Re: Relationship between EricP's default mapping and Datalog rules approach?

On Sun, Jul 18, 2010 at 5:31 PM, Eric Prud'hommeaux <eric@w3.org> wrote:
> * Juan Sequeda <juanfederico@gmail.com> [2010-07-18 12:38-0500]
>> On Sun, Jul 18, 2010 at 12:23 PM, Harry Halpin <hhalpin@w3.org> wrote:
>>
>> > > Harry,
>> > >
>> > > On Sun, Jul 18, 2010 at 8:26 AM, Harry Halpin <hhalpin@w3.org> wrote:
>> > >
>> > >> While I enjoyed the talk last week, I was wondering about the
>> > >> relationship
>> > >> between Eric's proposed direct mapping [1] and the rules put forward
>> > >> last
>> > >> week by Marcelo [2]. This question goes to both, and the entire working
>> > >> group.
>> > >>
>> > >> One of the advantages of Eric's default mapping mechanism [1] is that it
>> > >> allows relational data to be expressed in RDF without the author of the
>> > >> mapping knowing *any* rules or having any ontology that he or she wants
>> > >> to
>> > >> map their relational data to.
>> > >>
>> > >
>> > > This is exactly the same as the Database-Instance-Only mapping.
>> >
>> > Are we sure? Eric - thoughts?
>
> The main goal of http://www.w3.org/2001/sw/rdb2rdf/directGraph/ was to
> precisely define the default graph. If the document is successful, an
> implementor should be able to take a relational database and a stem
> URI and create a (virtual) direct graph.
>
>> > There's at least two differences I see. Syntactically, ericP is not
>> > generating any new predicate URIs (foaf:name), thus his insistence on
>> > creating a "stem graph" with default URIs. I imagine this will just be a
>> > simple option, with the generateURIs being created by a call to some
>> > standardized interface to the Linked Data Web via a search engine like
>> > Sindice, a vocabulary management service, or something like OKKAM.
>> >
>> >
>> I think this is an issue of the syntax. A predicate needs to be created.
>> This is the semantics. How it's going to be done is another issue.
>>
>> The second difference is how Eric decided to express his semantics, i.e.
>> > using sets rather than Datalog-ish rules that resemble FOL. I went over
>> > Eric's work only once, but I believe we need to make a decision as a
>> > Working Group to pick one style of doing semantics and stick with it in
>> > the spec, even though they are technically equivalent, i.e. we should
>> > choose between set-theoretic model theory or just a mapping to
>> > FOL/Datalog/RIF semantics with a standard interpretation.
>> >
>>
>> Honestly, I have trouble understanding the semantics that Eric has written.
>>
>> I would recommend using Datalog because
>>
>> 1) it has well defined semantics
>> 2) it can be translated to RIF
>> 3) it can be translated to SQL
>
> I eventually picked set semantics because of the success of "Semantics
> and Complexity of SPARQL" Pérez, Arenas, and Gutierrez
>  http://arxiv.org/pdf/cs.DB/0605124
>
> This is a good opportunity for me to proof-read and provide an English
> reading, using the definitions in the Notation section:

I am also having trouble reading Eric's document. In my opinion, the
default mapping language should be a simple language, but Eric's
specification looks complicated. I think it would help us if Eric
could give a presentation about the document in the conference call
(showing how the approach works in a concrete example).

Received on Monday, 19 July 2010 18:22:28 UTC