| Network Working Group | V. Vassilev |
| Internet-Draft | Transpacket |
| Intended status: Standards Track | June 12, 2015 |
| Expires: December 14, 2015 |
YANG Direct Must Augment Extension
draft-vassilev-netmod-yang-direct-must-augment-ext-00
This document introduces new YANG extension statement for assignment of must sub-statements to existing data nodes through augment without the requirement for a parent data node containing the must statement.
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Copyright (c) 2015 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 (http://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.
The possibility to introduce new sub-statements to existing data nodes available in YANG [RFC6020] provides great flexibility to the authors of data models. However not all sub-statements can be added to existing data nodes through augment. It is not possible to add new must sub-statements. In certain use cases this limitation complicates the task of expressing valid data constraints as must statements. This document explains the problem Section 1.2 and proposes a solution Section 1.3.
The keywords "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].
The following terms are defined in [RFC6020]:
A simplified graphical representation of the data model is used in this document. The meaning of the symbols in these diagrams is as follows:
This document attempts to address the problem YANG model authors encounter when expressing valid data constraints with must statements and wish to use existing model data node as context node for the Xpath expression. The problem is significant in the cases where the context data node has to be evaluated as part of a relative path expressions using . or current(). An example where this problem is encountered is the design of entertainment facility data model. The existing model defines a list of facilities. Each with identity leaf and list of visitors. The authors task is to design a model for a casino and a zoo. For the casino he only needs to define the identity and a constraint for the visitors to be adults older then 18. For the zoo except the identity definition he has to define a constraint that allows only children with adult supervision to be included in the visitors list.
This document defines a YANG extension of the augment statement - ietf-direct-must-augment-extension:augment. The extension accepts must as sub-statement. The extension enables model authors to specify must statements with context nodes in existing models.
The extension is completely backward-compatible with the current definitions in [RFC6020]. An old YANG parser will ignore any must statements introduced by ietf-direct-must-augment-extension:augment No existing models are affected by the new extension, so its introduction will be transparent to the existing YANG parsers.
module entertainment-facilities-casino {
...
identity casino {
base ef:entertainment-facility-generic;
}
direct-must-augment-ex:augment
"/ef:entertainment-facilities/ef:entertainment-facility" +
"ef:visitor" {
when "../ef:type='ef-casino:casino'";
must "(/people/person[name=current()]/age>=18)" {
error-message
"Only adults are allowed in a casino.";
}
}
}
A YANG extension statement "ietf-direct-must-augment-extension:augment" is introduced in the YANG module in Section 3. Its intended use is to allow must as sub-statement which is not possible with the augment statement defined in [RFC6020]. For example:
RFC Ed.: update the date below with the date of RFC publication and remove this note.
<CODE BEGINS> file "ietf-direct-must-augment-extension@2015-06-12.yang"
module ietf-direct-must-augment-extension {
namespace
"urn:ietf:params:xml:ns:yang:ietf-direct-must-augment-extension";
prefix "direct-must-augment-ex";
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
Editor: Vladimir Vassilev
<mailto:vladimir@transpacket.com>";
description
"This module contains extension of the standard augment statement.
Copyright (c) 2015 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).
This version of this YANG module is part of RFC XXXX; see
the RFC itself for full legal notices.";
// RFC Ed.: replace XXXX with actual RFC number and remove this
// note.
// RFC Ed.: update the date below with the date of RFC publication
// and remove this note.
revision 2015-06-12 {
description
"Initial revision.";
reference
"RFC XXXX: Direct Must Augment Extension";
}
/*
* Extension
*/
extension augment {
argument target;
description
"This extension introduces a direct must augment statement
capable of augmenting existing data nodes with new must
sub-statements.";
}
}
<CODE ENDS>
This document registers a URI in the IETF XML registry [RFC3688]. Following the format in RFC 3688, the following registration is requested:
URI: urn:ietf:params:xml:ns:yang:ietf-direct-must-augment-extension Registrant Contact: The NETMOD WG of the IETF. XML: N/A, the requested URI is an XML namespace.
This document registers 1 YANG module in the YANG Module Names registry [RFC6020].
name: ietf-direct-must-augment-extension
namespace:
urn:ietf:params:xml:ns:yang:ietf-direct-must-augment-extension
prefix: direct-must-augment-ex
// RFC Ed. remove this line and replace XXXX in next line
reference: RFC XXXX
This document does not introduce any new security concerns in addition to those specified in [RFC6020], section 15.
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. |
| [RFC6020] | Bjorklund, M., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, October 2010. |
| [RFC6241] | Enns, R., Bjorklund, M., Schoenwaelder, J. and A. Bierman, "Network Configuration Protocol (NETCONF)", RFC 6241, June 2011. |
| [RFC6991] | Schoenwaelder, J., "Common YANG Data Types", RFC 6991, July 2013. |
| [XSD] | Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second Edition", World Wide Web Consortium Recommendation REC-xmlschema-2-20041028, October 2004. |
The "entertainment‑facilities" YANG module models a collection of people and entertainment-facilities. Each person in the people collection has a name and age. Each entertainment-facility has a name, type and list of visitors referencing entries in the people collection. This example model is the target module for direct must augment extension statements defined in Appendix A.2 and Appendix A.3.
module: entertainment-facilities
+--rw people
| +--rw person* [name]
| +--rw name string
| +--rw age uint32
+--rw entertainment-facilities
+--rw entertainment-facility* [name]
+--rw name string
+--rw type identityref
+--rw visitor* -> /people/person/name
module entertainment-facilities {
namespace "http://example.com/ns/entertainment-facilities";
prefix entertainment-facilities;
organization "Example, Inc.";
contact "support@example.com";
description
"Module used in DIRECT-MUST-AUGMENT-EX example.";
revision 2015-06-12 {
description "Initial version";
}
container people {
description
"Contains all people.";
list person {
key name;
leaf name {
type string;
}
leaf age {
type uint32;
mandatory true;
}
}
}
identity entertainment-facility-generic {
description
"Base identity from which specific" +
"entertainment facility types are derived.";
}
container entertainment-facilities {
description
"Container for all entertainment-facilities information.";
list entertainment-facility {
key name;
leaf name {
type string;
}
leaf type {
type identityref {
base entertainment-facility-generic;
}
mandatory true;
}
leaf-list visitor {
type leafref {
path "/people/person/name";
}
}
}
}
}
module entertainment-facilities-casino {
namespace "http://example.com/ns/entertainment-facilities-casino";
prefix ef-casino;
import ietf-direct-must-augment-extension
{ prefix direct-must-augment-ex; }
import entertainment-facilities { prefix ef; }
organization "Example, Inc.";
contact "support@example.com";
description
"Module used in DIRECT-MUST-AUGMENT-EX example. " +
"Defines entertainment facility of type casino where" +
"only adults are allowed.";
revision 2015-06-12 {
description "Initial version";
}
identity casino {
base ef:entertainment-facility-generic;
}
direct-must-augment-ex:augment
"/ef:entertainment-facilities/ef:entertainment-facility/" +
"ef:visitor" {
when "../ef:type='ef-casino:casino'";
must "(/people/person[name=current()]/age>=18)" {
error-message
"Only adults are allowed in a casino.";
}
}
}
module: entertainment-facilities-zoo
augment /ef:entertainment-facilities/ef:entertainment-facility:
+--rw child-supervision* [child]
+--rw child -> ../../ef:visitor
+--rw adult -> ../../ef:visitor
module entertainment-facilities-zoo {
namespace "http://example.com/ns/entertainment-facilities-zoo";
prefix ef-zoo;
import ietf-direct-must-augment-extension
{ prefix direct-must-augment-ex; }
import entertainment-facilities { prefix ef; }
organization "Example, Inc.";
contact "support@example.com";
description
"Module used in DIRECT-MUST-AUGMENT-EX example. " +
"Defines entertainment facility of type zoo where" +
"no children without adult supervision are allowed.";
revision 2015-06-12 {
description "Initial version";
}
identity zoo {
base ef:entertainment-facility-generic;
}
augment
"/ef:entertainment-facilities/ef:entertainment-facility" {
when "ef:type='ef-zoo:zoo'";
list child-supervision {
key child;
leaf child {
type leafref {
path "../../ef:visitor";
}
must "/people/person[name=current()]/age<=14" {
error-message
"People older then 14 are not children.";
}
}
leaf adult {
mandatory true;
type leafref {
path "../../ef:visitor";
}
must "/people/person[name=current()]/age>=18" {
error-message
"People younger then 18 are not adults.";
}
}
}
}
direct-must-augment-ex:augment
"/ef:entertainment-facilities/ef:entertainment-facility/" +
"ef:visitor" {
when "../ef:type='ef-zoo:zoo'";
must "((../child-supervision[child=current()]) or
(/people/person[name=current()]/age>=14))" {
error-message
"Children without adult supervision are not allowed in a zoo.";
}
}
}