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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)..> } ;
...
Sample YANG (stores.yang with extension) | Statements and Description |
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| Code Block |
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| language | yml |
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| title | stores model with extension |
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| linenumbers | true |
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| module sync-enxtensionextension {
…
prefix sync-exext;
…
extension sync-flag{
description
“This is a sample extension statement description“
argument "value";
}
….
}
|
The following model shows that it imported the model above where extensions is declared. | Code Block |
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| language | yml |
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| title | extended-stores model |
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| linenumbers | true |
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| module extended-stores {
yang-version 1.1;
...
import sync-extension{
prefix sync-exext;
}
typedef year {
type uint16 {
range "1000..9999";
}
}
container bookstore {
sync-exext:sync-flag "on";
...
}
}
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| extension Statement see example from Lines 5-9 on stores model with extension | Code Block |
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| extension <keyword/identifier>{
<extension substatements...>
} |
see example from Line 15 on extended-stores model | Code Block |
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| <module prefix>:<extension keyword> "argument"; |
- to be used to define new statements
- available to be imported and used by other modules just like a normal YANG statement
- by use of 'import statement' to import the module where the extension is defined
- statements that do not have any substatements can have extensions defined if wanted
- its only one argument is the identifier and keyword for the extension
- Optional substatements:
- argument Statement
- description Statement
- reference Statement
- defined extension Statements
argument Statement see examples from Line 6 on stores model - takes a string argument which is the name of the argument to the keyword
- Optional substatement
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| Code Block |
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| language | xml |
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| theme | Midnight |
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| title | YIN-extended-stores model |
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| linenumbers | true |
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| <?xml version="1.0" encoding="UTF-8"?>
<module name="extended-stores"
xmlns="urn:ietf:params:xml:ns:yang:yin:1"
xmlns:ext-book-store="org:onap:ccsdk:sampleExtended"
xmlns:book-store="org:onap:ccsdk:sample">
<namespace uri="org:onap:ccsdk:sampleExtended"/>
<prefix value="ext-book-store"/>
<revision date="2020-09-15">
<description>
<text>Sample Extended Model</text>
</description>
</revision>
<import module="storessync-extension">
<prefix value="booksync-storeext"/>
</import>
<typedef name="year">
<type name="uint16">
<range value="1000..9999"/>
</type>
</typedef>
<container name="bookstore">
<book<sync-storeext:sync-flag value="on"/>
<leaf name="bookstore-name">
<type name="string"/>
</leaf>
...
</container>
</module> |
| yin-element Statement - takes a string argument which is true or false
- yin-element is 'false' by default
- if the argument is 'true' it indicates that the argument is mapped to an XML element in YIN or to an XML attribute
Notes - Line 22 on YIN-extended-stores model
- result of using the argument without specifying the yin-element value
- yin-element is 'false'
- the argument 'value' is only an XML attribute
- if argument statement (Line 6 on stores model) contains yin-element substatement YIN-extend-stores model would result to the following:
extension statement will produce a child node | Code Block |
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| theme | Midnight |
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| title | YIN-extended-stores model where yin-element is 'true' |
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| ...
<container name="bookstore">
<book<sync-storeext:sync-flag>
<book<sync-storeext:value>on</booksync-storeext:value>
</booksync-storeext:sync-flag>
...
</container>
... |
** extension does not extend the data
|
** the YIN version and Schema trees above are generated by YANG validator 'pyang'
Existing YANG parser in CPS
(Please see https://wikilf-onap.onapatlassian.orgnet/wiki/display/DW/Existing+Yang+Parser)
OpenDayLight Yang tools recognize YANG extensions
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**Red cell for case number indicates that tests have failed
- the extension is defined as substatement in the module with argument statement as its substatement
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| Case # | Description | Result |
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| 1 | - Created schema set
- the model contained only an extension definition
| - successfully stored yang resource
- successfully created a node using the model
- fragment table did not add the extension argument in attributes
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| 2 | - Created schema set
- the model contained an extension definition and the model was used inside a container node
| - successfully stored yang resource
- successfully created a node using the model
- fragment table did not add the extension argument in attributes
*the same result acquired for all passed cases on the groovy tests table above |
| 3 | - Created schema set
- the model contained only an extension definition
- extension contains argument
| - creating the schema set failed
- received 500 server error parsing schema set
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| 4 | - Created schema set
- the model contained an extension definition and was used inside the container node
- extension contains argument
| - creating the schema set failed
- received 500 server error parsing schema set
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Conclusions
- The YANG language extension analysis above is only applicable for seeing that it is good for type configuration.
- The extension does not extend the actual data of the model instance
- Based on the test scenarios above, extensions can only be seen on the schema sets and not on the data
- YANG extension can be used at every level of the tree model
- The test results show that the model is being recognized by the current YANG tools used to parse a model
- It fails for scenarios such as parsing a model without an argument defined when it is expecting it
- This analysis did not look further into the effect of setting yin-element to 'true' for the model instance
- Further investigation is required to cover interpretation as the analysis above only covers parsing
- see
| Jira Legacy |
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| server | System Jira |
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| serverId | 4733707d-2057-3a0f-ae5e-4fd8aff50176 |
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| key | CPS-866 |
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|