I share Ed's concerns. Just want to add that most programming questions come
from the ontology of relations, which is still in need to specify the
following crucial issues:
1. the reality relationship, its ontological status, if it's a real entity
or just attributions.
2. ontological priority of objects and relations, if
substances/objects/classes are just agglomerations of relationships.
3. kinds and sorts of relationships.
4. hierarchy of relations: as causal, natural, conceptual, logical, etc.
5. symbolic, formal representations of relationships.
The supertask is to establish a common theory of entities and relationships,
as the framework for relationships representation and reasoning.
Azamat
----- Original Message -----
From: "Ed Barkmeyer" <edbark@xxxxxxxx>
To: "[ontolog-forum]" <ontolog-forum@xxxxxxxxxxxxxxxx>
Sent: Friday, November 04, 2011 6:31 PM
Subject: Re: [ontolog-forum] N-RELATIONs: Formal Ontology, Semantic Web and
Smart Applications (01)
> 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 relation.
>
> 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&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.
>>>>
>>>>
>>>>
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