Re: What do the ontologists want

>"Peter F. Patel-Schneider" wrote:
>
> > [...]
> > I think that Pat has precisely characterised the situation.
> > There have been numerous posts on this group extolling the virtues of
> > reification.  Many times I think that I am listening to late-night
> > infomercial:
> >
> >         Reification---it chops, it slices, it dices.  No language should be
> >         without it.  No language needs more than it.  Get yours now.  Easy
> >         payment terms of just endless hours of frustration from now to
> >         eternity.
> >
> >         [Only partly in jest.]
>
>Despite all due frustration, reification offers a simple mechanism to
>address several important modeling capabilities heavily used in almost
>all but trivial applications. Let me remind you of some of them using
>examples of some important tasks:
>
>- aggregation: pull out a complete description of a book, incl. authors,
>     affiliation etc. from a dataset containing multiple book
>descriptions.
>     Need to know where to prune the graph.
>
>- ordering: find the first author of a given book.
>
>- nesting: attach a digital signature to a set of statements.

None of these need reification. If they need RDFeification in RDF 
says something about RDF, not about reification. Think, how would you 
do these things in LISP or Python or C++? You would build a suitable 
data structure. What has that got to do with reification?

>- quotation: enough of it on this list...
>
>RDF folks seem in a tough stance trying to satisfy both XML folks and
>logic folks. XML folks want a data structure, and have very pragmatic
>and application-centric requirements. Logic folks want a logical
>language with well-defined semantics. While this balance is extremely
>hard to find,

What on earth are you talking about? It is trivial to find. It has 
been found by everyone who has ever implemented a logical reasoner, 
or an interpreter or parser for any programming language with a 
recursive syntax. Here, in a fourth-echelon state university, we 
teach it to our undergraduates.

>reification is one of the few mechanisms I'm aware of that
>looks like a data structure instrument (admittedly, a clumsy one), but
>is amenable to forging a logical interpretation around it (which might
>not be quite elegant either).

That is exactly what it does NOT do. It actively prevents that being 
done adequately, and gets in the damn way when you try to do it. This 
is not hard to do, if you don't get your datastructuring primitives 
mixed up with your logical syntax. This is EASY. It has probably been 
done successfully thousands of times. There is no deep problem here, 
and so we don't need to search for  a solution to it. We just need to 
be competent.

>I have serious difficulties in explaining to developers why they should
>give up aggregation, ordering, and nesting that come "for free" with
>XML, and turn to RDF instead. I have really hard times finding
>satisfactory representations for these features in RDF, both from the
>perspective of programming convenience and model-theoretic
>interpretation. Maybe reification is a wrong hammer for those nails? If
>so, can anyone criticizing reification suggest a more suitable mechanism
>for handling the aforementioned features that makes both programmers and
>logicians happy?

This is not hard to do. One could use any of the many (probably 
hundreds?) of notions of syntax, for example. As I have said 
repeatedly, I like McCarthy's idea of 'abstract syntax'- basically, 
treating syntactic structure as a term algebra without specifying the 
exact surface forms of the strings used to indicate the structures - 
but almost anything that allows nontrivial structure to be described 
could be used. Expressions can have subexpressions, is the basic 
point. The structure that encodes the relationship of expressions to 
their subexpressions is syntax. If you want to be able to say 
nontrivial things, you will need some nontrivial syntax. (You really 
will, there is no way round it.) Just don't get the encoding of 
syntactic structure mixed up with what the semantics interprets the 
syntax to be saying. Squint your eyes a bit so you can see the forest 
instead of just the triples.

Pat Hayes

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Received on Thursday, 17 May 2001 19:51:53 UTC