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Re: abstract class

From: pat hayes <phayes@ai.uwf.edu>
Date: Thu, 6 Feb 2003 13:26:38 -0600
Message-Id: <p05111b0aba68661b8017@[10.0.100.86]>
To: marc@jfcarrion.com
Cc: Brian McBride <bwm@hplb.hpl.hp.com>, www-rdf-comments@w3.org

>--- Brian McBride <bwm@hplb.hpl.hp.com> wrote:
>>  At 03:12 24/01/2003 -0800, Marc Carrion wrote:
>>
>>  [...]
>>
>>  >   That would be illegal if you don't have any
>>  other
>>  >information. But if you have had:
>>  >     x rdf:type c .
>>  >     c rdf:type rdfs:Abstract .
>>  >     x rdf:type a .
>>  >     a rdf:subClassOf c .
>>  >   That would be correct.
>>
>>  Built into RDF is the assumption that any subgraph
>>  of an RDF graph is a
>>  legal RDF graph.  That's not likely to change
>>  anytime soon.
>>
>    When using reification
>      _:xxx rdf:type rdf:Statement .
>      _:xxx rdf:subject <ex:a> .
>      _:xxx rdf:predicate <ex:b> .
>      _:xxx rdf:object <ex:c> .
>    would be true, but if we only have
>      _:xxx rdf:type rdf:Statement .
>      _:xxx rdf:subject <ex:a> .
>      _:xxx rdf:predicate <ex:b> .
>    that would not be a 'correct' model, I mean it's
>going to have a wrong Resource of type Statement.

No, not exactly. It is incomplete, not wrong. If I tell you that I 
have a head and two arms, you shouldn't conclude that I don't have 
any feet. The second graph *tells* you that _:xxx is of type 
Statement, so you (ought to) know that it *has* an object - they all 
do - but you just don't (yet) know what it is. RDF information is 
always potentially incomplete in this sense.

>
>    The same when using Collections
>      _:c1 rdf:type rdf:List .
>      _:c1 rdf:rest _:c2
>    which is a List without head, it's a correct Model
>but an incorrect List

No, it is a list and you don't (yet) know what its head is. You know 
it is a list, however, since the first triple tells you it is.  RDF 
never gives you *definitions* in a strict sense, it only gives you 
*descriptions* (which might or might not be complete enough for you 
to figure out something you need to know, such as what the head of a 
list is.)

Pat Hayes

>
>    I was thinking that Abstract Classes could be
>defined in the same way.
>
>    Regards,
>            Marc
>
>=====
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Received on Thursday, 6 February 2003 14:26:43 GMT

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