



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



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   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.












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   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




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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




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   *  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.






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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.











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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.













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   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






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   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



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                 <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



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          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";
     }



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   }
   <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].





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   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.









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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>.







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   [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>.




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   [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";



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     }

     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



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     // 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'.";
         }



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         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'.";
         }



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         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'.";
         }



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         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'.";
         }



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         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.";



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       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 {



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             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.";
         }



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         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'.";
           }



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           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'.";
           }



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           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



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               "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 {



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           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;



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       }
       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 {



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         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;



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       }
       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;
     }



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     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.";



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       }
       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;



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         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



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             "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.";
       }



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       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;



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           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



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             "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.";



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             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;



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       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.";
       }
     }



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     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



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         "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.";



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         }
         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



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             "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 {



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               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 {



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         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;



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       }
     }
   }
   <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>







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   <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": [
                 {



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                   "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"
                       }
                     ]



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                   }
                 }
               },
               "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




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   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






































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