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Re: Comments on * DRAFT * Rules Working Group Charter $Revision: 1.60 $

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Tue, 23 Aug 2005 00:59:45 -0400
To: Jim Hendler <hendler@cs.umd.edu>
Cc: public-rule-workshop-discuss@w3.org
Message-Id: <20050823045945.6B4A1CB5D3@kiferserv.kiferhome.com>

Jim Hendler wrote:
> Dieter,
> I think there is a lot of confusion her .  Let me address three points
> 1 - what the intent of the WG being defined should (IMHO) be
> 2 - the relationship with OWL which I think you mistakenly undervalue
> 3 - the issue of NAF (and SNAF) which is so important to this stuff 
> working on the Web
> I think the real problem Sandro and the W3C have been facing is NOT 
> about OWL (I return to this later) but primarily about whether we are 
> looking at a Rules language envisioned as a language for USING rules 
> on the Web, or a Rules language envisioned as a language for 
> EXCHANGING rules on the Web.  As Sandro got more feedback from 
> industry (some of it on this list), it is clear that there was more 
> of a need for the latter among the business rules community than for 
> the former.  Where most of us in research (thee and me included) have 
> been focused on rule as reasoning, we have been less focused on the 
> exchange of rules.   The former wants a language which is 
> computationally efficient and usable, the latter needs a very 
> expressive language. 


An exchange language is about XML syntax. You don't need semantics for
that---only an encoding. This is not what the proposed draft appears to be
suggesting.  If an exchange syntax was all that they wanted (and not a
language for USING rules) then the drafters of that charter are confused,

> In fact, the business rules community has 
> rejected most of the LP approaches used in reasoning in the past (and 
> papers at this workshop said so in no uncertain terms) because their 
> needs were not addressed by what we were producing.

Would you care to back the above sweeping statement with concrete facts?

I assume that you are not talking about the good old 80's when -- out of
ignorance and incompetence -- some in the industry tried to use LP for
every possible computing task.

> The current 
> charter claims FOL is the right choice for this more expressive 
> language - something which you question (and I do too, although not 
> because of the same reasons you state).  So one way to think of this 
> WG is as a "RULES EXCHANGE" WG and the stuff we do and care about 
> would be to define a subset of the language that is computationally 
> efficient (much as OWL-DL is a subset of OWL that is computationally 
> better - OWL Full is the real ontology exchange language, OWL-DL is a 
> subset for certain kinds of reasoners that need computational bounds).

Are you still talking about a language for EXCHANGING rules?
You lost me here.

> 2 - Relationship with OWL


I took the liberty to snip this long paragraph because, I think, you are
arguing in vain. Nobody disagrees with that. You just made a wrong
assumption that an LP rules language implies that OWL ontologies must be
rewritten using rules. This is not what anybody of us has in mind.

(We are sensible people, if I need to state that :-)

I believe that you misunderstood Dieter's comments about OWL. They were
about the requirements for going forward and why OWL is not the right basis
for that in certain cases. (Remember the 2 vs. 1 stack debate?)

> 3 - Addressing NAF
> Here's the thing I cannot understand in what you propose - NAF 
> requires a closed world to reason with respect to (that is we must 
> say "if X is not true in Y, then Z" - there must be a Y there).  The 
> Web clearly cannot be considered such a closed world (even if it 
> could, its current size is such that nothing invented to date could 
> possibly contain all the information in it - even for the current 
> semantic web this is foolish to consider).   What is easily imagined 
> is that a mechanism can be derived that expresses what particular 
> world some rule base is closed with respect to.  For example, if I 
> use SPARQL to query some triple store (which itself may be thought of 
> as an open world since it is linked to other stores and changes over 
> time etc.) for the response to some query , then that response can be 
> made into a graph that I can consider closed (and which I can name - 
> since the date/time of the query could be appended, or other such 
> mechanism).  SImilarly, if I apply the rules to some database, that 
> database could be named.  This was called SNAF at the workshop (and 
> has a number of other names in the research community, but we'll go 
> with SNAF for now).
> In principle, this puts almost no constraints on the use of the Web 
> Rules language - I can imagine a lot of designs in which a header is 
> used to designate the type of entity the rules are expected to be 
> applied to (database, RDF graph, web document, etc.) and then the 
> rules could be expressed using a NAF mechanism with respect to that 
> -- this means I would know seeing a rule set intended for some 
> particular application what it was meant to be applied to.  These 
> things could be very specific (here is my set of rules with respect 
> to some particular website) or very general (this set of rules is 
> assumed to work for any RDF graph).  As best I can tell, cases like 
> this last one would be virtually indistinguishable from NAF in 
> practice, but would be critically different with respect to the Web, 
> since developers' intent as to what the closed world is expected to 
> be could be encoded.
> There's nothing pejorative with respect to rules in thinking that 
> the Web should not be considered a closed world - just seems like an 
> obvious thing to do given the size and dynamicity of the Web.
> (btw, I think the discussion of NAF/SNAF in the proposed charter 
> needs work, and that ruling NAF out of scope makes it sound like 
> limited versions would be disallowed - which I agree with you would 
> likely be a mistake.)

NAF is a special case of SNAF.  Again, the drafters of the charter were
seriously confused when they said that SNAF is "in" and NAF is "out."

>From what you wrote above, I also get the impression that by SNAF you mean
scoped application of CWA only at the level of plain database facts. SNAF
is a more general concept than that (and a more important one).

> So - if you look carefully, I'm agreeing with most of your main 
> points, but recasting them somewhat
> i. The rules language you have been promoting seems to me should be 
> a subset of the more general rules exchange one.  I'm open to that 
> happening within the WG (the way OWL DL was created within the OWL 
> Full language) or not depending on the members and the chair and 
> their desires.  If the WG doesn't do it, I would fully expect to see 
> several member submissions, and maybe a de facto standard, by the 
> time the WG was at CR (and maybe the WG would consider making the 
> existence of such a CR exit criterion).

Again, EXCHANGE means XML syntax to me.  Then you need to decide WHAT
concrete languages you are going to exchange. FOL is NOT a more general
language -- it is a different language, and it is not a rules language. You
may need to exchange FOL as well as other rule sets. The way this is
phrased in the draft charter is a result of a serious confusion, IMO
(pardon for repeating this the second time).

If we are talking about exchange, then we already have RuleML. It provides
exchange syntax for a variety of languages. Tweaking it hear and there will
to the exchange trick.

> ii. Your gratuitous OWL bashing aside, it is pretty clear to anyone 
> who is talking to large companies that there need to be both OWL-like 
> vocabulary definitions and rule-like "data handlers" that coexist to 
> the maximum extent possible.  Different parts of the organization are 
> likely to be developing the two - and the more incompatible they are, 
> the more the situation looks like the problem we're trying to solve - 
> lack of interoperability among different parts of the information 
> space.  The proposed charter leaves a lot of space for this to happen 
> - again, this may be within the WG or without - but I do think the WG 
> is responsible for defining it precisely based on the W3C process 
> rules which  essentially require newer languages to explain 
> compatibility (or not) with earlier languages - with a high bar to 
> incompatibility
> iii. The distinction between NAF and SNAF is not nearly as 
> complicated as people seem to think conceptually (the devil is, of 
> course, in the details).  In both cases the intent is to allow a form 
> of closed world reasoning in the open world of the web.  Rules for 
> the Web cannot possibly be identical to non-Web rules or we wouldn't 
> need anything new -- much as the Web is to traditional hypertext 
> systems, or OWL is to traditional AI KR languages, the Web rules 
> language will need to extend what has been done in the past in 
> (preferably) small and subtle ways to make it work with the Web.  I 
> think SNAF v. NAF is one of those pieces of magic that will help make 
> this work.
> Hope all this helps

No, it doesn't help.

This SNAF v NAF, as I said, is a result of a serious
confusion (apologies for repeating this for the third time).  NAF is
just a special case of SNAF. All this "vs" and "distinction" in the paragraph
above only serves to propagate the confusion.

Received on Tuesday, 23 August 2005 05:01:21 UTC

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