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

From: Vassilis Christophides (
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
    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
       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.

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