Re: example of asn07 as OWL subset, musings on RDF/XML

Sandro Hawke wrote:
> Perhaps it sheds a little light on the RDF/XML syntax debate to show the
> OWL version of the asn07.  The idea here is that we're modeling an
> idealized rule system, or, equivalently, we're modeling the information
> transmitted in RIF.
> 
> This OWL-DL ontology was generated from a random strawman abstract
> grammar for BLD.   (I took the asn from BLD some time ago and modified
> it in random ways, playing around.)
> 
> The asn07:
>    http://www.w3.org/2007/08/rif-absyn/foo.asn
> The equivalent OWL:
>    http://www.w3.org/2007/08/rif-absyn/foo.owl
> 
> Now, it's not quite equivalent.  In particular, the OWL version does not
> constrain the syntax of lists, because you're not allowed to talk about
> RDF lists in OWL-DL.   I'm not sure whether to address this with using
> non-RDF lists, use OWL-Full for this part, or use some other formalism
> (eg BLD :-).
> 
> I've looked at this ontology in Protege4 and Pellet and it seems to say
> the right things.   I can think of tests I haven't done.
> 
> The point here is that a RIF document / ruleset can be nicely talked
> about using objects (or, essentially, using relational data or RDF).  
> 
> So, I think it's clear that a RIF document *can* be transmitted in
> RDF/XML.  The data model of the syntax is compatible with the RDF data
> model (which isn't surprising, since at this level of details it's a
> generic object model).  And if we make a non-RDF/XML syntax, we can
> define a GRDDL transform to RDF/XML, so the semantic issues the same.

Well, not quite. I mean, any XMl can be transformed to RDF by the GRDDL 
detour, but I'd not expect GRDDL transforms are to be dealt with 
natively (at the semantic level) in RIF), whereas we seem to intend to 
do so with RDF. I just wondered what RIF/RDF *means* in RIF if RDF 
itself has a meaning in RIF by the discussed embedding/model theory 
combination...

If we say that RIF documents have a meaning in terms of RDF and RDF 
graphs have a meaning in terms of RDF vice versa, then I am somewhat 
afraid that we  run IMO into something strange (which was what I was 
trying to ask at the end of the phone conf today...)

1) Take an RDF graph

s p o .

2) In RIF this means:

Forall s[p->o].

3) This is in "RIF/RDF" something like (I assume here the RDF reading of 
the RDF/XML):

_:f a Forall.
_:f rif:formula _:f1.
_:f1 a Frame.
_:f1 rif:oid s.
s a rif:Const.
_:f1 rif:slot _:s.
_:s rif:slotTerm p.
p a rif:Const.
_:s rif:slotValue o.
o a rif:Const.

(I had to invent new properties here for the slotTerm  and slotValue, 
BTW, because I wouldn't know how to otherwise tweak the term-value pair 
into RDF)

4) Now, this in turn again is to be interpreted in RIF as:

Forall Exist _:f _:f1 _:s
  AND( _:r[rdf:type -> rif:Ruleset].
       _:r[rif:formula -> _:f].
       ...
     )

BTW: the blank nodes as existentials is probably not right here, since 
it is in the head, I should have skolemized, therefore

Forall
  AND( sk:r[rdf:type -> rif:Ruleset].
       sk:r[rif:formula -> sk:f].
       ...
     )

5) Now this in turn in RIF/RDF "means"

_:f a Forall.
_:f rif:formula _:f1.
_:f1 a Frame.


6) proceed analogous as in 4) ... running into kind of an endless blowup 
of reifications, if you want.

This can be played on until infinity... I think, if we want something 
RDF "readable" we should then have something "hybrid" which leaves
RDF data as RDF data, if possible, and only adds RDF annotations for 
rules as necessary (which could be implicit, sure).

I am not sure at the moment, how such a hybrid syntax could look like, 
but would ... rather than the above, envision some minimal requirements 
I would like in a RIF/RDF syntax:
=====================================================================
1) s p o. (in RDF) =  s p o. (in RIF/RDF)
  ie. no difference for pure data/or facts.

2) I would't bloat up slots (occurring in rule heads or bodies) to 
anything more than triple(-patterns) with possibly variables.

3) It should be guaranteed that the RDF version of a ruleset r 
(RDF-)merged with some RDF graph g should not possibly change the 
RIF-meaning of the *single rules* in r. ie, it should be allowed to 
merge rulesets, rulesets and data, but not data into rules by simply 
merging the representing RDF graphs.
=====================================================================

I am not 100% sure about 2), but interestingly, 2) in my view rather 
cries for viewing RIF syntax rather as an *extension* of RDF(syntax) 
than an embedding RIF itself *into* RDF syntax... (just like XML is 
embeddable in RDF in the form of XML literal values). LEet me give an 
example of another spec which follow similar thoughts, it seems:

SPARQL: Remarkably, SPARQL's syntax *does* build upon a very successful
(because easily human as well as machine readable) syntax: Turtle.
I don't see any intention in SPARQL to define an RDF syntax for SPARQL 
itself. Even thinking about an XML syntax for SPARQL was postponed so 
far. Also, the result format (except for CONSTRUCT queries) is XML - and 
not RDF. All that for a language which is to be a core Semantic Web 
language!

This is not meant as opposing a RIF/RDF syntax per se, and the SPARQL 
analogy merely came to my mind because I was doing some research about 
SPARQL (and the possible usage of SPARQL itself as a rules language) 
recently [2].
  Anyway, this is meant to start a deeper discussion about what an 
RIF/RDF syntax shall achieve and why do we want/need it and what are the 
implications. You might well completely disagree with my minimal 
requirements outlined above...

best regards,
Axel

[2] Axel Polleres, François Scharffe, and Roman Schindlauer. SPARQL++ 
for mapping between RDF vocabularies. In Proceedings of the 6th 
International Conference on Ontologies, DataBases, and Applications of 
Semantics (ODBASE 2007), Vilamoura, Algarve, Portugal, November 2007. To 
appear. http://www.polleres.net/publications/poll-etal-2007.pdf


1. Axel Polleres, François Scharffe, and Roman Schindlauer. SPARQL++ for 
mapping between RDF vocabularies. In Proceedings of the 6th 
International Conference on Ontologies, DataBases, and Applications of 
Semantics (ODBASE 2007), Vilamoura, Algarve, Portugal, November 2007. To 
appear. http://www.polleres.net/publications/poll-etal-2007.pdf

> The question is just whether the *primary* *normative* syntax is a
> subset of RDF/XML or is some other essentially-equivalent XML syntax.
> 
>>From my perspective, it seems easier to just talk about transforms on
> the semantic-level data -- that is, the object model -- not on the XML
> form.
> 
>      -- Sandro
> 
> 


-- 
Dr. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/

Received on Tuesday, 18 September 2007 22:00:46 UTC