Dear Colleagues, (01)
A key thing to bear in mind is that you should not confuse
entity-relationship relationships (lines on a data model) with real world
relationships (situations that exist) just because they have the same name. (02)
Regards (03)
Matthew West
Information Junction
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> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-
> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Cory Casanave
> Sent: 04 November 2011 18:03
> To: edbark@xxxxxxxx; [ontolog-forum]
> Cc: Paul Brown (pbrown@xxxxxxxxx); Bauman, Bruce T
> Subject: Re: [ontolog-forum] N-RELATIONs: Formal Ontology, Semantic Web
and
> Smart Applications
>
> The other strong use-case for reification, besides n-ary, is to support
> relations as first-class elements that can also be the subject of other
> relations. I have found this essential to represent the concepts of a
domain
> accurately - "marriage" is such a relation. The other use-case for
relations
> of relations to add metadata about the assertion, including the authority
and
> time for which the relation is valid. The problem with this in RDF/OWL
> properties is that the same concept may need, at times, to be a reified
> relation but in simpler cases a single property will do. So a general
> representation seems to always need to use reification. On the down-side
> reification (in RDF/OWL) makes queries much more complex and it removed
the
> relations from any "normal" inference as they are not asserted in the same
> way.
>
> For these reasons I have concluded that the simpler approach is for all
> relations to be "first class" so that these artificial differences don't
> exist. Once that simplification is made the logic & infrastructure can
> support all relations consistently and efficiently.
>
> -Cory
>
> -----Original Message-----
> From: ontolog-forum-bounces@xxxxxxxxxxxxxxxx [mailto:ontolog-forum-
> bounces@xxxxxxxxxxxxxxxx] On Behalf Of Ed Barkmeyer
> Sent: Friday, November 04, 2011 12:32 PM
> To: [ontolog-forum]
> Subject: Re: [ontolog-forum] N-RELATIONs: Formal Ontology, Semantic Web
and
> Smart Applications
>
> The practice of reifying relations in binary models goes back at least to
> Peter Chen and the original Entity-Relationship models.
>
> That is, you make the relation itself a 'class'/'entity', and then it has
> binary relationships to each of its arguments. Each of those binary
> relationships is a term for the 'role' -- the 'argument name' if you will,
or
> in the least informative of cases, just the position number.
>
> This is precisely the recommended best practice for representing n-ary
> relationships in OWL: the relation becomes a 'class', and each of the
> argument slots becomes an objectProperty (or datatypeProperty) named for
the
> role. The domain of the argument property is the relation class and the
range
> of the argument property is the range of the argument. One can create the
> inverse of the role property where it is useful, i.e., where one needs to
> navigate the model from one argument of the relation to another.
>
>
>
> The problem the RDF folk and the OWL folk have is the absence of a way to
> declare that the 'class' term represents an n-ary relation. That is the
one
> semantic addition that is created by the UML AssociationClass.
>
> Unfortunately, the other rules for handling association classes in UML
> v1 made the structure hard to use, and many UML best practice documents
forbid
> its use. The problem for slavishly object-oriented models is whether
there is
> a difference between the role links and the attributes of the would-be
class,
> and whether a class whose instances play one of the roles has an attribute
> that refers directly to another role player, and of course, what the
resulting
> C++, C# and Java implementations will look like. An alternative used by
> database modelers in UML v2 is to create a <n-ary relation> stereotype for
> classes representing reified relations and a <role> stereotype for the
> arguments. The advantage of this approach is that it allows the modeler
to
> mark up the model to characterize participation multiplicities correctly,
and
> to create the useful inverses. And for database models, it distinguishes
the
> functional arguments (the role players and their keys) from the dependent
> variables (the other attributes and associations) in the 3rd normal form
re
> lation.
>
> All of this only says that the practice of reification of relations is
common,
> but has evolved differently for different implementation mechanisms and
for
> different semantic concerns. And make no mistake:
> Tableaux reasoning is an implementation mechanism, and more than half of
the
> RDF folk are more worried about managing triple stores than manipulating
their
> semantics.
>
> -Ed
>
> P.S. I now await John Sowa's further elaboration/correction on the
> history of reification. :-)
>
> --
> Edward J. Barkmeyer Email: edbark@xxxxxxxx
> National Institute of Standards & Technology
> Manufacturing Systems Integration Division
> 100 Bureau Drive, Stop 8263 Tel: +1 301-975-3528
> Gaithersburg, MD 20899-8263 Cel: +1 240-672-5800
>
> "The opinions expressed above do not reflect consensus of NIST,
> and have not been reviewed by any Government authority."
>
>
> David Price wrote:
> > WRT RDF doesn't it simply boil down to being based on graphs which,
> > quoting from Wikipedia, are "mathematical structures used to model
> > pairwise relations between objects from a certain collection". So, I'm
> > confused by comments like "N-ary relations work great in a graph model."
> > which seems completely at odds with the fact that graph relations are
> > pairwise.
> >
> > UML has N-ary associations and AssociationClass, so there's at least one
> > standard from which the semantics community might steal an idea or two.
> >
> > Cheers,
> > David
> >
> > On 11/4/2011 2:57 PM, AzamatAbdoullaev wrote:
> >
> >> I believe this fundamental issue more belong to the Ontolog Forum.
> >> Risk to start the n-relations thread...
> >>
> >> Azamat
> >>
> >> ----- 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>;
> >> <alexandre.riazanov@xxxxxxxxx>
> >> 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]
> >>
> >>
> >>
> >>> 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@xxxxxxxxxxxxxx>
> >>>> 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@xxxxxxx>
> >>>>>
> >>>> 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&ty
pe
> =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.
> >>>
> >>>
> >>>
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