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Re: thoughts on metadata

From: Michael Kifer <kifer@cs.sunysb.edu>
Date: Tue, 25 Mar 2008 19:39:44 -0400
To: Jos de Bruijn <debruijn@inf.unibz.it>
Cc: RIF WG <public-rif-wg@w3.org>
Message-ID: <28678.1206488384@cs.sunysb.edu>


> > I think the current proposal for meta data is inadequate for the current
> > and future needs because it is not part of the syntax of the language, its
> > proposed is too limited, and in the current form it cannot be given a
> > semantics.
> 
> Right.  That is why I also proposed the "directives" [1] (even though 
> the term is probably not appropriate; so if you have anything better). 
> The examples you mentioned are actually good examples of the kinds of 
> things directives can be used for.  So, we have the current list of 
> examples for the use of directives:
> 
> These are the ones we I think we really want to have in BLD:
> 
> - import of RIF rule sets
> - reference to external data sources (e.g. RDF)
> - reference to external data models (e.g. RDFS/owl)
> 
> These are things to keep in mind for extensions of BLD:
> 
> - sorting of query answers
> - priorities
> - preferences
> 
> If we would need variables in directives, extensions to BLD can extend 
> the notion of "directive".
> 
> Note that still the same discussion (we've had already several times) 
> applies: whether we want to have a generic syntax element "directives" 
> or whether we want to extend the syntax for each of the possible directives.

OK. But the more general syntax should then be added to FLD -- to keep us
honest.

Also, this still does not address the issue that the meta syntax is not
accessible to processing by rules.


	--michael  


> Best, Jos
> 
> [1] http://www.w3.org/2005/rules/wiki/Annotations
> 
> > 
> > Here are some concrete problems.
> > 
> > 1. Meta data can be attached to various parts of the rules, not just rules
> >    themselves, and this metadata can affect the semantics.
> >    A simple example is specifying that the output to a query must be sorted.
> >    This changes the semantics, since the answer is not a set any more
> >    but a list.
> > 
> > 2. Some important types of rule systems are based on prioritized defaults
> >    (defeasible, courteous, preference LP).
> > 
> >       - Here metadata is part of the syntax and of semantics.
> >       - Typically metadata consists of rule labels and priority or
> >         preference information.
> >       - Metadata items are often *terms with variables* and not just strings.
> > 
> > 3. The current proposal does not offer any obvious or natural way for the
> >    metadata to be processable by a (possibly different) rule set.
> > 
> >    
> > 
> > 
> > 	--michael  
> > 
> 
> -- 
>                           debruijn@inf.unibz.it
> 
> Jos de Bruijn,        http://www.debruijn.net/
Received on Tuesday, 25 March 2008 23:40:40 GMT

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