Re: Direct Mapping

* Juan Sequeda <juanfederico@gmail.com> [2010-09-06 15:36-0500]
> On Mon, Sep 6, 2010 at 3:02 PM, Richard Cyganiak <richard@cyganiak.de>wrote:
> 
> > On 6 Sep 2010, at 20:33, Juan Sequeda wrote:
> >
> >> A RDB2RDF system with a R2RML file will always define a RDF graph.
> >>
> >> So what makes the direct mapping different?
> >>
> >> They way I see it, is that the R2RML file is generated automatically, and
> >> with this file, given a RDB2RDF system, you will have a RDF graph. If
> >> other
> >> see it different (I can tell that Eric does), then please shout out.
> >>
> >
> >
> > The goal of the direct mapping is to have a simple, canonical RDF graph
> > representation of every possible database (let's call it the “direct
> > graph”).
> >
> > There are two ways how you could define the direct mapping:
> >
> > 1. As a mapping from a database to a direct graph
> >
> > 2. As a mapping from a database to an R2RML file that maps the database to
> > the direct graph
> >
> > I would prefer the first option, because it better supports the
> > specification of RDB2RDF mappings using generic RDF-to-RDF transformation
> > technologies such as RIF, SPARQL CONSTRUCT, R2R, and so on. If the direct
> > mapping is specified as the first option, then RDB2RDF mappings can be
> > written using these technologies as a mapping from the direct graph to the
> > desired target RDF schema/vocabulary.
> >
> 
> Both options involve presenting the direct mapping rules for the mapping
> from RDB to a direct RDF. Option 2 simply represents this mapping in R2RML.

Let's see if I understand the implied mechanics. Option 1 directly
specifies the RDF graph implied by a database (for any tuple in the
database, you can say exactly what triples are in the direct
graph). Option 2 specifies a mapping language, with certain mapping
semantics, and with a default configuration. The default graph is the
products of applying the mapping semantics for a default configuration
to a database.


> So you think that a direct mapping shouldn't output the R2RML file? I think
> it should because this file is the basis for people to work on and start
> customizing it.

The RDF rules folks will have everything they need with option 1. They
can write/share rules in RIF, SPIN, n3, ... which transform the
default graph to popular ontologies. Simple implementations will
materialize these graphs, and arguably cooler implementations will
work directly on the relational data, but that's really implementation
detail; all they need is the default graph.


> > Hence I'm with Eric here.
> >
> >
> >  The automatic mapping file that is generated in D2R is equivalent to the
> >> Direct Mapping (right Richard?).
> >>
> >
> > Well I'd say the *graph* produced by an auto-generated D2R mapping file is
> > equivalent to the direct mapping.
> >
> 
> and I'd call the auto-generated D2R mapping file the Direct Mapping file. So
> D2R does option 2 then.
> 
> >
> > Best,
> > Richard

-- 
-ericP

Received on Monday, 6 September 2010 21:46:31 UTC