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Subject: RE: instance annotations

There are examples where an annotation is meant to be applied to an instance and not the model that describes the instance.


For example in the Redfish vocabulary there is this:

      <Term Name="Settings" Type="Settings.Settings">

        <Annotation Term="OData.Description" String="The link to the settings resource that represents the settings to apply to this resource."/>



As I understand it, this Term could have been alternatively defined as a ‘Settings’ property of the model that it is applied to.


My preference would be to use instance annotations only as a way to pass information about the underlying Model that an instance is realized from.  If we want to dig deeper, we could ask a representative of the Redfish team to provide more rational.






From: odata@lists.oasis-open.org <odata@lists.oasis-open.org> On Behalf Of Michael Pizzo
Sent: Saturday, February 20, 2021 2:01 PM
To: Christof Sprenger
Cc: odata@lists.oasis-open.org
Subject: [odata] RE: instance annotations



We don't currently have a way to specify that an annotation term is intended for use as an instance annotation – to my recollection, it has never come up.


How would this information be useful to the client?  Is it just a matter of documenting how the term is intended to be used, or is it required at runtime in order to invoke some type of logic?


If it's part of documenting the usage, then we generally try to convey that in the description – having a machine-readable way to determine if a term is intended as an instance annotation is useful if code needs to determine applicability.


For comparison, the AppliesTo attribute for metadata annotations is intended to help schema designers know where they can put what terms (i.e., you can have a drop-down of terms that are applicable to a particular model element without having to understand the semantics of the term.)  AppliesTo is *not* intended to be restrictive (i.e., clients should not throw an error if a term is used somewhere that is not called out in AppliesTo).


Similarly, clients should never error due to an unexpected/unknown instance annotation, so I wouldn't add a way to distinguish a term as intended for an instance annotation in order to add client validation.


From: odata@lists.oasis-open.org <odata@lists.oasis-open.org> On Behalf Of Christof Sprenger
Sent: Thursday, February 18, 2021 2:58 PM
To: odata@lists.oasis-open.org
Subject: [EXTERNAL] [odata] instance annotations




I would have expected to find something in the annotation term applicability table that allows me to specify that an annotation is intended as an instance annotation.


OData Common Schema Definition Language (CSDL) XML Representation Version 4.01 (oasis-open.org)


Am I misunderstanding something how a term is supposed to be defined that can be used as an instance annotation? Or is this a gap in the standard?



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