[OASIS Issue Tracker] (ODATA-1071) Nullable Collection Navigation Property

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/ODATA-1071?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=66682#comment-66682 ] 

George Ericson commented on ODATA-1071:
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I agree with the conclusion of ODATA-188.  However, I don't agree that Property and NavigationProperty are completely separate concepts.  Rather the UML model holds and NavigationProperty can be modeled as a UML Property that is a MemberEnd of a UML Association.  The issues in ODATA-188 come down to differences based on the UML Type.

On duplicates, my concern is a non-contained NavigationProperty collection that is sourced from multiple underlying implementations.  These underlying implementations may wind up referencing the same resource.  If the implementation of a GET on that collection is  required to eliminate duplicates, then it would have to cache the entire collection and eliminate duplicates before providing a response.  In the special case of a very large collection, this doesn't seem desirable.

> Nullable Collection Navigation Property
> ---------------------------------------
>
>                 Key: ODATA-1071
>                 URL: https://issues.oasis-open.org/browse/ODATA-1071
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: Bug
>          Components: CSDL JSON , CSDL XML
>    Affects Versions: V4.0_CS02
>            Reporter: George Ericson
>            Assignee: George Ericson
>              Labels: Clarification, Errata
>             Fix For: V4.02_WD01
>
>
> There is the assertion:
> "Nullable MUST NOT be specified for a collection-valued navigation property, a collection is allowed to have zero items."
> A property, regardless of multiplicity consumes a slot in an instance (entity representation).  The slot has a sequence of values, depending on cardinality.  If the slot has no values, then the property is said to be null.  If an entry in a list of values has no value, then that entry is null.  So, you can both have a collection property that is null or a collection property consisting of a list of null values.  After much discussion, the DMTF specified the following for the values of a collection property (i.e. upper bound on multiplicity > 1)
> - NULL: The collection has no specified value.
> - [] : The collection has no elements (I.e. size = 0
> - [ Null ] : The collection has one element specified as having no value
> - [ "" ] : The collection has one element specified as having the empty string
> - [ "x", Null, "y",...] : The collection has multiple elements, some may be specified as having no value.
> The collection representing the list of values is not a separate modeled entity, rather it is a representation of the value list of the property itself.



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