[oslc-cm] State Predicates

[Samuel Padgett]

The current spec language around state predicates is unclear. The
ChangeRequest resource [1] lists them as optional properties. The state
predicates section [2] of the spec says that they MUST be queryable,
however, which seems to imply that they aren't optional. I suggest we
update the spec to say,

"Predicates are exposed as OPTIONAL single-value properties on a Change
Request resource, often read-only. An attempt to update read-only
predicates SHOULD be answered with a 409 Conflict HTTP status code. Their
presence in a resource representation used for an update via PUT MUST NOT
prevent the resource from being updated. If present, predicates MUST be
queryable. The Change Request resource definition sections defines the
complete set of predicates."

There is a second issue of how consumers know if a CM provider supports
state predicates. They can't rely on resource shapes since shapes are
optional. It's also not clear how providers should respond to requests for
state predicates when they're not supported. I've raised this latter
problem as a possible core issue since I couldn't find guidance on how
providers should respond to requests for any unsupported properties. [3]

[1]
http://open-services.net/bin/view/Main/CmSpecificationV2?sortcol=table;up=#Resource_ChangeRequest
[2]
http://open-services.net/bin/view/Main/CmSpecificationV2?sortcol=table;up=#State_Predicates
[3]
http://open-services.net/pipermail/oslc-core_open-services.net/2012-March/001256.html
--
Best Regards,
Samuel Padgett | IBM Rational | spadgett at us.ibm.com