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

From: <jos.deroo@agfa.com>
Date: Sat, 20 Aug 2005 14:08:21 +0200
To: adrianw@snet.net
Cc: Dieter Fensel <dieter.fensel@deri.org>, public-rule-workshop-discuss@w3.org, public-rule-workshop-discuss-request@w3.org
Message-ID: <OF3CFE736A.58935250-ONC1257063.0042A4AA-C1257063.0042A886@agfa.com>

Adrian, it is at http://www.w3.org/2005/07/rules/charter

Jos De Roo, AGFA http://www.agfa.com/w3c/jdroo/

Adrian Walker <adrianw@snet.net>
Sent by: public-rule-workshop-discuss-request@w3.org
20/08/2005 14:05

        To:     Dieter Fensel <dieter.fensel@deri.org>
        cc:     public-rule-workshop-discuss@w3.org, (bcc: Jos 
        Subject:        Re: Comments on * DRAFT * Rules Working Group Charter   $Revision:   1.60 

Dieter, All --

Where on the Web is the current draft please?  The only one Google can 
is [1] from 2003 !

Thanks in advance for a URL.


[1]  http://www.w3.org/2003/10/swre578

Online at www.reengineeringllc.com

Adrian Walker
Reengineering LLC
PO Box 1412
CT 06011-1412 USA

Phone: USA 860 583 9677
Cell:    USA  860 830 2085
Fax:    USA  860 314 1029

At 06:10 PM 8/19/2005 +0200, you wrote:

>Comments on * DRAFT * Rules Working Group Charter $Revision: 1.60 $
>First, the draft does not at all reflect the majority of the discussions 
>during the W3C workshop on rule languages that had the aim to lay the 
>ground. In the future, we can save traveling overhead if these workshops 
>and their discussions are largely ignored anyway based on predefined 
>opinions. What is sketched as a charter draft reflects the opinion of a 
>small (but noisy) minority at this workshop. In general, I would like to 
>raise the following four issues.
>1) Can OWL really provide a lot of support for use cases asking for 
>The agenda mentions "that some use cases for rules can be addressed with 
>OWL". Indeed, it was funny (or frankly spoken, painful) to see during the 

>workshop that people used range and value restrictions in OWL as 
>constrains excluding certain values for attributes. Fortunately, nobody 
>had told them that OWL would simply ignore these "constraints" and infer 
>artificial equalities of instances instead.
>2) A rule language should be based on full first order logic with 
>We will first explain why and then why not.
>2.1 Why
>We simply do not know.
>2.1.a Why full first order logic?
>No justification is given in the text! The reader can only guess that the 

>reason is to define the rule language as an extension of OWL.
>2.1.b Why equality?
>No justification is given in the text! The reader can only guess that the 

>reason is to define the rule language as an extension of OWL.
>2.2 Why NOT
>We have good reasons to believe that it is not a good choice to define a 
>rule language as a first-order language with equality.
>2.2.a Why NOT full first order logic
>Without any justification the charter requires that the rule language is 
>based on full first order logic. Notice that none of the existing rule 
>languages and their implementations are based on such a paradigm. 30 
>of research and industrial practice are ignored WITHOUT ANY 
>The draft charter becomes a parody when it states: "It is understood that 

>not all rule engines will offer complete FOL reasoning." This is a funny 
>understatement! There will never be any inference engine in our universe 
>that will offer complete FOL reasoning. This is precisely one of the 
>reasons for 30 years of research on syntactical sub languages of FOL and 
>the usage of minimal model semantics. The proposal would destroy all 
>useful computational properties of rule languages for the sake of 
>it as an extension of OWL. (a) All problematic design decisions of OWL 
>would be inherited by the rule languages (For example, rules could have 
>been layered on top of OWL Lite, if this language would have been defined 

>more appropriate and minimalistc). (b) Instead of nice computational rule 

>languages, a first order zombie language is generated that has neither 
>complete and correct, nor efficient reasoning support. This applies to 
>practical as well as theoretical aspects.
>Not only is any justification missing why the rule language should be 
>based on full first order logic with equality. Moreover, this decision is 

>used to ignore significant requirements of industry working with 
>rules.  "...Negation as failure ... (is) out of scope."
>Why? Because "combining it with FOL (is) an unsolved research problem." 
>And this in  the case where "NAF is essentially the type of negation seen 

>in many commercial and research rule systems". Why can industry and many 
>research prototypes deal with NAF when the working group can not? The 
>reason is that the working group uses without any justification first 
>order logic with equality and "combining it with FOL is an unsolved 
>research problem." Because of this, most research on rule based systems 
>and important requirements of industry are ignored. Similarly, update 
>operations and evaluation strategies of rule based systems are ignored 
>when they do not fit into the unjustified theoretical framework. If you 
>only have a hammer everything has to be a nail! Why not simply getting 
>of a non-justified and wrong choice for the underlying logical model 
>instead of ignoring most research on rules and all important requirements 

>of industry?
>2.2.b Why NOT equality
>Firstly, many equalities in the context of the web (like addresses in a 
>Unix file system used as URIs) are very cumbersome to model in logic. An 
>oracle, external to a logical language (that provides a unique identifier 

>for equivalence classes of terms), seems to be a much more useful tool. 
>Secondly, equality significantly blows up the reasoning costs of a 
>language when simple syntactical term matching to decide whether two 
>identifiers are equal is replaced by costly logical inference over axioms 

>and all their many ***many*** consequences on whether the two terms have 
>to be viewed to be equal. In a nutshell: it costs a lot and it is of very 

>limited use. Why would you want to buy into it?
>3 OWL and a rule language
>It is a well-know result from theoretical and practical work around first 

>order logic that the language is undecidable in general and difficult to 
>evaluate in computational terms. Therefore, a lot of research has been 
>done during the last fifty years to come up with more narrowly defined 
>logical languages. One example is the Description Logic paradigm that 
>underlies OWL and a second example is Horn logic with minimal model 
>semantics that underlies most implementations of rule based systems. 
>Unfortunately, it is also a well-known fact that it is not possible to 
>straight-forwardly combine both language paradigms without destroying the 

>interesting and useful computational properties of both. Therefore, 
>integration can only be done at a minimal level ensuring that none of the 

>both language types are destroyed in their justification.
>SWRL and SWRL-FOL, which are mentioned as positive examples in the draft 
>agenda, do precisely the opposite. They naively extend Description Logic 
>with a rule syntax. Therefore, they end up in an undecidable language, 
>same way first order logic is. That is, these languages restrict the 
>expressive power and enforce cumbersome syntax of FOL without providing 
>anything in return in terms of reduced computational complexity. This 
>happens when you ignore 30 years of research. These languages are neither 

>justified by a proven body of research nor by a body of implemented 
>reasoners nor industrial experience. It is quite hard to understand why 
>W3C wants to commit to such enterprises?
>The precise definition of what could be a maximal intersection of rules 
>and description logic being minimalistic enough for not destroying the 
>computational properties of the resulting language is currently the 
>battleground for many PhD students and at the same time an interesting 
>topic of research for the next years. But it is not at all the task of 
>to standardize very early drafts of PhD theses. And for sure, this 
>intersection will be less expressive than the ones mentioned in the draft 

>4) Summary
>In general, there is a high risk that a working group with such an agenda 

>generates serious damage to
>- the semantic web by providing a useless language with unmanageable 
>computational properties;
>- the rule industry since important features are simply ignored by this 
>proposal and a language that has nothing to do with the rule paradigm is 
>offered as exchange format;
>- the general reputation of W3C as a place where consensus is achieved 
>without manipulation; and
>- the general reputation of W3C as a producer of recommendations of high 
>Given the current draft, we would rather prefer not seeing a working 
>or renaming the working group to "A working group on extensions of OWL 
>towards a not well-justified sub fragment of first order logic with 
>equality." However, with OWL-Full we already have a zombie in our 
>basement, that is, there is no need to create a second one?
>Yours sincerely,
>Dieter Fensel
>Scientific Director of DERI
>Dieter Fensel, http://www.deri.org/
>Tel.: +43-512-5076485/8
Received on Saturday, 20 August 2005 12:08:37 UTC

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