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EARL 1.0 HTTP graph conformance: graphs or things?

From: Dan Connolly <connolly@w3.org>
Date: Tue, 15 Dec 2009 14:50:03 -0600
To: public-earl10-comments@w3.org
Message-ID: <1260910203.3504.6552.camel@pav.lan>
This EARL HTTP-in-RDF stuff is pretty neat; it's clear that
a lot of careful thought has gone into it.

I'm not sure how to read the conformance requirements:

"Graphs conforming to this HTTP-in-RDF specification must meet the
following requirements:

     1. A Connection must have exactly one connection authority"

Do you mean to constrain the syntax or the semantics here?

If you mean to constrain the semantics, a clear way to
say it is:

  Each Connection is related by http:connectionAuthority to
  exactly one thing.

Better yet, use OWL; add this to the schema:

     SubClassOf: http:connectionAuthority exactly 1.

(that's written in OWL manchester syntax; I can
work out the details of how to spell it
in RDF/XML if you clarify that this is what you want.)

Based on that, if we saw:

  :x a http:Connection; http:connectionAuthority :y, :z.

that would not be an error, but it would allow
us to conclude:

  :y owl:sameAs :z.

If you mean to constrain the syntax to prevent the
example above, a clear way to say it is:

  Each term related to http:Connection by rdf:type must
  be related by http:connectionAuthority to exactly one term. 

That becomes a mouthful; I suggest using SPARQL;
say that any graph that gives a "yes" answer
to this query violates the constraint:
  ask {
   ?c a http:Connection.
   ?c http:connectionAuthority ?a1.
   ?c http:connectionAuthority ?a2.
   filter (?a1 != ?a2)

I don't see the value in constraining the syntax; I don't
see how any of your use cases need it. Constraining the
semantics by adding OWL stuff to the schema has all sorts
of valuable uses, on the other hand.

Dan Connolly, W3C http://www.w3.org/People/Connolly/
gpg D3C2 887B 0F92 6005 C541  0875 0F91 96DE 6E52 C29E
Received on Tuesday, 15 December 2009 20:50:12 UTC

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