Internet DRAFT - draft-bierman-netmod-yang-data-ext
draft-bierman-netmod-yang-data-ext
Network Working Group A. Bierman
Internet-Draft YumaWorks
Intended status: Standards Track M. Bjorklund
Expires: May 3, 2018 Tail-f Systems
K. Watsen
Juniper Networks
October 30, 2017
YANG Data Extensions
draft-bierman-netmod-yang-data-ext-01
Abstract
This document describes YANG mechanisms for defining abstract data
structures with YANG. It is intended to replace and extend the
"yang-data" extension statement defined in RFC 8040.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 3, 2018.
Copyright Notice
Copyright (c) 2017 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
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include Simplified BSD License text as described in Section 4.e of
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.1. NMDA . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. YANG . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Restrictions on Conceptual YANG Data . . . . . . . . . . 4
2.2. YANG Data Extensions Module . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
3.1. YANG Module Registry . . . . . . . . . . . . . . . . . . 9
4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. Normative References . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 9
A.1. v00 to v01 . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix B. Open Issues . . . . . . . . . . . . . . . . . . . . 9
B.1. uses-yang-data . . . . . . . . . . . . . . . . . . . . . 10
B.2. error-info . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
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] is defined for this purpose, however it is limited in
its functionality.
The intended use of the "yang-data" extension is to model all or part
of a protocol message, such as the "errors" definition in ietf-
restconf.yang [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.
This document defines a new YANG extension statement called
"augment-yang-data", 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 "yang-data" extension.
The "yang-data" extension from [RFC8040] has been copied here and
updated to be more flexible. There is no longer a requirement for
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the "yang-data" statement to result in exactly one container object.
There is no longer an assumption that a yang data structure can only
be used as a top-level abstraction, instead of nested within some
other data structure.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The following terms are used within this document:
o yang data structure: A data structure defined with the "yang-data"
statement.
1.1.1. NMDA
The following terms are defined in the Network Management Datastore
Architecture (NMDA) [I-D.ietf-netmod-revised-datastores]. 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
o list
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2. Definitions
2.1. Restrictions on Conceptual YANG Data
This document places restrictions on the "yang-data" external
statements that can be used with the "yang-data" and
"augment-yang-data" extensions. The conceptual data definitions 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 conceptual data defined with the "yang-data" or
"augment-yang-data" statements cannot have the same local-name as
sibling nodes from regular YANG data definition statements or other
"yang-data" or "augment-yang-data" statements.
This does not mean a yang data structure has to be used as a top-
level protocol message or other top-level data structure. A yang
data structure does not have to result in a single container.
2.2. YANG Data Extensions Module
The "yang-data-ext" module defines the "augment-yang-data" extension
to augment conceptual data already defined with the "yang-data"
extension. The RESTCONF "yang-data" extension has been moved to this
document and updated.
RFC Ed.: update the date below with the date of RFC publication and
remove this note.
<CODE BEGINS> file "yang-data-ext@2017-10-30.yang"
module yang-data-ext {
// not assigning real module name and namespace unless
// and until changed to a draft-ietf-netmod document
namespace "urn:ietf:params:xml:ns:yang:yang-data-ext";
prefix "yd";
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
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Author: Andy Bierman
<mailto:andy@yumaworks.com>
Author: Martin Bjorklund
<mailto:mbj@tail-f.com>
Author: Kent Watsen
<mailto:kwatsen@juniper.net>";
description
"This module contains conceptual YANG specifications
for defining abstract 'yang-data' data structures.
Copyright (c) 2017 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).";
revision 2017-10-30 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Data Extensions.";
}
extension yang-data {
argument name {
yin-element true;
}
description
"This extension is used to specify a YANG data template which
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 yang-data extension
specify the generic syntax for the specific YANG data
template, whose name is the argument of the yang-data
extension statement.
Note that this extension does not define a media-type.
A specification using this extension MUST specify the
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message encoding rules, including the content media type.
The mandatory 'name' parameter value identifies the YANG
data template that is being defined. It contains the
template name. This parameter is only used for readability
purposes. There are no mechanisms to reuse yang-data by
its template name value.
This extension is ignored unless it appears as a top-level
statement. It MUST contain data definition statements
that result in a set of data definition statements.
If the yang data template is intended to be used as
a top-level structure, then the yang data template needs to
result in a single container, so an instance of the YANG data
template can thus be translated into an XML instance document,
whose top-level element corresponds to the top-level container.
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 template.
The name of each data definition statement resulting from
a yang data template is assigned to a top-level identifier name
in the data node identifier namespace, according to RFC 7950,
section 6.2.1.
The sub-statements of this extension MUST follow the
'data-def-stmt' rule in the YANG ABNF.
The XPath document root is the extension statement itself,
such that the child nodes of the document root 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 yang-data-resource extension statement.
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- The list-stmt is not required to have a key-stmt defined.
- The if-feature-stmt is ignored if present.
- The config-stmt is ignored if present.
- The available identity values for any 'identityref'
leaf or leaf-list nodes is limited to the module
containing this extension statement, and the modules
imported into that module.
";
}
extension augment-yang-data {
argument path {
yin-element true;
}
description
"This extension is used to specify an augmentation to
conceptual data defined with the 'yang-data' 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 template,
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.
This extension is ignored unless it appears as a top-level
statement. The sub-statements of this extension MUST follow
the 'data-def-stmt' rule in the YANG ABNF.
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 root is the augmented extension statement
itself, such that the child nodes of the document root are
represented by the data-def-stmt sub-statements within
the augmented yang-data statement.
The context node of the augment-yang-data statement is derived
in the same way as the 'augment' statement, as defined in
section 6.4.1 of [RFC7950]. This conceptual node is
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considered the context node 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 augment-yang-data extension statement.
- The list-stmt is not required to have a key-stmt defined.
- The if-feature-stmt is ignored if present.
- The config-stmt is ignored if present.
- The available identity values for any 'identityref'
leaf or leaf-list nodes is limited to the module
containing this extension statement, and the modules
imported into that module.
Example:
foo.yang {
import ietf-restconf { prefix rc; }
rc:yang-data foo-data {
container foo-con { }
}
}
bar.yang {
import yang-data-ext { prefix yd; }
import foo { prefix foo; }
yd:augment-yang-data /foo:foo-con {
leaf add-leaf1 { type int32; }
leaf add-leaf2 { type string; }
}
}
";
}
}
<CODE ENDS>
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3. IANA Considerations
3.1. YANG Module Registry
TBD
4. Security Considerations
This document defines YANG extensions that are used to define
conceptual YANG data. It does not introduce any new vulnerabilities
beyond those specified in YANG 1.1 [RFC7950].
5. Normative References
[I-D.ietf-netmod-revised-datastores]
Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
and R. Wilton, "Network Management Datastore
Architecture", draft-ietf-netmod-revised-datastores-05
(work in progress), October 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<http://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<http://www.rfc-editor.org/info/rfc8040>.
Appendix A. Change Log
A.1. v00 to v01
o Added Martin and Kent as authors
o Cloned and updated yang-data from RFC 8040
o Added text to clarify that yang-data does not have to result in a
single container
Appendix B. Open Issues
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B.1. uses-yang-data
Is there a need for a separate grouping and uses mechanism for yang-
data? Currently only real grouping-stmt and uses-stmt are used.
B.2. error-info
Is there a need for a special-purpose extension to define yang-data
for the contents of the <error-info> node in NETCONF <rpc-error> and
RESTCONF <errors> responses? This node is defined with anyxml so
there is no way for a YANG tool to use real schema nodes, based on
the RPC operation being requested or the error-app-tag that is being
returned.
Authors' Addresses
Andy Bierman
YumaWorks
Email: andy@yumaworks.com
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
Kent Watsen
Juniper Networks
Email: kwatsen@juniper.net
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