Re: shapes-ISSUE-18 (S35 examples): S35 needs to state what constraints are required

There is no need for verification in OWL constraints or SPIN for the RDF graph 
under consideration to be connected.  All that OWL constraints and SPIN care 
about is what information is contained in the RDF graph.

Also, neither OWL constraints nor SPIN generally start off with a single node. 
  Instead the processing of a typical constraints (in SPIN the combination of 
a class and a SPIN constraint it is connected to, in OWL constraints an axiom 
of the form class <= description) starts out by finding all the instances of a 
class and then checking them against the body of the constraint.  The body of 
the constraint can only act on the information in the RDF graph, of course, 
but that's what RDF is all about.

As SPIN has the entire power of SPARQL, I think that it is possible to form 
constraints that state things like "if there is an instance of class X then 
there must be an instance of class Y in the graph".  This particular 
constraint is no possible in OWL constraints, however.

peter


On 12/20/2014 01:34 AM, Eric Prud'hommeaux wrote:
>
> On Dec 19, 2014 5:01 AM, "RDF Data Shapes Working Group Issue Tracker"
> <sysbot+tracker@w3.org <mailto:sysbot%2Btracker@w3.org>> wrote:
>  >
>  > shapes-ISSUE-18 (S35 examples): S35 needs to state what constraints are
> required
>  >
>  > http://www.w3.org/2014/data-shapes/track/issues/18
>  >
>  > Raised by: Peter Patel-Schneider
>  > On product:
>  >
>  > S35
> https://www.w3.org/2014/data-shapes/wiki/User_Stories#S35:_Describe_disconnected_graphs
> talks about constraints over disconnected graphs.  However, it does not state
> why disconnected graphs are different from connected graphs?  Are the
> constraints supposed to recognize disconnected graphs?  Or are the constraints
> just supposed to work on disconnected graphs, and what differences in
> constraint handling are required for disconnected graphs.
>  >
>  > SPIN and OWL constraints don't care whether a graph is connected or
> disconnected.
>
> I'm trying to understand this last statement. If I had an OWL CWA/UNA engine,
> I could presumably use something like OWL API to ask if a particular node
> conforms to some class (as a shape) definition. There's no mechanism in OWL
> that would enable that verification process to reach any node not connected to
> that started node. One would simply have to verify both nodes or invent some
> sort of packaging language which would entail both verifications.
>
> Likewise SPIN would depends on essentially separate verification processes
> kicked off by some mechanism to connect the starting nodes to some shapes.
>
> This is essentially a proposed requirement for the mechanism which triggers
> verification/validation (regardless of whether it's used for validation or
> description).
>

Received on Saturday, 20 December 2014 14:44:20 UTC