Standard representations for n-ary relations [was: Re: relational data as a bona fide member of the SM]

Plus RDF doesn't have any *standard* way to tag or represent n-ary
relations -- we have taken a do-it-yourself attitude[1] -- and thus
tools cannot predictably recognize n-ary relations as such.  

Personally, I think this is something that would be good to address, and
there are several simple ways it could be done.

1. http://www.w3.org/TR/swbp-n-aryRelations/

David

On Fri, 2011-11-04 at 08:49 -0400, glenn mcdonald wrote:
> 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=pdf by 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

-- 
David Booth, Ph.D.
http://dbooth.org/

Opinions expressed herein are those of the author and do not necessarily
reflect those of his employer.

Received on Friday, 4 November 2011 13:20:16 UTC