Re: [ontoweb-list] A Comparison of RDF Query Languages

From: Vassilis Christophides (christop@ics.forth.gr)
Date: 04/30/04

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    Hi Andreas

Thanks for the mail. I would like to comment three of your criteria
employed in RQL evaluation:

1) Recursion: Actually RQL supports recursion on the schema, e.g., 
   select $X from Publication{$X} will return not only direct but also
   transitive subclasses of Publication.

   Another example is the basic query nca(Class1, Class2) returning
   the nearest common ancestor of Class1 and Class2 in a class
   subsumption hierarchy.

   On the other hand RQL do not support recursive data queries, e.g., 
   select X,Y from  {X}SubTopic*{Y}

   So RQL supports a restricted form of recursion according to your
   terminology. 

2) Value Space: XML Schema datatypes are captured directly by the RQL
   semantics e.g., 
   select X from {X}pages{Y} where Y = 8
   and there is no need to cast strings to integers in queries
   ("8"^^<xsd:int>)

   So RQL supports Value Space queries for all XML base types

3) Collection and Containers: RQl not only provides the ability to
   query bugs and sequences, for instance, returned by nested queries
   e.g.  select Y from (Person intersect Human){X}, {X}name{Y}

   but also to construct explicitly new container values e.g.,
   seq(domain(pages), range(pages)[0]

   So I don't understand the justification of the restricted RQL
   support of containers in your report.

Best

Vassilis

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