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Re: RIF Working Group needs namespace name for xpath "op"

From: Jos de Bruijn <debruijn@inf.unibz.it>
Date: Thu, 17 Apr 2008 12:28:34 +0200
Message-ID: <48072652.7010502@inf.unibz.it>
To: public-qt-comments@w3.org
CC: Sandro Hawke <sandro@w3.org>
Dear all,

Has my explanation of the need for RIF to identify functions and 
comparators been satisfactory?

To come back to the original question of Sandro [1]:
Can we pick a namespace to use for naming functions and comparators that 
are currently not named?

The original proposal by Sandro was:

Best, Jos

[1] http://lists.w3.org/Archives/Public/public-qt-comments/2008Mar/0021.html

Jos de Bruijn wrote:
> Hello,
> This is an e-mail sent in reply to the thread starting here [1].
> I am a member of the RIF working group and involved with the technical
> design of the language.
> RIF is a logical language for exchanging rules over the Web, essentially
> based on predicate logic.  As such, the main building blocks of the
> language are constants, functions, and predicates. Predicates are
> essentially relations.
> Constants and functions may only be used inside predicates. Different
> predicates may be composed using logical connectives such as and, or,
> and implication.
> Therefore, RIF is a relational language (in contrast to, e.g., xpath,
> which is a functional language).
> Most of the predicates, functions, and constants used in rules are
> provided by the user, so RIF cannot say how they should be interpreted.
> However, in any practical rule language (including RIF) there are some
> "built-in" predicates and functions, which have a defined meaning.
> These built-ins are typically concerned with concrete data values (e.g.,
> integers, strings), and include such things as numeric comparison and
> substring matching.
> Now, XML schema defines a number of built-in datatypes that are of
> interest to RIF.  In the interest of reusing existing standards and
> since using XML schema built-in datatypes is generally recommended for
> semantic Web languages (e.g., RDF and OWL), we decided to use XML schema
> built-in datatypes for the representation of concrete values in RIF.
> Since we want to enable users to manipulate and compare concrete data
> values, we want to include built-in functions and predicates that work
> on XML schema built-in datatypes.
> The "XQuery 1.0 and XPath 2.0 Functions and Operators" document defines
> a number of functions and a number of comparators on XML schema built-in
> datatypes.  Since we are interested in reusing existing standards and
> avoiding duplication of effort, we want to adapt a number of these
> functions and comparators to our context (e.g., a comparator with an
> xsd:boolean return value becomes a built-in predicate in RIF) and use
> them in RIF.
> Since RIF is a Web language, we want to use IRIs to identify these
> built-ins.  Now, the "XQuery 1.0 and XPath 2.0 Functions and Operators"
> document defines IRIs for a number of the functions and comparators, but
> not for all of them.  For example, the numeric-add function does not
> have an IRI. So, our problem is: which IRIs should be used to refer to
> such functions and comparators?
> It has been suggested in the thread starting with [1] that we could add 
> specific symbols (e.g., >) to our language for such "IRI-less" functions 
> and comparators.  However, I do not really see a justification for 
> adding symbols to the language for specific built-in functions, but use 
> IRIs for others.  I think the language should be uniform and use IRIs to 
> identify any built-in predicate or function.
> Finally, if we were to introduce the same symbols for functions and 
> comparators as xpath does, the operators are polymorphic, which is 
> undesirable for us because we want to RIF processors to be able to see 
> from a rule sets which datatypes and built-ins it needs to support to 
> process the ruleset, and polymorphic operators would require processors 
> to implement all the underlying data types and built-ins.
> Best, Jos
> [1] 
> http://lists.w3.org/Archives/Public/public-qt-comments/2008Mar/0021.html

Jos de Bruijn            debruijn@inf.unibz.it
+390471016224         http://www.debruijn.net/
Only two things are infinite, the universe and
human stupidity, and I'm not sure about the
   -- Albert Einstein

Received on Thursday, 17 April 2008 10:29:02 UTC

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