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

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?
>
> 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



> It would be kind of odd to switch styles of semantics.
>
> >
> >>
> >>  This is one of the requirements of our charter, although of course we
> >> want mappings to other vocabularies to be possible. Remember, this can
> >> be
> >> thought of as a two-step process, where the first step is a default
> >> mapping, and then later mappigs (via Datalog rules, RIF, SQL or
> >> whatever)
> >> could then transform
> >>
> >
> > In this simple approach, the predicates are the only things that are
> going
> > to be mapped:
> >
> > ex:name ->foaf:name
> > ....
> >
> > So you could have a system that can automatically generate:
> >
> > Triple(s, "ex:name", name) <- student(s_id, name), generateURI(s_id, s)
> >
> > or the user can write the mapping with the :
> >
> > Triple(s, "foaf:name", name) <- student(s_id, name), generateURI(s_id, s)
> >
> >
> >> Could we take the rules given earlier [2] and then use these to produce
> >> the same effects as Eric's direct mapping proposal? Could someone
> >> specify
> >> this in detail?
> >>
> >>
> > The Database-Instance-Only mapping does that.
> >
> >
> >> Then the default mapping could be seen as a certain default application
> >> of
> >> rules, an application that *can* be changed.
> >>
> >
> > The rules defines the semantics of what needs to be implemented in an
> > application
> >
> >
> >>
> >>            cheers,
> >>                 harry
> >>
> >> [1] http://www.w3.org/2001/sw/rdb2rdf/directGraph/
> >> [2]http://web.ing.puc.cl/~marenas/W3C/mapping_language.txt
> >>
> >>
> >>
> >>
> >
>
>