| 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
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.
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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 (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.
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 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.
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:
The following terms are defined in the Network Management Datastore Architecture (NMDA) [I-D.ietf-netmod-revised-datastores]. and are not redefined here:
The following terms are defined in [RFC7950]:
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.
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>
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
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.
- 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
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>
TBD
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].
| [I-D.ietf-netmod-revised-datastores] | Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K. and R. Wilton, "Network Management Datastore Architecture", Internet-Draft draft-ietf-netmod-revised-datastores-05, October 2017. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC7950] | Bjorklund, M., "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. |
Is there a need for a separate grouping and uses mechanism for yang-data? Currently only real grouping-stmt and uses-stmt are used.
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.