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

On Friday, November 04, 2011 2:49 PM, Glenn 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".

That's right. 
But they have to do it because of the language restrictions. Any graph, as an ordered pair of vertices/nodes/points and edges/links/lines, is a type of binary, two-place or dyadic relation, like equality or membership. But N-relation R is a relation over the sets X1, …, Xn , which is a (n + 1)-tuple R = (X1, …, Xn, G(R)), where G(R) is a subset of the Cartesian product X1 × … × Xn where G(R) is the graph of R.
Another widespread issue with relations, instead of a meaningful intensional representation, they are mostly given an extensional interpretation, assuming that the extension of a relation is the relation itself.

Azamat
http://www.eis.com.cy
PS: 
"When two objects, qualities, classes, or attributes, viewed together by the mind, are seen under some connexion, that connexion is called a relation." A. Morgan

  ----- Original Message ----- 
  From: glenn mcdonald 
  To: AzamatAbdoullaev 
  Cc: semantic-web@w3.org ; Frank Manola ; Sampo Syreeni ; alexandre.riazanov@gmail.com 
  Sent: Friday, November 04, 2011 2:49 PM
  Subject: 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=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