[OASIS Issue Tracker] Commented: (ODATA-12) create a data type for property names

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    [ http://tools.oasis-open.org/issues/browse/ODATA-12?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=31059#action_31059 ] 

Michael Pizzo commented on ODATA-12:
------------------------------------

Random thoughts:  

The reason this is not straightforward is that annotations are defined using the same entity model, and using the same type system, as the schema of the service. So adding a more specific type to the type system for the model element would either make that same type available for all schema usages (i.e., a "Customer" could have a property of type "Property") or cause special rules depending on how a defined type was used.

One way to address this would be to use the built-in extensibility of the type system (the ability to define complex types) to define a core vocabulary containing a type ("OData.Model.Property") that represents a property, and use that type in the vocabulary.

For example:

<Schema Namespace="OData.Model">
  <ComplexType Name="Property">
        <Property Name="PropertyName" Type="String" Nullable="False"/>
  </ComplexType>
  //...
</Schema>

Then we could use it in a definition as:

<Schema Namespace="OData.Temporal">
 
  <ComplexType Name="Period">
        <Property Name="StartPeriod" Type="ODataModel.Property" Nullable="False"/>
        <Property Name="EndPeriod" Type="ODataModel.Property" Nullable="False"/>
   </ComplexType>

   <ValueTerm Name="ApplicationPeriod" Type="Temporal.Period">
   //...
</Schema>

And apply it as:

<TypeAnnotation Term="Temporal.ApplicationPeriod"> 
   <Record Type="Temporal.Period">
      <PropertyValue Name="StartPeriod">
            <Record Type="OData.Model.Property">
                 <PropertyValue Name="PropertyName" String="bus_start" /> 
            </Record>
      </PropertyValue>
      <PropertyValue Name="EndPeriod">
            <Record Type="OData.Model.Property">
                 <PropertyValue Name="PropertyName" String="bus_end" /> 
            </Record>
     </PropertyValue>
   </Record>
</TypeAnnotation> 

It's obviously more verbose than just specifying a "ModelProperty" type, but it does convey the intention without convoluting the type system.  Perhaps we could work on shortcuts for expressing the same semantics as above.

> create a data type for property names
> -------------------------------------
>
>                 Key: ODATA-12
>                 URL: http://tools.oasis-open.org/issues/browse/ODATA-12
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: Improvement
>          Components: OData CSDL v1.0
>            Reporter: Andrew Eisenberg
>            Assignee: Michael Pizzo
>            Priority: Minor
>
> The Edm.String data type can be used to define a type annotation property when the property will hold the name of some other property. A more specific data type could be added to OData for this purpose.
> In the OData Extension for Temporal Data we suggested this annotation:
> <TypeAnnotation Term="Temporal.ApplicationPeriod">
>    <PropertyValue Name="StartPeriod" String="bus_start" />
>    <PropertyValue Name="EndPeriod" String="bus_end" />
> </TypeAnnotation>
> Instead of declaring StartPeriod and EndPeriod to be of type String, we could declare them to be of type PropertyName.

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