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

On Sun, Jul 18, 2010 at 12:38 PM, Juan Sequeda <juanfederico@gmail.com>wrote:

> 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.
>

Hopefully we are all on the same page on the following:

The Stem graph with default URIs that Eric presents, are essentially RDF
instances of the OWL putative ontology that gets generated from the
relational schema.

In other words, we are talking about the same thing, but with different
words. Therefore, let's get the semantics straight.. and then we can focus
on the syntax issues (creating uris, etc)

>
> 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
>> >>
>> >>
>> >>
>> >>
>> >
>>
>>
>