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

George Ericson created ODATA-1071:

             Summary: 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
         Environment: Schema 
            Reporter: George Ericson
            Assignee: George Ericson
             Fix For: V4.01_CSD02

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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