[Pellet-users] Internal Triple Representation of owl:unionOf (a b) as rdf:List

[Evren Sirin]

On 2/7/08 5:31 AM, Wolfgang May wrote:
> Hi,
>
> constructs like 
>  :Person a owl:Class; owl:unionOf (:Male :Female).
> are translated to collections/rdf:List constructs.
> Although, pellet seems not to "know" that this these things are
> rdf:Lists:
>
> ***
> @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
> @prefix owl: <http://www.w3.org/2002/07/owl#>.
> @prefix : <foo://bla/>.
>
> :Male a owl:Class.
> :Female a owl:Class.
>
> :Person a owl:Class; owl:unionOf (:Male :Female).
> :EqToPerson a owl:Class;
>   owl:unionOf 
>   [ a rdf:List; rdf:first :Male;
>     rdf:rest [ a rdf:List; rdf:first :Female; rdf:rest rdf:nil]].
> :x a :Person.
> ***
>
> ***
> prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
> prefix owl: <http://www.w3.org/2002/07/owl#>
> prefix : <foo://bla/>
> select ?X ?Y ?Z
> from <file:union-list.n3>
> where {?X rdf:first ?Y . OPTIONAL {?X rdf:rest ?Z}}
> ***
>
> results -as expected- in
>
> --------------------------------------------------------------------------------
> | X    | Y                  | Z                                                
> ================================================================================
> | _:b0 | <foo://bla/Male>   | _:b1                                             
> | _:b2 | <foo://bla/Male>   | _:b3                                             
> | _:b3 | <foo://bla/Female> | <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> |
> | _:b1 | <foo://bla/Female> | <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> |
> --------------------------------------------------------------------------------
> Successfully printed 4 query results.
>
> But, if I ask whether ?X is a list, the answer to
>
> ***
> prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
> prefix owl: <http://www.w3.org/2002/07/owl#>
> prefix : <foo://bla/>
> select ?X ?Y ?Z
> from <file:union-list.n3>
> where {?X a rdf:List; rdf:first ?Y . OPTIONAL {?X rdf:rest ?Z}}
> ***
>
> is only
>
> --------------------------------------------------------------------------------
> | X    | Y                  | Z                                                
> ================================================================================
> | _:b0 | <foo://bla/Female> | <http://www.w3.org/1999/02/22-rdf-syntax-ns#nil> |
> | _:b1 | <foo://bla/Male>   | _:b0                                             
> --------------------------------------------------------------------------------
> Successfully printed 2 query results.
>
>  
> Obviously, for 
>   owl:unionOf (...) 
> the list *structure* is generated, but rdf:type rdf:List
> is not assigned.
>
> Is there a reason for this 

The lists used inside concept expressions are part of the built-in 
syntax and are not treated part of the data (ABox). The above queries 
simply query the asserted triples and that is why second query returns 
less answers.

> (from a previous post, I already learnt
> that rdf:first and rdf:rest cannot be used for reasoning)? 

In OWL-DL, it is forbidden to use rdf:Lists outside built-in syntax 
elements. This is not a necessary restriction and it is possible that 
these restrictions will be relaxed in OWL 1.1 (see the use case I 
proposed in the OWL WG regarding this [1]). There is still the problem 
of rdf:first being both an object and data property which can be solved 
by punning.
> It would
> be nice for some applications (e.g. analysis of ontologies) to
> have access to these properties for querying and processing 
> collection-based concept definitions.
>   

We'd be interested in hearing such use cases. These use cases help us in 
the OWL WG discussions.

Cheers,
Evren

[1] 
http://www.w3.org/2007/OWL/wiki/Punning#Lists_.28ObjectProperty_.E2.86.94_DatatypeProperty.29


> Best,
> Wolfgang
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