Network Working Group P. Andersson, Ed. Internet-Draft Ionio Systems Updates: 7950 (if approved) R. Wilton Intended status: Standards Track Cisco Systems, Inc. Expires: 19 August 2026 M. Vaško CESNET 15 February 2026 YANG Schema Comparison draft-ietf-netmod-yang-schema-comparison-06 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 the 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 19 August 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 19 August 2026 [Page 1] Internet-Draft YANG Schema Comparison February 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. Compiled YANG schema tree . . . . . . . . . . . . . . . . . . 4 4. YANG schema tree comparison algorithm . . . . . . . . . . . . 5 4.1. Module identification . . . . . . . . . . . . . . . . . . 5 4.2. Change content . . . . . . . . . . . . . . . . . . . . . 6 4.3. Change conformance . . . . . . . . . . . . . . . . . . . 6 4.4. Compiled and parsed schema changes . . . . . . . . . . . 6 5. Comparison tooling . . . . . . . . . . . . . . . . . . . . . 7 6. Schema Comparison YANG Module . . . . . . . . . . . . . . . . 7 7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 39 8. Security Considerations . . . . . . . . . . . . . . . . . . . 40 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 9.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 40 9.2. The "YANG Module Names" Registry . . . . . . . . . . . . 41 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 10.1. Normative References . . . . . . . . . . . . . . . . . . 41 10.2. Informative References . . . . . . . . . . . . . . . . . 43 Appendix A. Comparison Examples . . . . . . . . . . . . . . . . 43 A.1. Relaxed Range Module . . . . . . . . . . . . . . . . . . 43 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 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. 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. Andersson, et al. Expires 19 August 2026 [Page 2] Internet-Draft YANG Schema Comparison February 2026 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 gNMI. 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 This document uses the following terminology introduced in the YANG versioning requirements document [I-D.ietf-netmod-yang-versioning-reqs]: * Backwards-compatible: TODO * Non-backwards-compatible: TODO Andersson, et al. Expires 19 August 2026 [Page 3] Internet-Draft YANG Schema Comparison February 2026 3. Compiled YANG 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 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 * typedef * grouping * augment * deviation Andersson, et al. Expires 19 August 2026 [Page 4] Internet-Draft YANG Schema Comparison February 2026 * feature * if-feature * refine * extension 4. 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. 4.1. 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. Andersson, et al. Expires 19 August 2026 [Page 5] Internet-Draft YANG Schema Comparison February 2026 4.2. 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. 4.3. Change conformance Every change is classified as either backwards-compatible or non- backwards-compatible based on sections 3.1.1 and 3.1.2 in [I-D.ietf-netmod-yang-module-versioning]. But, there are cases when it is impossible for tooling to determine whether a change is backwards-compatible or not. The affected statements are: * pattern * when * must * description * extension instance Normally, any change in these statement is reported as non-backwards- compatible. However, if the author of the new revision of a YANG module determines that the change of an aforementioned statement is backwards-compatible based on the compatibility rules for the specific statement, they can decide to use the 'schema-cmp:backwards- compatible' extension to signify this fact. Then, this change must be reported as backwards-compatible. 4.4. 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. Andersson, et al. Expires 19 August 2026 [Page 6] Internet-Draft YANG Schema Comparison February 2026 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. 5. 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. 6. Schema Comparison YANG Module YANG module with nodes describing the differences between two revisions of YANG schemas. The "ietf-yang-schema-comparison" 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]. file "ietf-yang-schema-comparison@2026-02-11.yang" module ietf-yang-schema-comparison { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison"; prefix schema-cmp; 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"; } organization "IETF NETMOD (Network Modeling) Working Group"; contact "WG List: NETCONF WG list Andersson, et al. Expires 19 August 2026 [Page 7] Internet-Draft YANG Schema Comparison February 2026 WG Web: https://datatracker.ietf.org/wg/netmod Author: Michal Vaško Author: Rob Wilton Author: Per Andersson "; description "This YANG 1.1 module contains definitions and extensions to support comparison between different versions of YANG schemas. The output of the comparison algorithm is described in this YANG module. 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 // remove this note. revision 2026-02-11 { description "Initial revision."; Andersson, et al. Expires 19 August 2026 [Page 8] Internet-Draft YANG Schema Comparison February 2026 reference "RFC XXXX: YANG Schema Comparison"; } extension backwards-compatible { description "Marks statements in a new revision of a module that were changed but in a backwards-compatible manner according to YANG 1.1 and 1.0 rules for updating a module. When used as a substatement of a 'pattern' statement, it means its allowed value space has been expanded. When used as a substatement of a 'when' or 'must' statement, it means their constraint has been relaxed. When used as a substatement of a 'description' statement, it means it has been changed in a backwards-compatible way. When used as a substatement of an extension instance, it means adding, modifying, or removing it is a backwards-compatible change. The same is true for any substatements of the extension instance. Not allowed to be instantiated for any other 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"; } 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"; } Andersson, et al. Expires 19 August 2026 [Page 9] Internet-Draft YANG Schema Comparison February 2026 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'."; } 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" { Andersson, et al. Expires 19 August 2026 [Page 10] Internet-Draft YANG Schema Comparison February 2026 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'."; } 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" { Andersson, et al. Expires 19 August 2026 [Page 11] Internet-Draft YANG Schema Comparison February 2026 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'."; } 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 Andersson, et al. Expires 19 August 2026 [Page 12] Internet-Draft YANG Schema Comparison February 2026 "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'."; } 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 Andersson, et al. Expires 19 August 2026 [Page 13] Internet-Draft YANG Schema Comparison February 2026 "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."; 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."; } } Andersson, et al. Expires 19 August 2026 [Page 14] Internet-Draft YANG Schema Comparison February 2026 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" { 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; } Andersson, et al. Expires 19 August 2026 [Page 15] Internet-Draft YANG Schema Comparison February 2026 } grouping when-stmts { description "Describes changes of all the must 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."; } 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 { Andersson, et al. Expires 19 August 2026 [Page 16] Internet-Draft YANG Schema Comparison February 2026 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'."; } 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'."; } Andersson, et al. Expires 19 August 2026 [Page 17] Internet-Draft YANG Schema Comparison February 2026 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'."; } 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 { Andersson, et al. Expires 19 August 2026 [Page 18] Internet-Draft YANG Schema Comparison February 2026 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 "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 { Andersson, et al. Expires 19 August 2026 [Page 19] Internet-Draft YANG Schema Comparison February 2026 type boolean; 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 { if-feature parsed-schema; } 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; } 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."; Andersson, et al. Expires 19 August 2026 [Page 20] Internet-Draft YANG Schema Comparison February 2026 } 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; } 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."; } Andersson, et al. Expires 19 August 2026 [Page 21] Internet-Draft YANG Schema Comparison February 2026 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 "Range argument substatement value."; } 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 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; Andersson, et al. Expires 19 August 2026 [Page 22] Internet-Draft YANG Schema Comparison February 2026 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; } 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."; Andersson, et al. Expires 19 August 2026 [Page 23] Internet-Draft YANG Schema Comparison February 2026 } 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; } 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 { Andersson, et al. Expires 19 August 2026 [Page 24] Internet-Draft YANG Schema Comparison February 2026 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."; } 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; Andersson, et al. Expires 19 August 2026 [Page 25] Internet-Draft YANG Schema Comparison February 2026 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; description "Presence substatement existence."; } 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."; Andersson, et al. Expires 19 August 2026 [Page 26] Internet-Draft YANG Schema Comparison February 2026 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 "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; Andersson, et al. Expires 19 August 2026 [Page 27] Internet-Draft YANG Schema Comparison February 2026 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."; } 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; Andersson, et al. Expires 19 August 2026 [Page 28] Internet-Draft YANG Schema Comparison February 2026 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; 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 { Andersson, et al. Expires 19 August 2026 [Page 29] Internet-Draft YANG Schema Comparison February 2026 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 "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."; Andersson, et al. Expires 19 August 2026 [Page 30] Internet-Draft YANG Schema Comparison February 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."; } list unique { description "List of unique substatements."; 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; } } Andersson, et al. Expires 19 August 2026 [Page 31] Internet-Draft YANG Schema Comparison February 2026 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; 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 { Andersson, et al. Expires 19 August 2026 [Page 32] Internet-Draft YANG Schema Comparison February 2026 enum "backwards-compatible" { description "Backwards-compatible or editorial change."; } enum "non-backwards-compatible" { description "Non-backwards-compatible change."; } } mandatory true; description "Conformance information of a change in the compared YANG modules."; } } 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" { Andersson, et al. Expires 19 August 2026 [Page 33] Internet-Draft YANG Schema Comparison February 2026 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 "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."; Andersson, et al. Expires 19 August 2026 [Page 34] Internet-Draft YANG Schema Comparison February 2026 } } 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."; } 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" { Andersson, et al. Expires 19 August 2026 [Page 35] Internet-Draft YANG Schema Comparison February 2026 description "YANG statement 'augment' node."; } enum "refine" { description "YANG statement 'refine' node."; } enum "typedef" { description "YANG statement 'typedef'."; } } mandatory true; description "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" { Andersson, et al. Expires 19 August 2026 [Page 36] Internet-Draft YANG Schema Comparison February 2026 description "YANG statement 'container' node."; } enum "leaf" { description "YANG statement 'leaf' node."; } enum "leaf-list" { description "YANG statement 'leaf-list' node."; } enum "list" { 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 { Andersson, et al. Expires 19 August 2026 [Page 37] Internet-Draft YANG Schema Comparison February 2026 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 { 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 { Andersson, et al. Expires 19 August 2026 [Page 38] Internet-Draft YANG Schema Comparison February 2026 description "Changed statements in the newer revision of the YANG module."; uses module-substmts; } } uses parsed-info { if-feature parsed-schema; } uses node-info; } } } 7. 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 Andersson, et al. Expires 19 August 2026 [Page 39] Internet-Draft YANG Schema Comparison February 2026 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. 8. Security Considerations This section follows the template defined in Section 3.7.1 of [RFC8407]. 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. 9. IANA Considerations 9.1. 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: Andersson, et al. Expires 19 August 2026 [Page 40] Internet-Draft YANG Schema Comparison February 2026 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. 9.2. The "YANG Module Names" Registry This document registers one YANG module 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 registration is requested: Name: ietf-yang-schema-comparison XML Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-schema-comparison Prefix: schema-cmp Reference: RFC XXXX 10. References 10.1. 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-15, 18 October 2025, . [I-D.ietf-netmod-yang-packages] Wilton, R., Rahman, R., Clarke, J., and J. Sterne, "YANG Packages", Work in Progress, Internet-Draft, draft-ietf- netmod-yang-packages-06, 7 July 2025, . [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- 24, 29 September 2025, . Andersson, et al. Expires 19 August 2026 [Page 41] Internet-Draft YANG Schema Comparison February 2026 [I-D.ietf-netmod-yang-versioning-reqs] Clarke, J., "YANG Module Versioning Requirements", Work in Progress, Internet-Draft, draft-ietf-netmod-yang- versioning-reqs-13, 18 January 2026, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC6991] Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Andersson, et al. Expires 19 August 2026 [Page 42] Internet-Draft YANG Schema Comparison February 2026 [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K., and R. Wilton, "YANG Library", RFC 8525, DOI 10.17487/RFC8525, March 2019, . [RFC8791] Bierman, A., Björklund, M., and K. Watsen, "YANG Data Structure Extensions", RFC 8791, DOI 10.17487/RFC8791, June 2020, . 10.2. 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, . Appendix A. 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. A.1. Relaxed Range Module An example module comparison with a typedef range restriction relaxed and a new leaf added. Andersson, et al. Expires 19 August 2026 [Page 43] Internet-Draft YANG Schema Comparison February 2026 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. 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; } } } Andersson, et al. Expires 19 August 2026 [Page 44] Internet-Draft YANG Schema Comparison February 2026 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; } } } 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 19 August 2026 [Page 45] Internet-Draft YANG Schema Comparison February 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 19 August 2026 [Page 46] Internet-Draft YANG Schema Comparison February 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" } } } ] } ] } } Authors' Addresses Andersson, et al. Expires 19 August 2026 [Page 47] Internet-Draft YANG Schema Comparison February 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 19 August 2026 [Page 48]