Re: relational data as a bona fide member of the SM

N-ary relations work great in a graph model. The only reason they seem
awkward in the Semantic Web world, in my opinion, is that RDF leads us to
looking at a graph *decomposition* instead of an actual assembled graph.
This effect cascades onto SPARQL and OWL, and thus we end up with a great
forest we're reduced to looking at, and talking about, one twig at a time.

glenn


On Friday, November 4, 2011, AzamatAbdoullaev <abdoul@cytanet.com.cy> wrote:
> That's a big issue of Relational Ontology, or "N-Relational Ontology of
Things", as discussed 5 years ago:
> http://lists.w3.org/Archives/Public/semantic-web/2006Apr/0047.html.
> And it is not strange that a consistent formal account of N-Relations has
been long missing. Relations are so ubiquitious and omnipresent that most
people take them for granted. In a general sense, everything is related to
everything. We are related to the world around us, to other people, to our
country, to our family and children and to ourselves. There are
ontological, logical, natural, physical, mechanical, biological,
psychological, emotional, technological, social, cultural, moral,
sexual, aesthetic, and semiotic relations, to name a few. For most people,
there is no particular problem with most of these relations, may be, except
ontological and semiotic (semantic, syntactic and pragmatic) relations.
However, theorists have been perpetually puzzled over relations, and they
have tried to understand them theoretically and systematically,
but consistent, machine-readable models of relations have proved
extraordinarily difficult to construct:
> "What Organizes the World: N-Relational Entities":
http://www.igi-global.com/chapter/reality-universal-ontology-knowledge-systems/28313
>
> What is hardly questionable, to be implemented, the semantic web indeed
requires a unified formal ontology of relations: UFOR.
>
> Azamat Abdoullaev
>
> ----- Original Message -----
> From: Frank Manola
> To: Alexandre Riazanov
> Cc: Semantic Web List
> Sent: Friday, November 04, 2011 1:23 AM
> Subject: Re: relational data as a bona fide member of the SM
>
> On Nov 3, 2011, at 6:22 PM, Alexandre Riazanov wrote:
>
>
> On Thu, Nov 3, 2011 at 5:20 PM, Frank Manola <fmanola@acm.org> wrote:
>
> On Nov 3, 2011, at 3:19 PM, Alexandre Riazanov wrote:
>
> I have been asking this sort of questions for a while and the only decent
answer I know is that
> Description Logics only work with unary and binary predicates (classes
and properties),
> although I believe RDF was initially developed independently from the DL
and OWL work.
>
> RIF and RuleML seem to be going in the relational direction (see also the
earlier work
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.48.7623&rep=rep1&type=pdfby
Harold Boley), but it is difficult to break the monopoly
> of RDF+OWL.
>
> From my point of view, a major reason for focusing on unary and binary
predicates (the logical forms that underlie RDF triples) is that it's
easier to deal with the problems of integrating heterogeneous data (a key
issue in the semantic web) if the data is in (or is mapped to being in)
that form, as opposed to data in arbitrary arity relations (for example,
with n-aries you need a schema to interpret any tuples you encounter "in
the wild", otherwise you don't know what the "columns" mean).  If you go
back to the period before the "monopoly of RDF+OWL"  :-)  and look at the
work on integrating heterogeneous relational databases, one of the major
approaches to developing the mappings between the various relational
schemas was by interpreting the various local schemas in terms of unary and
binary relations for just this reason (compound keys had to be dealt with
in this way too, because the same combinations of columns didn't
necessarily constitute the keys in otherwise corresponding relations in the
different local schemas).   Mind you, if you're NOT worried about
integrating heterogeneous data, RDF introduces extra pain of its own
(figuring out all those identifiers, for one thing), but if you ARE worried
about integrating heterogenous data, I think you want those identifiers
around.
>
> I don't quite understand your argument. Indeed, interoperability is the
target. Syntactic interoperability is not a problem as long as you use the
same or convertible syntaxes.
> Semantic interoperability requires shared understanding of the
identifiers being used, which has nothing to do with arity. Reinterpreting
legacy relational schemas is a related, but separate issue.
> Binary predicates are often handy to represent attributes, but it does
not mean n-ary predicates cannot be helpful in the same (although I could
not recall a real example) and other KR tasks.
>
> Let me try again, then (although I can't guarantee I'll be any more
understandable this time!).  The original question (I thought) was why
there weren't relational approaches applied in Semantic-Web-like contexts
(where, as you say, interoperability is the target).  I cited the
integration of heterogeneous relational databases to argue that, in this
case, where relations were already being used by all parties, and
interoperability was the target, those doing the integration found that
using unaries and binaries helped (I agree that shared understanding of the
identifiers is necessarily for semantic interoperability, but in RDF+OWL,
at least the identifiers are *there*;  those putting the data on the Web
had to create them).   All that RDF is doing is starting from the unaries
and binaries.  This is not an argument that n-ary relations aren't helpful
in data modeling.  Nor is it an argument that you can't do semantic
integration using n-ary relations.  I simply think it's *easier* to do that
integration with the RDF approach, and I cited an historical example as
evidence that others have found that as well.  Now, they/we may have simply
missed the boat, and if so, someone (possibly you) will have to come along
and show us a better way (I'm serious).  There have certainly been attempts
to provide more general KRs (allowing n-ary predicates) for data/knowledge
exchange