I believe this fundamental issue more belong to the Ontolog Forum.
Risk to start the n-relations thread... (01)
----- Original Message -----
From: "David Booth" <david@xxxxxxxxxx>
To: "glenn mcdonald" <glenn@xxxxxxxxx>
Cc: "AzamatAbdoullaev" <abdoul@xxxxxxxxxxxxxx>; <semantic-web@xxxxxx>;
"Frank Manola" <fmanola@xxxxxxx>; "Sampo Syreeni" <decoy@xxxxxx>;
Sent: Friday, November 04, 2011 3:13 PM
Subject: Standard representations for n-ary relations [was: Re: relational
data as a bona fide member of the SM] (03)
> Plus RDF doesn't have any *standard* way to tag or represent n-ary
> relations -- we have taken a do-it-yourself attitude -- 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/
> 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.
>> On Friday, November 4, 2011, AzamatAbdoullaev <abdoul@xxxxxxxxxxxxxx>
>> > 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":
>> > 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@xxxxxxx>
>> > 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
>> 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
>> > 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.
> Opinions expressed herein are those of the author and do not necessarily
> reflect those of his employer.
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