Internet DRAFT - draft-lhotka-netmod-ysdl
draft-lhotka-netmod-ysdl
NETMOD Working Group L. Lhotka
Internet-Draft CZ.NIC
Intended status: Standards Track November 30, 2015
Expires: June 2, 2016
YANG Schema Dispatching Language
draft-lhotka-netmod-ysdl-00
Abstract
This document defines YANG Schema Dispatching Language (YSDL). It is
a meta-schema language that allows for combining YANG modules into
any number of schemas, and arranging these schemas in a hierarchical
structure.
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 June 2, 2016.
Copyright Notice
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 2
3. YANG Schema Dispatching Language . . . . . . . . . . . . . . 4
3.1. YSDL Schemas . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Validating Data with YSDL and YANG . . . . . . . . . . . 5
4. YSDL YANG Module . . . . . . . . . . . . . . . . . . . . . . 5
5. Example YSDL Meta-Schema . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
YANG data modelling language [I-D.ietf-netmod-rfc6020bis] assumes
that data trees (configuration and state data) defined in YANG
modules start at the common global root. This means that the global
path of every dara node is fixed as soon as the data node is defined
(for a node defined in a grouping, the path is fixed when the
grouping is used).
Recent data modeling efforts, such as
[I-D.rtgyangdt-rtgwg-device-model] indicate that this arrangement may
be too restrictive. A typical use case is a data model that was
designed for a stand-alone device but later needs to be reused for
logical or virtual devices, and the original data model has to be
grafted as a submodel in a top-level schema describing the
organization of logical/virtual devices.
This document proposes a new minilanguage named YANG Schema
Dispatching Language (YSDL) as a solution to this problem. It is a
meta-schema language that allows for defining multiple schemas
comprising one or more YANG modules, and arrange the schemas in a
hierarchical structure.
As a useful side-effect, it is also possible to use YSDL schemas to
specify a data model for an "anydata" node at run time.
2. Terminology and Notation
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].
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The following terms are defined in [I-D.ietf-netmod-rfc6020bis]:
o action,
o anydata,
o augment,
o container,
o data node,
o data tree,
o identity,
o instance identifier,
o leaf,
o leaf-list,
o list,
o module,
o notification,
o RPC operation,
o schema node.
The term "server" denotes a server of a network management protocol
such as NETCONF [RFC6241] or RESTCONF [I-D.ietf-netconf-restconf].
A simplified graphical representation of the data model is used in
this document. The meaning of the symbols in these diagrams is as
follows:
o Brackets "[" and "]" enclose list keys.
o Curly braces "{" and "}" contain names of optional features that
make the corresponding node conditional.
o Abbreviations before data node names: "rw" means configuration
(read-write), "ro" state data (read-only), "-x" RPC operations,
and "-n" notifications.
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o Symbols after data node names: "?" means an optional node, "!" a
container with presence, and "*" denotes a "list" or "leaf-list".
o Parentheses enclose choice and case nodes, and case nodes are also
marked with a colon (":").
o Ellipsis ("...") stands for contents of subtrees that are not
shown.
3. YANG Schema Dispatching Language
The YSDL syntax is defined in Section 4 using YANG in the role of a
schema language. YSDL meta-schemas can be serialized in any encoding
supported by YANG, such as XML [I-D.ietf-netmod-rfc6020bis] or
JSON [I-D.ietf-netmod-yang-json].
YSDL meta-schemas are intended to be used in conjunction with YANG
Library [I-D.ietf-netconf-yang-library]: names and revisions of YANG
modules appearing in a meta-schema SHALL be resolved from YANG
Library data, and YANG Library specifications of supported features
and deviations MUST also be taken into account.
A YSDL meta-schema only affects the main data tree (configuration and
state data), including actions. RPC operations and notifications are
handled exactly as specified in [I-D.ietf-netmod-rfc6020bis].
YANG tree diagram for a YSDL meta-schema is as follows:
module: ietf-ysdl
+--rw schemas
+--rw top-schema? schema-ref
+--rw schema* [name]
+--rw name string
+--rw yang-modules* yang:yang-identifier
+--rw subschema* [root]
+--rw root schema-node-path
+--rw schemas* schema-ref
3.1. YSDL Schemas
A YSDL meta-schema defines one or more schemas, each comprising one
or more YANG modules and zero or more subschemas. The same YANG
module can be part of multiple schemas.
Exactly one of the schemas MUST be the top-level schema which is
identified by the "top-schema" leaf. The top-level schema defines
the uppermost structure of the entire data model, and its root always
coincides with the global root.
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Any schema can define other schemas as its subschema. For each
subschema, the root node has to be specified. Any "container",
"list", "case" or "anydata" schema node contained in one of the
parent schema modules can act as the root node.
Note that the traditional arrangement of YANG modules in a data model
can be achieved with a YSDL meta-schema in which all modules are
listed in the top-level schema, and no subschemas are defined.
3.2. Validating Data with YSDL and YANG
The schema tree of a subschema is conceptually attached to the parent
schema tree as a subtree of the root node. In other words, the first
data node that is either the subschema root or its ancestor coincides
with the conceptual root of the subschema data tree.
All paths (in leafrefs, instance-identifiers, XPath expressions and
target nodes of augments) are interpreted within the subschema data
or schema tree. Therefore, they cannot refer to nodes in the
ancestor schemas or other subschemas.
4. YSDL YANG Module
The "ietf-ysdl" module below defines the YSDL meta-schema language
using YANG. However, it is not meant to be implemented as datastore
contents by a server.
<CODE BEGINS> file "ietf-ysdl@2015-11-30.yang"
module ietf-ysdl {
namespace "urn:ietf:params:xml:ns:yang:ietf-ysdl";
prefix "ysdl";
import ietf-yang-types {
prefix "yang";
}
organization
"IETF NETMOD (NETCONF Data Modeling Language) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netmod/>
WG List: <mailto:netmod@ietf.org>
WG Chair: Thomas Nadeau
<mailto:tnadeau@lucidvision.com>
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WG Chair: Juergen Schoenwaelder
<mailto:j.schoenwaelder@jacobs-university.de>
WG Chair: Kent Watsen
<mailto:kwatsen@juniper.net>
Editor: Ladislav Lhotka
<mailto:lhotka@nic.cz>";
description
"This module defines YANG Schema Dispatching Language (YSDL) - a
meta-schema language for YANG-based data models.
A YSDL schema allows for embedding a YANG schema as a subschema
in a specific location of another module.
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).
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
'OPTIONAL' in the module text are to be interpreted as described
in RFC 2119 (http://tools.ietf.org/html/rfc2119).
This version of this YANG module is part of RFC XXXX
(http://tools.ietf.org/html/rfcXXXX); see the RFC itself for
full legal notices.";
revision 2015-11-30 {
description
"Initial revision.";
reference
"RFC XXXX: YANG Schema Dispatching Language";
}
/* Typedefs */
typedef schema-node-path {
type string {
pattern "[a-zA-Z_][a-zA-Z0-9\\-_.]*:[a-zA-Z_][a-zA-Z0-9\\-_.]*"
+ "(/([a-zA-Z_][a-zA-Z0-9\\-_.]*"
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+ ":)?[a-zA-Z_][a-zA-Z0-9\\-_.]*)";
}
description
"Intra-schema path to a YANG schema node.
The value is a sequence of schema node names separated by the
slash character ('/'). The first (leftmost) component is
prefixed with the name of the YANG module in which the schema
node is defined. A subsequent component has the module prefix
if and only if the preceding schema node is defined in another
module.";
}
typedef schema-ref {
type leafref {
path "/ysdl:schemas/ysdl:schema/ysdl:name";
}
description
"Reference to a schema.";
}
/* YSDL */
container schemas {
description
"Container for YSDL schemas.";
leaf top-schema {
type schema-ref;
description
"Reference to the top-level schema.";
}
list schema {
key "name";
min-elements "1";
description
"Each entry is a named schema. Exactly one entry must be the
top-level schema, other (optional) entries can be used as
subschemas.";
leaf name {
type string;
description
"Name of the schema.";
}
leaf-list yang-modules {
type yang:yang-identifier;
min-elements "1";
description
"Each entry is the name of a YANG module contributing to
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the schema.";
}
list subschema {
key "root";
description
"Each entry is a subschema attached to the parent
schema.";
leaf root {
type schema-node-path;
description
"Each entry specifies the relative (intra-schema) path to
the root node where the subschema is attached. The
schema node MUST be one of: container, list, case or
anydata.
The absolute path of the root node depends on the
structure of schemas:
- For the top-level schema, the root is always '/'.
- For other schemas, the root path is formed by
concatenation of the corresponding root paths of all
ancestor schemas.";
}
leaf-list schemas {
type schema-ref;
description
"References to schemas that comprise the subschema.";
}
}
}
}
}
<CODE ENDS>
5. Example YSDL Meta-Schema
The following YANG module will be used for the top-level schema. It
is a simplified analogy of the "network-device" module from
[I-D.rtgyangdt-rtgwg-device-model].
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module example-device {
namespace "http://www.example.net/example-device";
prefix "exdev";
container device {
container logical-NEs {
list logical-NE {
key "name";
leaf name {
type string;
}
}
}
}
}
The YSDL meta-schema is as follows:
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{
"ietf-ysdl:schemas": {
"top-schema": "device",
"schema": [
{
"name": "device",
"yang-modules": [
"example-device"
],
"subschema": [
{
"root": "example-device:device",
"schemas": [
"if-ip",
"system"
]
},
{
"root": "example-device:device/logical-NEs/logical-NE",
"schemas": [
"if-ip"
]
}
]
},
{
"name": "if-ip",
"yang-modules": [
"ietf-interfaces",
"ietf-ip"
]
},
{
"name": "system",
"yang-modules": [
"ietf-system"
]
}
]
}
}
Apart prom the top-level schema, "device", the meta-schema defines
two other schemas:
o "if-ip" schema consists of "ietf-interfaces" and "ietf-ip"
modules;
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o "system" schema consist of "ietf-system" module.
Two subschemas of the top-level schema defined with the following
root nodes:
o "example-device:device",
o "example-device:device/logical-NEs/logical-NE".
The former one uses both "if-ip" and "system" schemas whereas the
latter uses only "system".
The entire schema tree consisting of the top-level schema and the two
subschemas is shown schematically in the following tree diagram:
module: example-device
+--rw device
+--rw if:interfaces
| ...
+--ro if:interfaces-state
| ...
+--rw sys:system
| ...
+--rw sys:system-state
+--rw logical-NEs
+--rw logical-NE* [name]
+--rw name string
+--rw if:interfaces
| ...
+--ro if:interfaces-state
| ...
6. IANA Considerations
RFC Editor: In this section, replace all occurrences of 'XXXX' with
the actual RFC number and all occurrences of the revision date below
with the date of RFC publication (and remove this note).
This document registers a URI in the "IETF XML registry" [RFC3688].
Following the format in RFC 3688, the following registration has been
made.
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---------------------------------------------------------------------
URI: urn:ietf:params:xml:ns:yang:ietf-ysdl
Registrant Contact: The NETMOD WG of the IETF.
XML: N/A, the requested URI is an XML namespace.
---------------------------------------------------------------------
This document registers a YANG module in the "YANG Module Names"
registry [RFC6020].
---------------------------------------------------------------------
name: ietf-ysdl
namespace: urn:ietf:params:xml:ns:yang:ietf-ysdl
prefix: ysdl
reference: RFC XXXX
---------------------------------------------------------------------
7. Security Considerations
TBD
8. Acknowledgements
YSDL was loosely inspired by Namespace-based Validation Dispatching
Language (NVDL) [ISO.19757-4].
9. References
9.1. Normative References
[I-D.ietf-netconf-yang-library]
Bierman, A., Bjorklund, M., and K. Watsen, "YANG Module
Library", draft-ietf-netconf-yang-library-02 (work in
progress), October 2015.
[I-D.ietf-netmod-rfc6020bis]
Bjorklund, M., "The YANG 1.1 Data Modeling Language",
draft-ietf-netmod-rfc6020bis-08 (work in progress),
October 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
DOI 10.17487/RFC3688, January 2004,
<http://www.rfc-editor.org/info/rfc3688>.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
the Network Configuration Protocol (NETCONF)", RFC 6020,
DOI 10.17487/RFC6020, October 2010,
<http://www.rfc-editor.org/info/rfc6020>.
9.2. Informative References
[I-D.ietf-netconf-restconf]
Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", draft-ietf-netconf-restconf-08 (work in
progress), October 2015.
[I-D.ietf-netmod-yang-json]
Lhotka, L., "JSON Encoding of Data Modeled with YANG",
draft-ietf-netmod-yang-json-06 (work in progress), October
2015.
[I-D.rtgyangdt-rtgwg-device-model]
Lindem, A., Berger, L., Bogdanovic, D., and C. Hopps,
"Network Device YANG Organizational Model", draft-
rtgyangdt-rtgwg-device-model-01 (work in progress),
September 2015.
[ISO.19757-4]
International Organization for Standardization, "Document
Schema Definition Languages (DSDL) - Part 4: Namespace-
based Validation Dispatching Language (NVDL)", ISO/IEC
19757-4, June 2006.
[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,
<http://www.rfc-editor.org/info/rfc6241>.
Author's Address
Ladislav Lhotka
CZ.NIC
Email: lhotka@nic.cz
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