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Re: Re: Re: Request for two new media types submitted

From: Eric Prud'hommeaux <eric@w3.org>
Date: Sat, 10 Jan 2009 19:14:55 -0500
To: Stasinos Konstantopoulos <konstant@iit.demokritos.gr>
Cc: Phil Archer <phil@philarcher.org>, Bjoern Hoehrmann <derhoermi@gmx.net>, Public POWDER <public-powderwg@w3.org>, Ivan Herman <ivan@w3.org>, Ralph Swick <swick@w3.org>
Message-ID: <20090111001454.GC14273@w3.org>
* Stasinos Konstantopoulos <konstant@iit.demokritos.gr> [2008-12-23 10:00+0200]
> On Mon Dec 22 21:26:34 2008 Eric Prud'hommeaux said:
> 
> > * Stasinos Konstantopoulos <konstant@iit.demokritos.gr> [2008-12-21 07:14+0200]
> > >
> > > On Dec 20, 2008, at 6:38 PM, Eric Prud'hommeaux wrote:
> > >
> > >> I'm not sure which of the following you are arguing:
> > >>  1 "Extends RDF" could not be interpreted as "extends the RDF data  
> > >> model"
> > >>  2 my proposed clarification is incorrect
> > >>  3 my proposed clarification is not an improvement
> > >
> > > #2
> > 
> > OK, here is the proposed wording:
> > 
> > "POWDER-S uses an <a href=
> > "http://www.w3.org/TR/2004/REC-owl-semantics-20040210/syntax.html#owl_DatatypeProperty_syntax"
> > >OWL DatatypeProperty</a> to relate a resource to a regular expression
> > which that resource matches. While POWDER-S uses OWL classes to group
> > resources, any engine determining if a resource belonged in one of
> > these OWL classes would need to be able to test a resource against a
> > regular expression."
> > 
> > What are you arguing is incorrect?
> 
> this bit here:
> 
> > "any engine determining if a resource belonged in one of these OWL
> > classes would need to be able to test a resource against a regular
> > expression."
> 
> Although that is one possible way to go about implementing a POWDER-S
> processor, it is not the only one, so it is not that case that "any
> engine ... would need".
> 
> One counter-example to the universal quantification in your wording
> is the SemPP processor (http://transonto.sourceforge.net/).
> In this approach the "engine determining if a resource belonged in one
> of these OWL classes" (which in SemPP's case is vanilla Pellet) knows
> nothing about regexps; the regexp matching is done at the RDF
> layer where nothing is known about OWL classes or any other OWL
> vocabulary.

I understand your point that the implementation seems like it is doing
matching resources against regex patterns at the core level. I argue
that the programmatic boundries don't coincide with the logical
boundries, and that the behavoir is best described as a semantic
extension. To wit, the POWDER Formal Semantics [PFS] asserts that
[[
<x, reg> is in IEXT(I(wdrs:matchesregex)) if and only if:

    * reg conforms with regular expression syntax, AND 
...
]]
all of which is in the language set aside in RDF Semantics [RS] for
semantic extensions (in fact, everything in the semext class in the
document appears to be just that, a semantic extension). It's not that
you *couldn't* define it as an extension to RDF core, it's just that
it would be painful, and the behavoir of two such extensions would not
be defined.

> > > Machinery further up the application stack (RDFS and OWL reasoners)
> > > can remain happily ignorant about what's happening underneath.
> > 
> > Ahh, I believe it is customary to treat DatatypeProperies like
> > wdrs:matchesregex or my:isEvenInteger as extensions to the inference
> > layer. 
> 
> Design choices are best made per application depending on each
> application's specific needs. POWDER extends RDF and not RDFS or OWL.

To some degree, though RDF has some text which favors one path over
another.

> > >> Equivalent, sure, but it's distracting for the reader because the
> > >> they start looking for an intersection where there is none, and.
> > >
> > > As already noted, there are good technical reasons for this  
> > > inconvenience.
> > 
> > The main reason I see for this is that the xml representation
> > expresses intersections, but not other logical constructs such as
> > unions or complements. I expect this represents the far majority of
> > use cases, as regular expressions can already express both unions
> > and if you feel like compiling them into a regex, complements.
> > 
> > Thus, all patterns can be reduced to a pure conjunction, so there's
> > less pressure for working group to include a step for simplification.
> 
> That's yet another interesting alternative for implementing POWDER-S.
> But I don't think you would prefer to have to wade through
> the single-regexp representation of a POWDER/XML <ol> element--even
> with just two branches--in the document.

Were you to be earlier in your process, I'd argue for a
post-processing XSLT with a single rule for
owl:class/owl:intersectionOf/owl:Restriction[count(/*) == 1]
to change
[[
<owl:Class>
  <owl:intersectionOf rdf:parseType="Collection">
    <owl:Restriction>
      <owl:onProperty rdf:resource="http://www.w3.org/2007/05/powder-s#matchesregex" />
      <owl:hasValue  rdf:datatype="http://www.w3.org/2001/XMLSchema-datatypes#string">(porn\.example)\/?</owl:hasValue>
    </owl:Restriction>
  </owl:intersectionOf>
</owl:Class>
]]
into
[[
<owl:Restriction>
  <owl:onProperty rdf:resource="http://www.w3.org/2007/05/powder-s#matchesregex" />
  <owl:hasValue  rdf:datatype="http://www.w3.org/2001/XMLSchema-datatypes#string">(porn\.example)\/?</owl:hasValue>
</owl:Class>
]]
but I'm content that the cost of a change like this would exceed the
benefits.

> > I was just thinking that these details could go into an issues list.
> > As editor, I found the value of the issues list was not just to
> > document outstanding issues, but to serve as a bit of a FAQ. It's
> > possible that others besides me will be struck by the complexity
> > and search for the design decision.
> 
> Please see the relevant paragraph in Section 3.1 [1], right after the
> first occurrence of a singleton intersection, and make an editorial
> comment if you feel the explanation is not sufficient.

I wasn't arguing for the spec's sake, just for ease of tracking
important controversial points.

> > > [1] http://www.w3.org/TR/2008/WD-powder-formal-20081114/#multiDRsemantics
[PFS] http://www.w3.org/TR/2008/WD-powder-formal-20081114/#SE
[RS] http://www.w3.org/TR/rdf-mt/#ExtensionalDomRang
-- 
-eric

office: +1.617.258.5741 32-G528, MIT, Cambridge, MA 02144 USA
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Received on Sunday, 11 January 2009 00:17:17 GMT

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