- From: Jim Hendler <hendler@cs.umd.edu>
- Date: Wed, 22 Jun 2005 12:55:08 -0400
- To: Jos de Bruijn <jos.debruijn@deri.org>, dreer@fh-furtwangen.de
- Cc: public-sws-ig@w3.org
- Message-Id: <p06200775bedf4532d2b2@[172.31.0.192]>
Jos-
that's not quite right as I understand it - to use an example from
the paper I cited -
Given an ontology containing only a single RDF triple:
<#pat> <#knows> <#jo>.
the answer to a query asking if pat knows exactly one person would be
"no" under
RDF's open world semantics, but "yes" under the closed world
semantics of Datalog.
there's no negation explicit here.
btw, this is not a small issue to me -- without some way to control
default reasoning (i.e. limit the scope of axioms and facts that are
considered for a set of queries) there is just no way to link things
reliably on the Web (and without the linking, why bother with Web).
As far as I'm concerned, the minute one assumes there is a
mechanism to close a graph (and several are floating around), then
ontology and rules go together just fine and lots of the layering is
fixed. On the other hand, if a rule can be stated in general that
has a negation as failure then we have a problem.
In the old days, for example my thesis work, we used "ThNOT" in
langauges like MicroPlanner, NASL, etc. and that was some of the
earliest work on this stuff. The idea was you could use a rule like
this
P :- ThNOT Q.
to mean P is true if you cannot prove Q. Implicit in this, and many
of the systems since, was the idea that there existed "A knowledge
base" which was all the facts that this rule could be used on.
On the Web, I would want this to read something like
P :- (Thnot Q) given R.
where "given R" somehow means with respect to some database, some
graph, or some other nameable and definable entity.
Thus, for example, one could imagine running a query against some
graph (and note in theory that this could be the identity query,
meaning it is equal to everything in the graph) and then stating that
some set of rules is applied with respect to the resulting graph.
These rules having NAF would be great and good and wonderful. If I
applied your rules to a different graph, it would be up to me to
decide if I wanted to restrict things in my graph to control the
scope of the application of your rules -- this sounds like a powerful
and crucial mechanism, and with it a lot could be done. Without it,
rules on the web seem to me to either be just doing logic programming
with a consistent syntax (in which case why invent all these
languages, let's just use Prolog on the Web) or pretending the whole
Web can be treated like a closed world - and that's, in my mind,
where the dragons are...
JH
At 10:46 -0400 6/22/05, Jim Hendler wrote:
>At 12:04 +0200 6/22/05, Jos de Bruijn wrote:
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>>Dreer Michael WI wrote:
>>
>>>Hello,
>>>
>>>what is the relationship between WRL and SWRL?
>>
>>Hello Michael, others,
>>
>>With WRL we take an approach different from SWRL. We build on the
>>experience in
>>the Logic Programming and Deductive Database communities (and
>>partially other rules communities) and (syntactically) restrict
>>ourselves to Horn and add nonmonotonic negation, whereas SWRL stays
>>within a First-order framework and simply extends the expressiveness
>>of OWL DL. WRL extends a subset of OWL DL; this subset which falls in
>>the framework of standard Horn rules.
>>
>>
>
>Sorry, but this cannot be right. SWRL assumes closed world
>semantics and WRL assumes open world semantics. Thus, we get
>completely different entailments in an OWL/RDF world than in a WRL
>one, so we are talking something very different than a subset
>relationship. Ian Horrocks, Peter Patel-Schneider, and Bijan Parsia
>(with me as a kibbitzer) wrote a short paper about this available at
>[1]
>
>Let me be clear, I'm all for Web (and Sem Web) rules languages, but
>if it isn't open-world, I don't see how it can be Sem Web, since it
>violates the base assumption on which all of RDF, RDFS, and OWL sit.
>This is easily fixable, and at the Rules workshop the idea of a
>"Scoped Negation as Failure" was developed to handle this -- I'd
>love to see WRL (and SWRL) extended to have a SNAF mechanism,
>because then we don't violate the basic principles of the Web
>architecture and the Semantic Web, but we should be precise - two
>things with very different Semantics and entailments cannot be
>referred to as subsets of each other.
>
> -JH
>
>
>
>
>[1] http://www.cs.man.ac.uk/~horrocks/Publications/download/2005/HPPH05.pdf
>
>>Best, Jos
>>
>>>
>>>Thanks in advance
>>>
>>>Michael Dreer
>>>
>>>
>>
>>> Steve Ross-Talbot wrote:
>>>
>>> >>Out of curiosity and also business pragmatics what is the relationship
>>> >>between WRL and RuleML?
>>>
>>>
>>>
>>> RuleML provides an extensive lattice of sublanguages ranging from
>>> production rules to regular LP rules to First-Order Logic, es well as
>>> sublanguages with such features as slotted syntax, meta-programming, and
>>> courteous logic programming.
>>>
>>> WRL makes a choice to use include particular features in the language.
>>> It turns out that these features correspond to certain RuleML
>>> sublanguages to a great extent. Therefore, RuleML can be used for the
>>> XML serialization of a large part of the language.
>>>
>>> The following document describes the (RuleML and other) schemas used for
>>> the XML serialization of WRL:
>>>
>>> http://www.wsmo.org/wsml/wrl/wrl-xmlschemas.html
>>>
>>> More details on the XML serialization of WRL can be found at:
>>>
>>> http://www.wsmo.org/wsml/wrl/wrl.html#cha:wrl-xml
>>>
>>> I hope this clarifies the issue.
>>>
>>>
>>> Best, Jos
>>>
>>>
>>> >>Cheers
>>> >>
>>> >>Steve T
>>> >>
>>> >>On 21 Jun 2005, at 08:28, Jos de Bruijn wrote:
>>> >>
>>> >>Dear all,
>>> >>
>>> >>On behalf of WSML, AIFB and NRCC I am pleased to announce:
>>> >>
>>> >>The Web Rule Language WRL - version 1.0:
>>> >>
>>> >>http://www.wsmo.org/wsml/wrl/
>>> >>
>>> >>
>>> >>WRL is a rule language for the Web and the Semantic Web and was
>>> >>heavily influenced by the Web Service Modeling Language WSML
>>> >>(http://www.wsmo.org/wsml/wsml-syntax).
>>> >>
>>> >>
>>> >>Best regards,
>>> >>
>>> >>Jos de Bruijn
>>> >>
>>> >>>>
>>> >>>>
>>>
>>>
>>> --
>>> Jos de Bruijn, http://www.uibk.ac.at/~c703239/
>>> +43 512 507 6475 jos.debruijn@deri.org
>>>
>>> DERI http://www.deri.org/
>>> ----------------------------------------------
>>>
>>> Only two things are infinite, the universe and
>>> human stupidity, and I'm not sure about the
>>> former.
>>> -- Albert Einstein
>>
>>
>>- --
>>Jos de Bruijn, http://www.uibk.ac.at/~c703239/
>>+43 512 507 6475 jos.debruijn@deri.org
>>
>>DERI http://www.deri.org/
>>- ----------------------------------------------
>>
>>Only two things are infinite, the universe and
>>human stupidity, and I'm not sure about the
>>former.
>> -- Albert Einstein
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>
>--
>Professor James Hendler Director
>Joint Institute for Knowledge Discovery 301-405-2696
>UMIACS, Univ of Maryland 301-314-9734 (Fax)
>College Park, MD 20742 http://www.cs.umd.edu/users/hendler
--
Professor James Hendler Director
Joint Institute for Knowledge Discovery 301-405-2696
UMIACS, Univ of Maryland 301-314-9734 (Fax)
College Park, MD 20742 http://www.cs.umd.edu/users/hendler
Received on Wednesday, 22 June 2005 16:55:45 UTC