W3C home > Mailing lists > Public > public-rif-wg@w3.org > March 2008

Re: thoughts on metadata

From: Sandro Hawke <sandro@w3.org>
Date: Tue, 25 Mar 2008 10:45:07 -0400
To: Jos de Bruijn <debruijn@inf.unibz.it>
Cc: Michael Kifer <kifer@cs.sunysb.edu>, RIF WG <public-rif-wg@w3.org>
Message-ID: <14620.1206456307@ubuhebe>


> > 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). 

How about "Metalinguistic Constructs"?

And the other kind of "metadata", we might call "Structured Comments".

(not perfect names, but perhaps better?)

The key distinction is that metalinguistic constructs can change rule
engine behavior and structured comments cannot.  (The structured
comments may have machine semantics (like all RDF) when looked at as
data in its own right, but when you're looking at the commented-on
ruleset, they are to be ignored.)

My suggestion at one point was to note the difference in the fallback
information.  Removing structured comments has zero impact on soundness,
completeness, or performance.   Removing these other things does have
semantic impact of some sort.

  -- Sandro

> 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.
> 
> 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 string
> s.
> > 
> > 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/
> ----------------------------------------------
> One man that has a mind and knows it can
> always beat ten men who haven't and don't.
>    -- George Bernard Shaw
> 
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Received on Tuesday, 25 March 2008 14:45:43 GMT

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