Overview

The following study describes extending YANG language statements to allow customization of models.

YANG Language

• The YANG language provides us the ability to define and model configurations and state data by defining YANG modules
  • Modules contain a sequence of statements
    • Statement syntax is either of the following :
      • statement = keyword [argument] ;
      • statement = keyword [argument] { <substatement(s)..> } ;

* argument can be zero or one depending on the statement

* argument is a string

• An XML-based equivalent version of YANG is called YIN
• YANG uses a tree to define the hierarchy of data wherein each ‘node’ has a value or/and a set of child nodes
  • 4 types of nodes
    • leaf nodes
    • container nodes
    • leaf-list nodes
    • list nodes

Figure 1.1 Schema tree of module 'stores'

YANG extension Statement

** the YIN version and Schema trees above are generated by YANG validator 'pyang'

Expected tree diagram for example-module based on RFC8340 (https://datatracker.ietf.org/doc/html/rfc8340):

Existing YANG parser

(Please see https://wiki.onap.org/display/DW/Existing+Yang+Parser)

OpenDayLight Yang tools recognises YANG extensions

• Contains interface which has methods to access data of a YANG extension statement

  • package org.opendaylight.yangtools.yang.model.api;
    import org.opendaylight.yangtools.yang.model.api.stmt.ExtensionEffectiveStatement;
    public interface ExtensionDefinition extends SchemaNode, EffectiveStatementEquivalent<ExtensionEffectiveStatement> {
        String getArgument();
        boolean isYinElement();
    }

    • Implementing Class
      • Class

References:

https://datatracker.ietf.org/doc/rfc8526/

https://www.rfc-editor.org/rfc/rfc6095.html

https://www.hjp.at/doc/rfc/rfc6020.html#sec_6.3.1

https://docs.opendaylight.org/en/latest/release-notes/upgrade-process.html?highlight=extension%20annotation#unrecognized-yang-statement-handling

https://datatracker.ietf.org/doc/html/rfc6110#section-9.4

https://datatracker.ietf.org/doc/html/rfc8791