema": [
{
"source": {
"module": "mod",
"revision": "2025-01-01"
},
"target": {
"module": "mod",
"revision": "2025-06-01"
},
"conformance": "backwards-compatible",
"parsed-comparison": [
{
"parent-path": "/",
"identifier": "my-string",
"stmt-type": "typedef",
"changed": [
{
Andersson, et al. Expires 28 November 2026 [Page 49]
Internet-Draft YANG Schema Comparison May 2026
"stmt": "length",
"parent-stmt": "typedef",
"change": "modified",
"conformance": "backwards-compatible"
}
],
"old": {
"type": {
"name": "string",
"length": {
"restriction": "1..10"
}
}
},
"new": {
"type": {
"name": "string",
"length": {
"restriction": "1..20"
}
}
}
}
],
"node-comparison": [
{
"node": "/mod:cont/l",
"node-type": "leaf",
"changed": [
{
"stmt": "length",
"change": "modified",
"conformance": "backwards-compatible"
}
],
"old": {
"status": "current",
"config": true,
"mandatory": false,
"type": {
"base-type": "string",
"length": {
"interval": [
{
"min": "1",
"max": "10"
}
]
Andersson, et al. Expires 28 November 2026 [Page 50]
Internet-Draft YANG Schema Comparison May 2026
}
}
},
"new": {
"status": "current",
"config": true,
"mandatory": false,
"type": {
"base-type": "string",
"length": {
"interval": [
{
"min": "1",
"max": "20"
}
]
}
}
}
},
{
"node": "/mod:cont/l2",
"node-type": "leaf",
"changed": [
{
"stmt": "node",
"change": "added",
"conformance": "backwards-compatible"
}
],
"new": {
"status": "current",
"config": true,
"mandatory": false,
"type": {
"base-type": "int32"
}
}
}
]
}
]
}
}
<CODE ENDS>
Authors' Addresses
Andersson, et al. Expires 28 November 2026 [Page 51]
Internet-Draft YANG Schema Comparison May 2026
Per Andersson (editor)
Ionio Systems
Email: per.ietf@ionio.se
Robert Wilton
Cisco Systems, Inc.
Email: rwilton@cisco.com
Michal Vaško
CESNET
Email: mvasko@cesnet.cz
Andersson, et al. Expires 28 November 2026 [Page 52]