W3C home > Mailing lists > Public > www-rdf-logic@w3.org > April 2002

Re: rdf inclusion

From: Pat Hayes <phayes@ai.uwf.edu>
Date: Mon, 29 Apr 2002 09:40:46 -0700
Message-Id: <p0510154db8ee15031611@[65.217.30.94]>
To: tim finin <finin@cs.umbc.edu>
Cc: www-rdf-logic@w3.org
>Jeff Heflin wrote:
>>  ... Since I was the initial proponent of daml:imports on the Joint
>>  Committee, let me address this issue. You are absolutely correct that
>>  the imports statement must be used. Simply refering to a namespace does
>>  not include any ontology definitions. You must make the imports
>>  statement explicit. Period. ...
>
>So, what does it mean if one refers to a term in an ontology
>without importing it? Should this be considered an error?

I would say not.

>  If
>so, is there a reasonable recovery technique, like ignoring
>triples using externally defined terms not imported?

In RDF, the official line (as I understand it) is that any published 
RDF which uses a term is (asserted by the publisher of the RDF 
document to be) a true assertion, and anyone who draws any RDF 
conclusion from any combination of such RDF is entitled to conclude 
that the conclusion is true also. That is, publication is assertion, 
and all assertion is unqualified. There is no way to explicitly agree 
or disagree with another piece of RDF.

>  > ... The problem with using RDF namespaces to decide which schemas are
>>  relevant is that multiple files may contain different definitions about
>>  the same URI.

Indeed, but RDF is designed to work in a more perfect world where 
people do not disagree about definitions. Or at any rate, it 
delegates responsibility for dealing with such conflicts to some 
other mechanism.

>See the attached GIF for example. The URI for Dolphin has
>>  additional definitions in two schemas, good-schema and bad-schema. These
>>  definitions are simply rdfs:subClassOf statements that happen to have
>>  orig-schema#Dolphin as their subject. The problem with simply using
>>  namespaces is I can't say that my-doc agrees with the definitions of
>>  Dolphin found in good-schema but not those found in bad-schema. This is
>>  why daml:imports was an essential component of the language. ...
>
>Jeff -- I wonder if you can clarify the situation described by the gif
>image.  In the imports-required case, wouldn't it make sense only if
>my-docs imported orig-schema which subsequently imported good-schema and
>bad-schema? I always assumed that importing was transitive, since the model
>was informally described as "like including the file".  If so, then my-doc
>can't use orig-schema without also committing to both good-schema 
>and bad-schema.

Right; and that would be the RDF assumption also, as I understand it. 
In effect, all other published RDF is implicitly imported. The proper 
way to think about this is not in terms of a lot of isolated 
ontologies, each with its own point of view; but more like a kind of 
global conversation, all the participants in which are using the same 
vocabulary.

Pat Hayes

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Received on Monday, 29 April 2002 12:42:17 GMT

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