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Re: On the integration of Topic Maps and RDF

From: Andrei S. Lopatenko <andrei@derpi.tuwien.ac.at>
Date: Wed, 22 Aug 2001 15:50:32 +0200
Message-ID: <01e901c12b11$698707e0$a6498280@tuwien.ac.at>
To: "Leo Obrst" <lobrst@mitre.org>, <pfps@research.bell-labs.com>, <em@w3.org>, <lacher@db.stanford.edu>, <gdm@empolis.co.uk>
Cc: <www-rdf-interest@w3.org>
I completely agree that semantic information must not be lost in
transformation.
But really it was not lost in "object layer" mapping suggested in the
article.
Semantic information about meaning of RDF resources transformed from XTM is
implicitly declared in RDF  graph of resourses
and could be extracted by inference engine. In F-Logic query example
semantic of element is extracted in a such way (roleLabel condition).
So there are several possible ways to map TM into RDF

1 The one is preserving explicit semantic
    XTM ->  RDF Resource graph +  RDF Schema (or DAML+ OIL, OIL)
For example, such classes as country, natural-resource should be defined in
the schema
And then query should be asked using that new terms
...
natural-resource -> pertoleum;
...
2 Another is "object layer"  mapping which just encode XTM graph as a RDF
graph   and semantic is stored implicitly in that graph.
The query should contain statements for extracting semantic information
such in F-Logic  in the article
...
tms:roleLabel->natural-resource;
...
or semantic should be provided by inference engine

But from the point of view of the article  - to develop query engine which
can also include XTM resources into  RDF
both ways are suitable. The difference is only in queries. Information is
not lost.
Maybe, for other applications it is neccesity to have explicitly declared
semantic, bot not for this?

Best regards
MSc Andrei S. Lopatenko
Researcher
Vienna University of Technology
Extension Centre
http://derpi.tuwien.ac.at/~andrei/










----- Original Message -----
From: "Leo Obrst" <lobrst@mitre.org>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: <lacher@db.stanford.edu>; <em@w3.org>; <www-rdf-interest@w3.org>;
<gdm@empolis.co.uk>
Sent: Wednesday, August 22, 2001 2:56 AM
Subject: Re: On the integration of Topic Maps and RDF


> I have to agree with Peter on this. I really can't understand the
> alternative. Unless you really do formalize a third representation
> language which attempts to "preserve" the semantics of the mappings
> between your other two languages (say, with a notion of the formal
> properties represented and preserved on each side through those
> "mappings" or morphisms), then you are spinning in air. Semantic
> interoperability or semantic "mapping" requires a commensurate
> language/model. How else can it work? Modeling the semantics of a model
> in the syntax of another model just can't work. You need to preserve the
> semantics of the original model when you translate it into the syntax of
> the other model (or approximate it to a greater or lesser degree of
> possible formalization).
>
> Leo
>
> "Peter F. Patel-Schneider" wrote:
> >
> > I think that we will have to ``agree to disagree'' on whether mappings
> > between Topic Maps and RDF should preserve meaning.
> >
> > I strongly, no, passionately, believe that such mappings have to be
> > model-mappins that preserve meaning, at least if one is to hold the view
> > that RDF is a representation formalism.  If RDF is a representation
> > formalism, then positive ground binary relations have to be represented
as
> > RDF triples.  Otherwise, RDF is just some syntactic encoding, and the
> > entire meaning is conveyed in some outside-of-RDF (and, probably,
outside of
> > the web) side agreement.
> >
> > Any approach that requires an outside-of-RDF approach to ascribe meaning
to
> > the resulting RDF has, in my opinion, lost everything.  Yes, an approach
> > that stays within RDF has the potential of losing some things, but at
least
> > the portion that can be naturally represented in RDF is completely
> > captured.
> >
> > Peter F. Patel-Schneider
> > Bell Labs Research
> >
> > From: "Martin Lacher" <lacher@db.stanford.edu>
> > Subject: RE: On the integration of Topic Maps and RDF
> > Date: Tue, 21 Aug 2001 11:25:22 -0700
> >
> > > Hi Peter,
> > >
> > > Thank you very much for your comments. Your question concerns a very
> > > important point in the mapping.
> > >
> > > > One important aspect of such mappings, for me, is whether
information
> > > > expressed naturally in the source formalism (Topic Maps) and then
> > > > translated into the target formalism (RDF) can be naturally
> > > > integrated with
> > > > information expressed naturally in the target formalism.  If this is
not
> > > > the case, then I claim that there is something wrong with the
translation.
> > >
> > > You are right, there are several ways to perform such a mapping.
Graham
> > > Moore has nicely summarized the mapping approaches in his paper on
RDF/Topic
> > > Maps. He called the approach you propose "mapping the model" and the
> > > approach we took "modeling the model".
> > > When mapping the model, the semantics of the primitives of one model
have to
> > > be mapped to the semantics of the primitives in the other model. It is
sort
> > > of an all-in-one approach, which attacks the problem in one piece
(i.e.
> > > mapping all semantics of Topic Maps in one piece to all semantics that
RDF
> > > offers). The downside of this approach is that one is likely to incur
loss
> > > in the mapping, since the primitive constructs won't be close enough.
> > > When modeling the model, one model is expressed in the syntax of
another.
> > > The advantage of this approach is, that loss is less likely to be
incurred,
> > > since only the syntax primitives have to be mapped.
> > > As an example, mapping the model one has to map what an association
conveys
> > > in Topic Maps to what a property conveys in RDF. That is virtually
> > > impossible, since associations in Topic Maps are much richer. When
modeling
> > > the model in this case on only has to map what the graph model
primitives in
> > > the Topic Map model convey to what the graph model primitives in RDF
can
> > > convey.
> > > The unifying view on both of the approaches is that modelling the
model is
> > > just again a mapping the model on another layer (see paper of Sergey
Melnik
> > > on layered interoperability model). That means that our graph
translation is
> > > again a mapping of the graph semantics of Topic Maps (which is
expressed in
> > > XTM syntax) to the graph semantics of RDF ( any syntax). However, we
believe
> > > that by performing the mapping between the primitives, we incur less
loss.
> > >
> > > > Suppose some facts about natural resources come from topic maps, and
are
> > > > represented in this translation to RDF, and other facts about
natural
> > > > resources come from a natural RDF representation.  How can one query
the
> > > > RDF to find the union of the facts?  Even if it is possible to
> > > > write a such
> > > > a query is it at all possible to write such a query without knowing
that
> > > > some of the natural resource facts come from topic maps?
> > >
> > > No, the query processor will have to be aware of what source it is
querying.
> > > But that is not a bad thing, since the specifics of the source can be
> > > expressed in a rule language. On top of that rule base one couled
possibly
> > > imagine some universal query laguage. However, the question is,
whether that
> > > is desirable at all - since one would lose all the specifics of the
> > > respective formats. For example, one could possibly not query for a
unique
> > > property in DAML data anymore. Or one could not query for an
association
> > > scope of a Topic Map association anymore. That probably depends on the
> > > application context.
> > >
> > > So the definite advantages of our approach are:
> > > - only (n-1) mappings between formats required instead of n(n-1)/2 for
an
> > > all-capable query engine
> > > - mapping between the higher-level constructs can be expressed
declaratively
> > > - existing RDF infrastructure can be re-used for Topic Maps
> > >
> > > Cheers,
> > >
> > > Martin
>
> --
> _____________________________________________
> Dr. Leo Obrst The MITRE Corporation
> mailto:lobrst@mitre.org Intelligent Information Management/Exploitation
> Voice: 703-883-6770 7515 Colshire Drive, M/S W640
> Fax: 703-883-1379       McLean, VA 22102-7508, USA
>
>
Received on Wednesday, 22 August 2001 09:45:17 GMT

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