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

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=pdfby 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.


> A related thing I hate about RDF (as a practitioner) is the poor data
> model. In particular, the open world assumption does not allow to fully and
> unambiguously describe some objects. Pragmatically, it would be nice to
> have something like the ML data model.
>
>
> This isn't a pragmatic vs. theoretical issue, it's a question of what
> problem you're trying to solve.  RDF is based on the open world assumption
> because it's designed with the Web in mind, and the Web, unlike a
> relational database, is open.
>

I don't have a problem with the OWA in general. The problem is the OWA is
there even when you
don't want it, specifically when you want to be able to specify a piece of
data completely and unambiguously. With OWA, you cannot compute the length
of a list because somebody else can redefine the list somewhere.


>   A pragmatic approach to dealing with Web data needs to take that into
> account.  On the other hand, if you want to consider some collection of RDF
> as being closed, I don't know anything that would stop you from doing that
> (e.g., stick it in a relational database and use SQL on it).
>
>
>
> On Thu, Nov 3, 2011 at 4:57 AM, Sampo Syreeni <decoy@iki.fi> wrote:
>
>> As a relational minded guy, I wonder why there aren't any genuinely
>> relational minded formats/syntaxes/data around, which still embody the
>> SemWeb/LinkedData mindset. I mean, that ought to be pretty easy to do, and
>> it then ought to bring all of the benefits which once made RM so great and
>> overpowering.
>>
>
> Well, why don't you guys have a go at it?   This would be a forum where
> you could bounce some ideas around.
>
>
Hmm.. I apologise if this list is not an appropriate place.


>
>> Why precisely do all of the semweb formats stay ternary, thereby forcing
>> themselves to reify any higher arity, and as such complicate the processing
>> of higher arity data by adding an extra reification layer?
>> --
>> Sampo Syreeni, aka decoy - decoy@iki.fi, http://decoy.iki.fi/front
>> +358-50-5756111, 025E D175 ABE5 027C 9494 EEB0 E090 8BA9 0509 85C2
>>
>>
>
>
> --
> ======================================
> Alexandre Riazanov (Alexander Ryazanov), PhD
> Saint John, New Brunswick, Canada
> Skype: alexandre.riazanov
> http://www.freewebs.com/riazanov/
> http://www.linkedin.com/in/riazanov
> http://www.unbsj.ca/sase/csas/faculty.php
> ======================================
>
>
>


-- 
======================================
Alexandre Riazanov (Alexander Ryazanov), PhD
Saint John, New Brunswick, Canada
Skype: alexandre.riazanov
http://www.freewebs.com/riazanov/
http://www.linkedin.com/in/riazanov
http://www.unbsj.ca/sase/csas/faculty.php
======================================