Internet DRAFT - draft-ietf-netmod-yang-tree-diagrams
draft-ietf-netmod-yang-tree-diagrams
Network Working Group M. Bjorklund
Internet-Draft Tail-f Systems
Intended status: Best Current Practice L. Berger, Ed.
Expires: August 12, 2018 LabN Consulting, L.L.C.
February 8, 2018
YANG Tree Diagrams
draft-ietf-netmod-yang-tree-diagrams-06
Abstract
This document captures the current syntax used in YANG module Tree
Diagrams. The purpose of this document is to provide a single
location for this definition. This syntax may be updated from time
to time based on the evolution of the YANG language.
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 http://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 August 12, 2018.
Copyright Notice
Copyright (c) 2018 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Tree Diagram Syntax . . . . . . . . . . . . . . . . . . . . . 3
2.1. Submodules . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Groupings . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. yang-data . . . . . . . . . . . . . . . . . . . . . . . . 6
2.4. Collapsed Node Representation . . . . . . . . . . . . . . 6
2.5. Comments . . . . . . . . . . . . . . . . . . . . . . . . 7
2.6. Node Representation . . . . . . . . . . . . . . . . . . . 7
3. Usage Guidelines For RFCs . . . . . . . . . . . . . . . . . . 8
3.1. Wrapping Long Lines . . . . . . . . . . . . . . . . . . . 8
3.2. Groupings . . . . . . . . . . . . . . . . . . . . . . . . 9
3.3. Long Diagrams . . . . . . . . . . . . . . . . . . . . . . 9
4. YANG Schema Mount Tree Diagrams . . . . . . . . . . . . . . . 10
4.1. Representation of Mounted Schema Trees . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Informative References . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
YANG Tree Diagrams were first published in [RFC6536]. Such diagrams
are used to provided a simplified graphical representation of a data
model and can be automatically generated via tools such as "pyang".
(See <https://github.com/mbj4668/pyang>). This document describes
the syntax used in YANG Tree Diagrams. It is expected that this
document will be updated or replaced as changes to the YANG language,
see [RFC7950], necessitate.
Today's common practice is to include the definition of the syntax
used to represent a YANG module in every document that provides a
tree diagram. This practice has several disadvantages and the
purpose of this document is to provide a single location for this
definition. It is not the intent of this document to restrict future
changes, but rather to ensure such changes are easily identified and
suitably agreed upon.
An example tree diagram can be found in [RFC7223] Section 3. A
portion of which follows:
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+--rw interfaces
| +--rw interface* [name]
| +--rw name string
| +--rw description? string
| +--rw type identityref
| +--rw enabled? boolean
| +--rw link-up-down-trap-enable? enumeration
2. Tree Diagram Syntax
This section describes the meaning of the symbols used in YANG Tree
diagrams.
A full tree diagram of a module represents all elements. It includes
the name of the module and sections for top level module statements
(typically containers), augmentations, rpcs and notifications all
identified under a module statement. Module trees may be included in
a document as a whole, by one or more sections, or even subsets of
nodes.
A module is identified by "module:" followed the module-name. This
is followed by one or more sections, in order:
1. The top-level data nodes defined in the module, offset by 2
spaces.
2. Augmentations, offset by 2 spaces and identified by the keyword
"augment" followed by the augment target node and a colon (":")
character.
3. RPCs, offset by 2 spaces and identified by "rpcs:".
4. Notifications, offset by 2 spaces and identified by
"notifications:".
5. Groupings, offset by 2 spaces, and identified by the keyword
"grouping" followed by the name of the grouping and a colon (":")
character.
6. yang-data, offset by 2 spaces, and identified by the keyword
"yang-data" followed by the name of the yang-data structure and a
colon (":") character.
The relative organization of each section is provided using a text-
based format that is typical of a file system directory tree display
command. Each node in the tree is prefaces with "+--". Schema nodes
that are children of another node are offset from the parent by 3
spaces. Sibling schema nodes are listed with the same space offset
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and, when separated by lines, linked via a vertical bar ("|")
character.
The full format, including spacing conventions is:
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module: <module-name>
+--<node>
| +--<node>
| +--<node>
+--<node>
+--<node>
+--<node>
augment <target-node>:
+--<node>
+--<node>
+--<node>
+--<node>
augment <target-node>:
+--<node>
rpcs:
+--<rpc-node>
+--<rpc-node>
+--<node>
| +--<node>
+--<node>
notifications:
+--<notification-node>
+--<notification-node>
+--<node>
| +--<node>
+--<node>
grouping <grouping-name>:
+--<node>
+--<node>
| +--<node>
+--<node>
grouping <grouping-name>:
+--<node>
yang-data <yang-data-name>:
+--<node>
+--<node>
| +--<node>
+--<node>
yang-data <yang-data-name>:
+--<node>
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2.1. Submodules
Submodules are represented in the same fashion as modules, but are
identified by "submodule:" followed the (sub)module-name. For
example:
submodule: <module-name>
+--<node>
| +--<node>
| +--<node>
2.2. Groupings
Nodes within a used grouping are normally expanded as if the nodes
were defined at the location of the "uses" statement. However, it is
also possible to not expand the "uses" statement, but instead print
the name of the grouping.
For example, the following diagram shows the "tls-transport" grouping
from [RFC7407] unexpanded:
+--rw tls
+---u tls-transport
If the grouping is expanded, it could be printed as:
+--rw tls
+--rw port? inet:port-number
+--rw client-fingerprint? x509c2n:tls-fingerprint
+--rw server-fingerprint? x509c2n:tls-fingerprint
+--rw server-identity? snmp:admin-string
Groupings may optionally be present in the "groupings" section.
2.3. yang-data
If the module defines a "yang-data" structure [RFC8040], these
structures may optionally be present in the "yang-data" section.
2.4. Collapsed Node Representation
At times when the composition of the nodes within a module schema are
not important in the context of the presented tree, sibling nodes and
their children can be collapsed using the notation "..." in place of
the text lines used to represent the summarized nodes. For example:
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+--<node>
| ...
+--<node>
+--<node>
+--<node>
2.5. Comments
Single line comments, starting with "//" (possibly indented) and
ending at the end of the line, may be used in the tree notation.
2.6. Node Representation
Each node in a YANG module is printed as:
<status>--<flags> <name><opts> <type> <if-features>
<status> is one of:
+ for current
x for deprecated
o for obsolete
<flags> is one of:
rw for configuration data
ro for non-configuration data, output parameters to rpcs
and actions, and notification parameters
-w for input parameters to rpcs and actions
-u for uses of a grouping
-x for rpcs and actions
-n for notifications
mp for nodes containing a "mount-point" extension statement
<name> is the name of the node
(<name>) means that the node is a choice node
:(<name>) means that the node is a case node
If the node is augmented into the tree from another module,
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its name is printed as <prefix>:<name>, where <prefix> is the
prefix defined in the module where the node is defined.
<opts> is one of:
? for an optional leaf, choice, anydata or anyxml
! for a presence container
* for a leaf-list or list
[<keys>] for a list's keys
/ for a top-level data node in a mounted module
@ for a top-level data node in a parent referenced module
<type> is the name of the type for leafs and leaf-lists
If the type is a leafref, the type is either printed as
"-> TARGET", where TARGET is the leafref path, with prefixes
removed if possible, or printed as "leafref".
<if-features> is the list of features this node depends on,
printed within curly brackets and a question mark "{...}?"
Arbitrary whitespace is allowed between any of the whitespace
separated fields (e.g., <opts> and <type>). Additional whitespace
may for example be used to column align fields (e.g., within a list
or container) to improve readability.
3. Usage Guidelines For RFCs
This section provides general guidelines related to the use of tree
diagrams in RFCs.
3.1. Wrapping Long Lines
Internet Drafts and RFCs limit the number of characters that may in a
line of text to 72 characters. When the tree representation of a
node results in line being longer than this limit the line should be
broken between <opts> and <type>, or between <type> and <if-feature>.
The new line should be indented so that it starts below <name> with a
white space offset of at least two characters. For example:
notifications:
+---n yang-library-change
+--ro module-set-id
-> /modules-state/module-set-id
Long paths (e.g., leafref paths or augment targets) can be split and
printed on more than one line. For example:
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augment /nat:nat/nat:instances/nat:instance/nat:mapping-table
/nat:mapping-entry:
The previously mentioned "pyang" command can be helpful in producing
such output, for example the notification diagram above was produced
using:
pyang -f tree --tree-line-length 50 ietf-yang-library.yang
When a tree diagram is included as a figure in an Internet Draft or
RFC, "--tree-line-length 69" works well.
3.2. Groupings
If the YANG module is comprised of groupings only, then the tree
diagram should contain the groupings. The 'pyang' compiler can be
used to produce a tree diagram with groupings using the "-f tree --
tree-print-groupings" command line parameters.
3.3. Long Diagrams
Tree diagrams can be split into sections to correspond to document
structure. As tree diagrams are intended to provide a simplified
view of a module, diagrams longer than a page should generally be
avoided. If the complete tree diagram for a module becomes too long,
the diagram can be split into several smaller diagrams. For example,
it might be possible to have one diagram with the data node and
another with all notifications. If the data nodes tree is too long,
it is also possible to split the diagram into smaller diagrams for
different subtrees. When long diagrams are included in a document,
authors should consider whether to include the long diagram in the
main body of the document or in an appendix.
An example of such a split can be found in [RFC7407], where section
2.4 shows the diagram for "engine configuration":
+--rw snmp
+--rw engine
// more parameters from the "engine" subtree here
Further, section 2.5 shows the diagram for "target configuration":
+--rw snmp
+--rw target* [name]
// more parameters from the "target" subtree here
The previously mentioned "pyang" command can be helpful in producing
such output, for example the above example was produced using:
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pyang -f tree --tree-path /snmp/target ietf-snmp.yang
4. YANG Schema Mount Tree Diagrams
YANG Schema Mount is defined in [I-D.ietf-netmod-schema-mount] and
warrants some specific discussion. Schema mount is a generic
mechanism that allows for mounting of one or more YANG modules at a
specified location of another (parent) schema. The specific location
is referred to as a mount point, and any container or list node in a
schema may serve as a mount point. Mount points are identified via
the inclusion of the "mount-point" extension statement as a
substatement under a container or list node. Mount point nodes are
thus directly identified in a module schema definition and can be
identified in a tree diagram as indicated above using the "mp" flag.
In the following example taken from [I-D.ietf-rtgwg-ni-model],
"vrf-root" is a container that includes the "mount-point" extension
statement as part of its definition:
module: ietf-network-instance
+--rw network-instances
+--rw network-instance* [name]
+--rw name string
+--rw enabled? boolean
+--rw description? string
+--rw (ni-type)?
+--rw (root-type)
+--:(vrf-root)
| +--mp vrf-root
4.1. Representation of Mounted Schema Trees
The actual modules made available under a mount point is controlled
by a server and is provided to clients. This information is
typically provided via the Schema Mount module defined in
[I-D.ietf-netmod-schema-mount]. The Schema Mount module supports
exposure of both mounted schema and "parent-references". Parent
references are used for XPath evaluation within mounted modules and
do not represent client-accessible paths; the referenced information
is available to clients via the parent schema. Schema mount also
defines an "inline" type mount point where mounted modules are
exposed via the YANG library module.
While the modules made available under a mount point are not
specified in YANG modules that include mount points, the document
defining the module will describe the intended use of the module and
may identify both modules that will be mounted and parent modules
that can be referenced by mounted modules. An example of such a
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description can be found in [I-D.ietf-rtgwg-ni-model]. A specific
implementation of a module containing mount points will also support
a specific list of mounted and referenced modules. In describing
both intended use and actual implementations, it is helpful to show
how mounted modules would be instantiated and referenced under a
mount point using tree diagrams.
In such diagrams, the mount point should be treated much like a
container that uses a grouping. The flags should also be set based
on the "config" leaf mentioned above, and the mount related options
indicated above should be shown for the top level nodes in a mounted
or referenced module. The following example, taken from
[I-D.ietf-rtgwg-ni-model], represents the prior example with YANG
Routing and OSPF modules mounted, YANG Interface module nodes
accessible via a parent-reference, and "config" indicating true:
module: ietf-network-instance
+--rw network-instances
+--rw network-instance* [name]
+--rw name string
+--rw enabled? boolean
+--rw description? string
+--rw (ni-type)?
+--rw (root-type)
+--:(vrf-root)
+--mp vrf-root
+--ro rt:routing-state/
| +--ro router-id?
| +--ro control-plane-protocols
| +--ro control-plane-protocol* [type name]
| +--ro ospf:ospf
| +--ro instance* [af]
| ...
+--rw rt:routing/
| +--rw router-id?
| +--rw control-plane-protocols
| +--rw control-plane-protocol* [type name]
| +--rw ospf:ospf
| +--rw instance* [af]
| ...
+--ro if:interfaces@
| ...
+--ro if:interfaces-state@
| ...
It is worth highlighting that the OSPF module augments the Routing
module, and while it is listed in the Schema Mount module (or inline
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YANG library) there is no special mount-related notation in the tree
diagram.
A mount point definition alone is not sufficient to identify if the
mounted modules are used for configuration or for non-configuration
data. This is determined by the "ietf-yang-schema-mount" module's
"config" leaf associated with the specific mount point and is
indicated on the top level mounted nodes. For example in the above
tree, when the "config" for the routing module indicates false, the
nodes in the "rt:routing" subtree would have different flags:
+--ro rt:routing/
| +--ro router-id?
| +--ro control-plane-protocols
...
5. IANA Considerations
There are no IANA requests or assignments included in this document.
6. Security Considerations
There is no security impact related to the tree diagrams defined in
this document.
7. Informative References
[I-D.ietf-netmod-schema-mount]
Bjorklund, M. and L. Lhotka, "YANG Schema Mount", draft-
ietf-netmod-schema-mount-08 (work in progress), October
2017.
[I-D.ietf-rtgwg-ni-model]
Berger, L., Hopps, C., Lindem, A., Bogdanovic, D., and X.
Liu, "YANG Network Instances", draft-ietf-rtgwg-ni-
model-05 (work in progress), December 2017.
[RFC6536] Bierman, A. and M. Bjorklund, "Network Configuration
Protocol (NETCONF) Access Control Model", RFC 6536,
DOI 10.17487/RFC6536, March 2012, <https://www.rfc-
editor.org/info/rfc6536>.
[RFC7223] Bjorklund, M., "A YANG Data Model for Interface
Management", RFC 7223, DOI 10.17487/RFC7223, May 2014,
<https://www.rfc-editor.org/info/rfc7223>.
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[RFC7407] Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for
SNMP Configuration", RFC 7407, DOI 10.17487/RFC7407,
December 2014, <https://www.rfc-editor.org/info/rfc7407>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
<https://www.rfc-editor.org/info/rfc8040>.
Authors' Addresses
Martin Bjorklund
Tail-f Systems
Email: mbj@tail-f.com
Lou Berger (editor)
LabN Consulting, L.L.C.
Email: lberger@labn.net
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