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Re: Rules WG -- draft charter -- NAF

From: Jim Hendler <hendler@cs.umd.edu>
Date: Mon, 17 Nov 2003 20:38:38 -0500
Message-Id: <p05200f5bbbdf26b03155@[]>
To: Benjamin Grosof <bgrosof@mit.edu>, Sandro Hawke <sandro@w3.org>
Cc: adrianw@snet.net, www-rdf-rules@w3.org, phayes@ihmc.us
Ben - I think you miss my point - I didn't say figuring out a way to 
do NAF would be a bad thing, I said it would be a very HARD thing, 
and one for which there is no current de facto solution -- WOWG 
looked for a way to do this, and realized we would not be able to do 
it -- I don't see why the rules group would expect success unless 
they could start from an existing solution -- and I've seen no 
proposal with a solution that seems workable.  If it's going to be 
part of the charter, then I would want to see at least 1 workable 
solution before the WG starts...
p.s. WOWG's objective, which we didn't achieve, is mentioned in our 
requirements [1]

O3. Ability to state closed worlds     Due to the size and rate of 
change on the Web, the closed-world assumption (which states that 
anything that cannot be inferred is assumed to be false) is 
inappropriate. However, there are many situations where closed-world 
information would be useful. Therefore, the language must be able to 
state that a given ontology can be regarded as complete. This would 
then sanction additional inferences to be drawn from that ontology. 
The precise semantics of such a statement (and the corresponding set 
of inferences) remains to be defined, but examples might include 
assuming complete property information about individuals, assuming 
completeness of class-membership, and assuming exhaustiveness of 
subclasses.     Motivation: Shared ontologies, Inconsistency detection

[1] http://www.w3.org/TR/webont-req/#section-objectives

At 12:13 -0500 11/15/03, Benjamin Grosof wrote:
><x-flowed>Hi Jim and all,
>At 03:18 PM 11/14/2003 -0500, Jim Hendler wrote:
>>   I agree w/Sandro - NAF requires identifying a set of facts it works over
>>  (the domain) - but RDF graphs,  but their very nature are open -- so what
>>  sound easy suddenly becomes very hard.  We attcked this problem in WebOnt
>>  (see our reqs document and issues lists - sorry, I'm on slow connection
>>  don't have the URIs, but they are one link from
>>  http://www.w3.org/2001/sw/WebOnt) - we wanted a way to have a local
>>  unique names assumption - but couldn't solve the problem -- I bet the
>>  local domain naming is at least as hard, probably harder
>Would you please send me specific links when you can? I looked at the OWL
>requirements and issues list documents and I couldn't   easily figure out
>which parts of them you were referring to.
>>   here's an example, tell me whaty you would do
>>You say
>>   Rule1 - if person(shoesize) != large then A
>>   Rule2 - if person(shirtsize) != large then B
>>   RULES-CLOSED-OVER http://www.foo.bar/document1.rdf
>>and that seems fine,  but document1 includes
>>    :Joe owl:class :person.
>>    :Joe shoesize :large.
>>    :Joe nickname "the gorilla".
>>   :person rdf:type foo:human.
>>now, foo is a namespace document which contains a bunch of facts 
>>about humans.
>>It is clear that A is false, because the document you're closed over says
>>his shoesize is large
>>But what about B being true?   We see that this document doesn't include
>>that his shirtsize isn large, but what is on foo:?  Maybe it says anyone
>>with the nickname "the gorilla" where's a large shirt, maybe it refers to
>>another document, ad infinitum.
>>   So when there is a web of graphs refering to terms in other graphs, etc
>>  - how do you know where things stop?  (see www-sw-meaning for a lot more
>>  dicussion of this issue!)
>>   this is also only one simple manifestation of this problem -- when you
>>  talk about documents that are changing, scraped, etc. (all of which come
>>  up on the web) it gets even uglier
>>   Sandro put it well - it's not that we cannot do NAF, it's that designing
>>  the mechanism for definining the bounds of a graph on the web is still an
>>  unsolved problem --
>Thanks for the example, it helps.
>I think you've put your finger right on the nub of the problem.
>I was indeed presuming that there is a mechanism to define the bounds of
>the knowledge base / graph, i.e., to well-define the set of premises.
>>   if the rules group has to solve it to make progess, that is risky
>>  business....
>I think the Semantic Web needs to solve it in an initial fashion, and quite
>soon.  There's a tremendous overambitiousness in thinking that this is
>*not* critical path.  It's not so hard to do, either -- in the following
>sense.  Programming languages "solved" it long ago with mechanisms that
>check transitively for inclusion (such as the "make" facility in C).
>The obvious approach is to just use that type of idea for the Semantic
>Web.  Thus if the transitive closure of the "import" chains cannot be
>determined and meet the usual criteria of well-definedness then there is a
>KB scope violation of a "system-ish" nature.  This will force people to
>define more carefully exactly which portions of other KB's that they are
>importing -- including via more contentful module mechanisms within KB's --
>and to do integrity checking on transitive closures of inclusion both
>initially when KB's are developed and periodically/dynamically as KB's are
>   I know that some don't like the idea of having to do this.  I think the
>alternative of not being allowed to define such scoping is, however,
>extremely undesirable.  The idea of "all RDF anywhere on the web" as
>something I would want to always *have to* use as my KB's scope is a
>complete non-starter practically -- consider issues of data/knowledge
>quality alone!  (I'm tempted to say it's ridiculous.  People talk about
>"trust" on the Semantic Web.  The most basic mechanism for trust is simply
>to know what set of premises the inferences were drawn from.  We'll be
>laughed out of town in most practical IT settings if we don't have a good
>story about this aspect of things.)
>If we take the approach I'm suggesting (and others have suggested it too)
>then we don't have to get fancy about deep philosophy and unplumbed
>territory of "social meaning", or wait for more research on "trust",  to
>just get going on doing over the Web the kind of KR that has been proved in
>useful in decades of practical applications (and for a number of years in
>multi-agent systems).  We can then proceed incrementally/evolutionarily
>over time, as we develop further use cases and techniques, to open things
>up by having more implicit and relaxed mechanisms for importing / scoping
>the KB's/graphs.   We should start with what we know works, in short, and
>then work to improve upon it in the direction of reducing the burden of
>defining inclusion/import scoping.  As a practical matter, if there is a KB
>scope violation cf. above, then that doesn't mean we can't/won't do
>inferencing, depending on the purpose and kind of inferencing -- some kind
>of inferencing may be useful even when there is a violation.
>If we do it that way, we can have/do nonmon/NAF on the Semantic Web
>essentially today, and develop additional techniques later for making the
>scoping more flexible and convenient.
>>   -JH
>>p.s. Note that the OWL group rjected the solution that we could use the
>>imports closure and define everything else as not included, because that
>>would limit you to only those things defined in the DL profile, not all
>>OWL and all RDF documents
>I'm confused by this.  "All OWL and all RDF documents" is way too big --
>see above my comment about "all RDF on the Web".  When you say "DL profile"
>I presume you mean the set of OWL imports statements.  What's the point of
>an imports mechanism in OWL if everything else is included?  Perhaps I'm
>not understanding what you're saying.
>In any event, the way to go is to define (a given KB as) importing of RDF
>as well as OWL (and soon, more generally, semantic web rules knowledge base
>modules as well), in the imports profile, and stick to the transitive
>closure for most purposes.  Does that require extending the current imports
>mechanism of OWL, e.g., to define a boundaried RDF graph as imported?
>>-- the rules language would have to face that same issue, but also deal
>>with all things findable by Xquery ... yow!
>I don't see what XQuery has to do with it (at least not directly), if we're
>talking RDF stuff.  XQuery is certainly related to Semantic Web Rules
>(indeed, I was one of the first to press this point to the W3C team; back
>in March 2001 I presented to them about it), but I don't see that Rules
>"have to... deal with all things findable by XQuery".  More pertinent to
>the main topic here is that XQuery deals quite ambitiously with very large
>scale databases and as I understand it (from early versions I looked at)
>has a well-defined boundary of what is queried over.  That's thus probably
>further evidence towards the usefulness of my scoping suggestion about
>imports closure.
>>Professor James Hendler                   http://www.cs.umd.edu/users/hendler
>>Director, Semantic Web and Agent Technologies     301-405-2696
>>Maryland Information and Network Dynamics Lab.    301-405-6707 (Fax)
>>Univ of Maryland, College Park, MD 20742          240-277-3388 (Cell)
>Prof. Benjamin Grosof
>Web Technologies for E-Commerce, Business Policies, E-Contracting, Rules,
>XML, Agents, Semantic Web Services
>MIT Sloan School of Management, Information Technology group
>http://ebusiness.mit.edu/bgrosof or http://www.mit.edu/~bgrosof

Professor James Hendler			  http://www.cs.umd.edu/users/hendler 
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-277-3388 (Cell)
Received on Monday, 17 November 2003 20:40:20 UTC

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