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Re: rdf inclusion

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Tue, 23 Apr 2002 15:28:22 -0400
Message-ID: <3CC5B5D6.3A053E1D@cse.lehigh.edu>
To: tim finin <finin@cs.umbc.edu>
CC: www-rdf-logic@w3.org
Tim,

If you refer to a term in an ontology without importing then I suggest
that you are using a name without agreeing to its definition. This is
not an error condition, but it may mean that DAML+OIL-compliant agents
won't conclude everything you intend them to. Now, if the user community
feels this is unreasonable, then we can consider having a default
imports that corresponds to each use of a namespace for the upcoming
WebOnt language, but I'm not sure that's the best way to go. I'd be
interested in hearing opinions on this. In any case, I see that WebOnt
needs to do a better job of describing imports and make more explicit
statements about its effects.

As for the diagram, sorry I should have shown how explicit imports links
could help. Of course, the links currently shown are just property
links. I see two ways where imports links could be used to achieve the
desired effect:

method 1:
my-doc daml:imports orig-schema
my-doc daml:imports good-schema

method 2:
my-doc daml:imports orig-schema
orig-schema daml:imports good-schema

Note, these methods assume no other imports statements for the relevant
ontologies. For example, if orig-schema daml:imports bad-schema, then
my-doc could not import orig-schema without accepting the definitions in
bad-schema (since imports is transitive).

Jeff

tim finin wrote:
> 
> 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?  If
> so, is there a reasonable recovery technique, like ignoring
> triples using externally defined terms not imported?
> 
> > ... The problem with using RDF namespaces to decide which schemas are
> > relevant is that multiple files may contain different definitions about
> > the same URI. 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.
> 
> tim
> 
>   ------------------------------------------------------------------------
>  [Image]
Received on Tuesday, 23 April 2002 15:28:45 GMT

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