[OASIS Issue Tracker] (ODATA-849) Add possibility for enumeration types to "extend" another enumeration type

[ https://issues.oasis-open.org/browse/ODATA-849?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Ralf Handl updated ODATA-849:
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    Summary: Add possibility for enumeration types to "extend" another enumeration type  (was: Add possibility for enumeration types to "extend" other enumerations)

> Add possibility for enumeration types to "extend" another enumeration type
> --------------------------------------------------------------------------
>
>                 Key: ODATA-849
>                 URL: https://issues.oasis-open.org/browse/ODATA-849
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: New Feature
>          Components: OData CSDL
>    Affects Versions: V4.0_ERRATA02
>         Environment: [Proposed]
>            Reporter: Michael Pizzo
>            Priority: Minor
>             Fix For: V4.01_WD01
>
>
> [Alternative to ODATA-494]
> We currently don't have a way for adding values to an enumeration type defined by a different schema. This would be helpful for defining custom vocabularies that extend base vocabularies. 
> However, defining inheritance for enumerations introduces substitutability that is likely to break clients by returning new enumeration values not anticipated by the client (for instance, in a switch statement). 
> An alternative to inheritance would be to introduce the ability for an enumeration type to *definitionally* extend an existing enumeration type. This is similar to what we do with entity containers, which can extend the definition of an existing container without introducing any substitutability. 
> We could even use the same "Extends" attribute, rather than "BaseType" which implies inheritance. 



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