cubicweb #509109 transitivity of relationships [open]

A relation R is transitive if R(a,b) and R(b,c) implies R(a,c). Having a 'transitive' property for relations would make it easier to deal with hierarchies for example. We would say "descendant_of: subject='Keyword', object='Keyword', transitive=True" and there would be no need to define the hooks that compute all the implications of a new relation as we do now.

prioritynormal
typeenhancement
done in<not specified>
load2.000
load left2.000
closed by<not specified>

Comments

  • 2009/11/09 14:38

    I've changed child_of to descendant_of in the example above (better suited to the examples : my grandchildren are not my children).

    I think that we need to be careful here. Transitivity is wonderful in math but ends up being tricky in real life. If you define a truly transitive relation, won't you need pretty soon to be able to restrain it to a single depth level? For instance in a classification scheme such as:

    class Category:
    in_category = SubjectRelation('Category', transitive=True)

    I think it's only when searching that transitivity comes into play: when working with my hierarchy I'm mostly interested by the immediate neighbour levels (above and under the level in use) : I don't want to see that my category is ultimately in the top-level category of my ontology, nor am I interested in all the sub-sub...categories.

    • 2009/11/09 16:54, written by nchauvat

      yes, making a difference between _descendant_of (the relation in the schema, that you call child_of above) and descendant_of (the computed relation) is needed:

      X _descendant_of Y.
X descendant_of Y :- X _descendant_of Y.
X descendant_of Y :- X descendant_of Z, Z _descendant_of Y.
  • 2010/07/21 13:40, written by acampeas

    Any Y WHERE Y transitive_closure_of(child_of) X ? :)

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Ticket #509109 - latest update on 2010/07/21, created on 2009/11/08 by Nicolas Chauvat