FWIW - I never finished the paper I was working on about n-ary
relationships. Too much tactical work got in the way. Might be a good
time to revisit. Is the W3C paper below considered authoritative? (01)
On 11/4/11 7:57 AM, "AzamatAbdoullaev" <abdoul@xxxxxxxxxxxxxx> wrote: (03)
>I believe this fundamental issue more belong to the Ontolog Forum.
>Risk to start the n-relations thread...
>----- 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:
>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 -- 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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