- From: Chimezie Ogbuji <ogbujic@ccf.org>
- Date: Fri, 12 Mar 2010 15:10:33 -0500
- To: "Birte Glimm" <birte.glimm@comlab.ox.ac.uk>
- cc: "Ivan Herman" <ivan@w3.org>, "SPARQL Working Group WG" <public-rdf-dawg@w3.org>, "Axel Polleres" <axel.polleres@deri.org>, "Sandro Hawke" <sandro@w3.org>
So as I was taking another pass through the Simple RIF Core section, I noticed a problem that I will need to addressed. In short, without some amount of 'embedding', RIF-Simple entailment will behave in a counter-intiuitive way if there is no correspondence between statements and frames, rdf:type and #. Consider the example below Scoping Graph ------------- _:a rdf:type _:b <> rif:imports <emptyRules> Where emptyRules.rif is an empty document A SPARQL query such as SELECT ?THING ?CLASS { ?THING a ?CLASS } will return nothing! In fact (as I understand it - I'm hoping someone else can confirm this) *all* queries will return nothing with the current language: "A solution mapping μ is a?possible solution [...] such that sk(P(BGP)) are well-formed RDF triples that are RIF-Simple entailed by the?RIF-RDF combination formed from sk(SG) and the?strongly safe?RIF core documents referenced from SG via the rif:imports predicate" As a result of condition 7 for common-RIF-RDF-interpretations <I',I> (where I' is a RIF-BLD semantic structure and I is a simple interpretation), the scoping graph is not satisfiable by such an I in a common-RDF-RDF-interpretation. In particular IEXT(IS(rdf:type)) is *not* equal to the set of all pairs (a,?b) in?Dind?×?Dind (since the latter is an empty set). This condition, along with others requires this correspondence in order for an common RIF-RDF-interpretation to be valid. As a result, the combination will not entail anything and since the answers are defined with respect to RIF-Simple entailment, there will be no answers. The mechanisms in section 9.1.3 Embedding Simple Entailment in the compatibility document provide some tools to address the problem and I'm inclined to re-use them rather than simply refer to that informative section since the goal of embedding (to demonstrate how a RIF-compliant translator without native support for RDF can process RIF-RDF combinations) seems very different from what we are doing here as I understand it. My suggested solution is to form the combination differently: SG' = sk(SG) <merge(R,?R_{simple-core},tr(SG')), SG'> Where merge is the same function that is defined towards the end of 9 of the appendix and tr is the same injective function described in the appendix as well. The difference between how tr is used in 9.1.3 and how it is used here is that nothing will need to be done with BNodes (since they will be replaced with new IRIs by the time the function is evaluated over SG'). R is the same strongly, safe RIF Core document referenced from SG. R_{simple-core} is essentially the same ruleset as R_{Simple} (from 9.1.3) except for the exclusion of the rule involving ## (which is not allowed in the RIF Core syntax anyways). So it is: Forall??x??y (?x[rdf:type ->??y]?:-??x #??y) Forall??x??y (?x #??y?:-??x[rdf:type ->??y]) This effectively ensures that condition 7 is met. So, for our example, merge(R,?R_{simple-core},tr(sk(SG))) becomes Forall??x??y (?x[rdf:type ->??y]?:-??x #??y) Forall??x??y (?x #??y?:-??x[rdf:type ->??y]) <skolem_iri_1>[rdf:type -> <skolem_iri_2> <skolem_iri_1> # <skolem_iri_2> And without the issue of the conditions regarding the correspondence between frames and statements, the subgraph characteristics of simple entailment hold, sk(P({?THING rdf:type ?CLASS})) *will* be RIF-simple entailed, and answers would be provided. Any thoughts before I try to incorporate this? -- Chime =================================== P Please consider the environment before printing this e-mail Cleveland Clinic is ranked one of the top hospitals in America by U.S.News & World Report (2009). Visit us online at http://www.clevelandclinic.org for a complete listing of our services, staff and locations. Confidentiality Note: This message is intended for use only by the individual or entity to which it is addressed and may contain information that is privileged, confidential, and exempt from disclosure under applicable law. If the reader of this message is not the intended recipient or the employee or agent responsible for delivering the message to the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please contact the sender immediately and destroy the material in its entirety, whether electronic or hard copy. Thank you.
Received on Friday, 12 March 2010 20:11:22 UTC