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

Apparently, Frank forgot to "reply all", s I am forwarding it here.
An answer will follow.

---------- Forwarded message ----------
From: Frank Manola <fmanola@acm.org>
Date: Thu, Nov 3, 2011 at 5:20 PM
Subject: Re: relational data as a bona fide member of the SM
To: Alexandre Riazanov <alexandre.riazanov@gmail.com>


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.


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.   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.


> 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
======================================