[oslc-core] Requests for unknown or unsupported properties

[Samuel Padgett]

I couldn't find clear guidance on how providers should respond to requests
for unknown properties, for instance in an oslc.properties or oslc.select
parameter. This might be a request for a non-standard property that a
provider doesn't recognize (e.g., http://example.com/ns#customProperty) or
a standard, but optional property not supported by the provider.

An example from the CM domain is state predicates, which are optional
properties on a ChangeRequest resource [1]. How should a provider respond
to these queries if it doesn't support oslc_cm:approved? (I've left the
query parameters unescaped and omitted oslc.prefix for readability.)

http://example.com/bugs/34?oslc.properties=oslc_cm:approved
http://example.com/bugs?oslc.select=oslc_cm:approved
http://example.com/bugs?oslc.where=oslc_cm:approved=true

Either responding with a 400 Bad Request or simply leaving unknown
properties out of the response seem like reasonable choices. I propose we
advise providers to simply leave the unknown properties out of the
response. This way consumers can request optional properties without fear
of running into errors. In the case of the oslc.where query above,
providers might simply return no results.

I suggest we update OSLC Core Spec Selective Property Values [2] and the
query specification [3] with guidance.

[1]
http://open-services.net/bin/view/Main/CmSpecificationV2?sortcol=table;up=#Resource_ChangeRequest
[2]
http://open-services.net/bin/view/Main/OslcCoreSpecification?sortcol=table;table=up;up=#Selective_Property_Values
[3] http://open-services.net/bin/view/Main/OSLCCoreSpecQuery
--
Best Regards,
Samuel Padgett | IBM Rational | spadgett at us.ibm.com