[oslc-core] Question on query access to link properties

[Ian Green1]

At today's core meeting we discussed properties on links.  Properties on
links are expressed in the RDF model by reified triples.   Here's an
example RM resource:

<RDF>
  <Requirement rdf:about="http://doors.example.com/object/77">
    <implementedBy rdf:resource="http://rtc.example.com/workitem/99"
                             rdf:ID="link1" />
  </Requirement>
  <Description rdf:about="link1">
    <title>WorkItem 99: cache result sets for 5 minutes</title>
    <acme:justifiedBy rdf:resource="http://doors.example.com/module/44"/>
  </Description>
</RDF>


The intent here is that there is an implementation relationship between
requirement 77 and workitem 99, and that relation has a couple of
properties, title and justifiedBy.

Question.  This came up on the call but we wanted to hear Arthur's view in
particular on querying over link properties.  Such properties need to be
accessible to query.  Let's say I was looking for all resources having an
implementedBy link with a justification. Would this be expressed as

oslc.where=implementedBy=*{acme:justifiedBy=*}

Or is there a problem with this - for example, is it ambiguous?

Another worry was that since the RDF/XML above is just one of the ways in
which the RDF model can be presented, would/should OSLC Query support those
additional "surface" representations?  (For example, OSLC query involving
rdf:subject, predicate, and object.  I tried to write such an OSLC query
but gave up - is it possible?)

The feeing on the call was that there ought to be a single recommended way
(perhaps the only way) of accessing link properties in a query which was
reflective of the intuition that most folk would have, given the above
RDF/XML, or JSON representations.