Network Working Group A. Bierman Internet-Draft YumaWorks Updates: 8340 (if approved) M. Bjorklund Intended status: Standards Track Cisco Expires: January 16, 2020 K. Watsen Watsen Networks July 15, 2019 YANG Data Structure Extensions draft-ietf-netmod-yang-data-ext-04 Abstract This document describes YANG mechanisms for defining abstract data structures with YANG. 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 January 16, 2020. Copyright Notice Copyright (c) 2019 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 extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Bierman, et al. Expires January 16, 2020 [Page 1] Internet-Draft YANG Structure July 2019 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. NMDA . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1.2. YANG . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. YANG Data Structures in YANG Tree Diagrams . . . . . . . . . 4 4. YANG Data Structure Extensions Module . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 5.1. YANG Module Registry . . . . . . . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 11 Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 11 A.1. "structure" Example . . . . . . . . . . . . . . . . . . . 11 A.2. "augment-structure" Example . . . . . . . . . . . . . . . 13 A.3. XML Encoding Example . . . . . . . . . . . . . . . . . . 13 A.4. JSON Encoding Example . . . . . . . . . . . . . . . . . . 14 A.5. "structure" example that defines a non-top-level structure . . . . . . . . . . . . . . . . . . . . . . . . 14 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 15 B.1. v02 to v03 . . . . . . . . . . . . . . . . . . . . . . . 15 B.2. v01 to v02 . . . . . . . . . . . . . . . . . . . . . . . 15 B.3. v00 to v01 . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix C. Open Issues . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction There is a need for standard mechanisms to allow the definition of abstract data that is not intended to be implemented as configuration or operational state. The "yang-data" extension statement from RFC 8040 [RFC8040] was defined for this purpose but it is limited in its functionality. The intended use of the "yang-data" extension was to model all or part of a protocol message, such as the "errors" definition in the YANG module "ietf-restconf" [RFC8040], or the contents of a file. However, protocols are often layered such that the header or payload portions of the message can be extended by external documents. The YANG statements that model a protocol need to support this extensibility that is already found in that protocol. The "yang-data" extension from [RFC8040] has been copied here, renamed to "structure", and updated to be more flexible. There is no Bierman, et al. Expires January 16, 2020 [Page 2] Internet-Draft YANG Structure July 2019 assumption that a YANG data structure can only be used as a top-level abstraction, instead of nested within some other data structure. This document also defines a new YANG extension statement called "augment-structure", which allows abstract data structures to be augmented from external modules, similar to the existing YANG "augment" statement. Note that "augment" cannot be used to augment a YANG data structure since a YANG compiler or other tool is not required to understand the "structure" extension. 1.1. Terminology 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. The following terms are used within this document: o YANG data structure: A data structure defined with the "structure" statement. 1.1.1. NMDA The following terms are defined in the Network Management Datastore Architecture (NMDA) [RFC8342]. and are not redefined here: o configuration o operational state 1.1.2. YANG The following terms are defined in [RFC7950]: o absolute-schema-nodeid o container o data definition statement o data node o leaf o leaf-list Bierman, et al. Expires January 16, 2020 [Page 3] Internet-Draft YANG Structure July 2019 o list 2. Definitions A YANG Data Structure is defined with the "structure" extension statement, defined in the YANG module "ietf-yang-structure-ext". The argument to the "structure" extension statement is the name of the data structure. The data structures are considered to be in the same identifier namespace as defined in section 6.2.1 of [RFC7950]. In particular, bullet 7: All leafs, leaf-lists, lists, containers, choices, rpcs, actions, notifications, anydatas, and anyxmls defined (directly or through a "uses" statement) within a parent node or at the top level of the module or its submodules share the same identifier namespace. This means that data structures defined with the "structure" statement cannot have the same name as sibling nodes from regular YANG data definition statements or other "structure" statements in the same YANG module. This does not mean a YANG data structure has to be used as a top- level protocol message or other top-level data structure. 3. YANG Data Structures in YANG Tree Diagrams A YANG Data Structure can be printed in a YANG Tree Diagram [RFC8340]. This document updates RFC 8340 by defining two new sections in the tree diagram for a module: 1. YANG data structures, offset by two spaces and identified by the keyword "structure" followed by the name of the YANG data structure and a colon (":") character. 2. YANG data structure augmentations, offset by 2 spaces and identified by the keyword "augment-structure" followed by the augment target structure name and a colon (":") character. The new sections, including spaces conventions is: Bierman, et al. Expires January 16, 2020 [Page 4] Internet-Draft YANG Structure July 2019 structure : +-- +-- | +-- +-- structure : +-- augment-structure : +-- +-- | +-- +-- augment-structure : +-- 4. YANG Data Structure Extensions Module RFC Ed.: update the date below with the date of RFC publication and remove this note. file "ietf-yang-structure-ext@2019-03-07.yang" module ietf-yang-structure-ext { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext"; prefix sx; organization "IETF NETMOD (NETCONF Data Modeling Language) Working Group"; contact "WG Web: WG List: Author: Andy Bierman Author: Martin Bjorklund Author: Kent Watsen "; description "This module contains conceptual YANG specifications for defining abstract data structures. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', Bierman, et al. Expires January 16, 2020 [Page 5] Internet-Draft YANG Structure July 2019 '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. Copyright (c) 2019 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 Simplified BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info)."; // RFC Ed.: update the date below with the date of RFC publication // and remove this note. revision 2019-03-07 { description "Initial revision."; // RFC Ed.: replace XXXX with RFC number and remove this note reference "RFC XXXX: YANG Structure Extensions."; } extension structure { argument name { yin-element true; } description "This extension is used to specify a YANG data structure that represents conceptual data defined in YANG. It is intended to describe hierarchical data independent of protocol context or specific message encoding format. Data definition statements within a 'structure' extension statement specify the generic syntax for the specific YANG data structure, whose name is the argument of the 'structure' extension statement. Note that this extension does not define a media-type. A specification using this extension MUST specify the message encoding rules, including the content media type, if applicable. The mandatory 'name' parameter value identifies the YANG data structure that is being defined. This extension is only valid as a top-level statement, i.e., given as a sub-statement to 'module' or 'submodule'. Bierman, et al. Expires January 16, 2020 [Page 6] Internet-Draft YANG Structure July 2019 The sub-statements of this extension MUST follow the ABNF rules below, where the rules are defined in RFC 7950: *must-stmt [status-stmt] [description-stmt] [reference-stmt] *(typedef-stmt / grouping-stmt) *data-def-stmt A YANG data structure defined with this extension statement is encoded in the same way as an 'anydata' statement. This means that the name of the structure is encoded as a 'container', with the instantiated child statements encoded as child nodes to this node. The module name and namespace value for the YANG module using the extension statement is assigned to each of the data definition statements resulting from the YANG data structure. The XPath document element is the extension statement itself, such that the child nodes of the document element are represented by the data-def-stmt sub-statements within this extension. This conceptual document is the context for the following YANG statements: - must-stmt - when-stmt - path-stmt - min-elements-stmt - max-elements-stmt - mandatory-stmt - unique-stmt - ordered-by - instance-identifier data type The following data-def-stmt sub-statements are constrained when used within a 'structure' extension statement. - The list-stmt is not required to have a key-stmt defined. - The config-stmt is ignored if present. "; } extension augment-structure { argument path { yin-element true; } Bierman, et al. Expires January 16, 2020 [Page 7] Internet-Draft YANG Structure July 2019 description "This extension is used to specify an augmentation to YANG data structure defined with the 'structure' statement. It is intended to describe hierarchical data independent of protocol context or specific message encoding format. This statement has almost the same structure as the 'augment-stmt'. Data definition statements within this statement specify the semantics and generic syntax for the additional data to be added to the specific YANG data structure, identified by the 'path' argument. The mandatory 'path' parameter value identifies the YANG conceptual data node that is being augmented, represented as an absolute-schema-nodeid string, where the first node in the absolute-schema-nodeid string identifies the YANG data structure to augment, and the rest of the nodes in the string identifies the node within the YANG structure to augment. This extension is only valid as a top-level statement, i.e., given as a sub-statement to 'module' or 'submodule'. The sub-statements of this extension MUST follow the ABNF rules below, where the rules are defined in RFC 7950: [status-stmt] [description-stmt] [reference-stmt] 1*(data-def-stmt / case-stmt) The module name and namespace value for the YANG module using the extension statement is assigned to instance document data conforming to the data definition statements within this extension. The XPath document element is the augmented extension statement itself, such that the child nodes of the document element are represented by the data-def-stmt sub-statements within the augmented 'structure' statement. The context node of the 'augment-structure' statement is derived in the same way as the 'augment' statement, as defined in section 6.4.1 of [RFC7950]. This conceptual node is considered the context node for the following YANG statements: - must-stmt - when-stmt - path-stmt Bierman, et al. Expires January 16, 2020 [Page 8] Internet-Draft YANG Structure July 2019 - min-elements-stmt - max-elements-stmt - mandatory-stmt - unique-stmt - ordered-by - instance-identifier data type The following data-def-stmt sub-statements are constrained when used within an 'augment-structure' extension statement. - The list-stmt is not required to have a key-stmt defined. - The config-stmt is ignored if present. Example: module foo { import ietf-yang-structure-ext { prefix sx; } sx:structure foo-data { container foo-con { } } } module bar { import ietf-yang-structure-ext { prefix sx; } import foo { prefix foo; } sx:augment-structure /foo:foo-data/foo:foo-con { leaf add-leaf1 { type int32; } leaf add-leaf2 { type string; } } } "; } } 5. IANA Considerations 5.1. YANG Module Registry This document registers one URI as a namespace in the "IETF XML Registry" [RFC3688]: URI: urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace. Bierman, et al. Expires January 16, 2020 [Page 9] Internet-Draft YANG Structure July 2019 This document registers one YANG module in the "YANG Module Names" registry [RFC6020]: name: ietf-yang-structure-ext namespace: urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext prefix: sx // RFC Ed.: replace XXXX with RFC number and remove this note reference: RFC XXXX 6. Security Considerations This document defines YANG extensions that are used to define conceptual YANG data structures. It does not introduce any new vulnerabilities beyond those specified in YANG 1.1 [RFC7950]. 7. References 7.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [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, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, . Bierman, et al. Expires January 16, 2020 [Page 10] Internet-Draft YANG Structure July 2019 7.2. Informative References [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, . 7.3. URIs [1] https://github.com/netmod-wg/yang-data-ext/issues Appendix A. Examples A.1. "structure" Example This example shows a simple address book that could be stored as an artifact. Bierman, et al. Expires January 16, 2020 [Page 11] Internet-Draft YANG Structure July 2019 module example-module { yang-version 1.1; namespace "urn:example:example-module"; prefix exm; import ietf-yang-structure-ext { prefix sx; } sx:structure address-book { list address { key "last first"; leaf last { type string; description "Last name"; } leaf first { type string; description "First name"; } leaf street { type string; description "Street name"; } leaf city { type string; description "City name"; } leaf state { type string; description "State name"; } } } } Below is the tree diagram of this module. module: example-module structure address-book: +-- address* [last first] +-- last string +-- first string +-- street? string +-- city? string +-- state? string Bierman, et al. Expires January 16, 2020 [Page 12] Internet-Draft YANG Structure July 2019 A.2. "augment-structure" Example This example adds "county" and "zipcode" leafs to the address book: module example-module-aug { yang-version 1.1; namespace "urn:example:example-module-aug"; prefix exma; import ietf-yang-structure-ext { prefix sx; } import example-module { prefix exm; } sx:augment-structure "/exm:address-book/exm:address" { leaf county { type string; description "County name"; } leaf zipcode { type string; description "Postal zipcode"; } } } Below is the tree diagram of this module. module: example-module-aug augment-structure /exm:address-book/exm:address: +-- county? string +-- zipcode? string A.3. XML Encoding Example This example shows how an address book can be encoded in XML: Bierman, et al. Expires January 16, 2020 [Page 13] Internet-Draft YANG Structure July 2019
Flintstone Fred 301 Cobblestone Way Bedrock 70777
A.4. JSON Encoding Example This example shows how an address book can be encoded in JSON: "example-module:address-book": { "address": [ { "city": "Bedrock", "example-module-aug:zipcode": "70777", "first": "Fred", "last": "Flintstone", "street": "301 Cobblestone Way" } ] } A.5. "structure" example that defines a non-top-level structure The following example defines a data structure with error information, that can be included in an element in an . module example-error-info { yang-version 1.1; namespace "urn:example:example-error-info"; prefix exei; import ietf-yang-structure-ext { prefix sx; } sx:structure my-example-error-info { leaf error-code { type uint32; } } } Bierman, et al. Expires January 16, 2020 [Page 14] Internet-Draft YANG Structure July 2019 The example below shows how this structure can be used in an . protocol operation-failed error 42 Appendix B. Change Log RFC Ed.: remove this section before publication. B.1. v02 to v03 o added YANG tree diagram syntax o added more examples B.2. v01 to v02 o terminology fixes (use the term "structure" instead of "template") o renamed the statement to "structure" from "yang-data" o removed limitations on if-feature and identities in YANG structures B.3. v00 to v01 o moved open issues to github o added examples section o filled in IANA considerations Bierman, et al. Expires January 16, 2020 [Page 15] Internet-Draft YANG Structure July 2019 Appendix C. Open Issues RFC Ed.: remove this section before publication. The YANG Data Structure Extensions issues are tracked on github.com: https://github.com/netmod-wg/yang-data-ext/issues [1] Authors' Addresses Andy Bierman YumaWorks Email: andy@yumaworks.com Martin Bjorklund Cisco Email: mbj@tail-f.com Kent Watsen Watsen Networks Email: kent+ietf@watsen.net Bierman, et al. Expires January 16, 2020 [Page 16]