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Re: Proposed response to Golbeck regarding imports issue

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Fri, 20 Jun 2003 10:16:00 -0400
Message-ID: <3EF31720.E84FC333@cse.lehigh.edu>
To: Jim Hendler <hendler@cs.umd.edu>
CC: WebOnt <www-webont-wg@w3.org>

Deletions accepted. Message sent.

Jeff

Jim Hendler wrote:
> 
> Jeff - I think you have some gratuitous comments in here - in
> particular, I don't find your workaround of copying parts of a file
> but using the original URI to make great sense - better not to go
> there.  Ditto for suggestion that she should come up with something
> for OWL 2.0 -- let's delete these. Everything else looks fine - so if
> you accept my deletions, you should send the following
>   -JH
> 
> Dear Ms. Golbeck,
> 
> Thank you for you comment. As the original issue owner for imports, I
> have been asked to respond on this issue to you. This issue was heavily
> debated by the working group between Sept. and Nov. 2002 (see the public
> archive for excruciating details) and it became clear that any
> resolution (including not including imports at all) would have been
> closed over objection. The current resolution is the result of a
> majority vote.
> 
> That being said, let me address your specific concerns because I believe
> there are suitable workarounds for your issues.
> 
> You mention your desire to break the NCI ontology into smaller
> ontologies. This certainly would be a good reason to use imports.
> You claim that your particular ontology is so interconnected that
> it cannot be modularized in a way that doesn't result in every file
> importing every other file. However, this is still better than one big
> file, because it will benefit many tools. Imports only really matters to
> reasoners, and even then only those that are concerned with
> completeness. We will add the following text to "OWL Web Ontology
> Language 1.0 Reference" to make this clear:
> 
> "Note that whether or not an OWL tool must load an imported ontology
> depends on the purpose of the tool. If the tool is a complete reasoner
> (including complete consistency checkers) then it must load all of the
> imported ontologies. Other tools, such as simple editors and incomplete
> reasoners, may choose to load only some or even none of the imported
> ontologies."
> 
> You also mentioned wanting to borrow a single term from a large
> ontology, without having to import the whole thing. This was discussed
> by the working group from the very beginning. I point to Objective 07
> from the Use Cases and Requirements document [1]:
> 
> O7. Commitment to portions of ontologies
> The language should support the ability to commit to portions of an
> ontology, as well as committing to an entire ontology. However, it is
> unclear what granularity should be used here. Possible choices are to
> choose a subset of concepts with their entire definitions, or to
> choose   individual pieces of definitions. Note that borrowing partial
> definitions of concepts must address the potential interoperability
> problems that can arise since different applications will be using the
> same identifier to mean different things.
> 
> Note, as an objective, the group decided that the feature was generally
> desirable, but that it wasn't absolutely necessary for the the first
> version of the language. It was discussed at the time imports was
> considered, but no concrete proposal for how partial imports would work
> was put forward at that time.
> 
> Finally, you mention the wording in the documents:
> 
> First you discuss the following passage from the OWL Reference document,
> 7.3:
> 
> "Note that the importing a document is different than creating a
> namespace reference. owl:imports do not set up a shorthand notation for
> names as does a namespace reference. On the other hand, the namespace
> reference does not imply that all (or even any) ontological terms from
> that namespace are being imported. Therefore, it is common to have a
> corresponding namespace declaration for any ontology that is
> imported."
> 
> You are correct that there are a few problems here: First, we are
> inventing the term "namespace reference" when we mean "namespace
> declaration." Second, the point of this paragraph was to comment on why
> namespace declarations and imports are both needed, not to comment on
> how systems might follow links. In particular, we were trying to say
> that they are very different animals. I suggest the following rewording:
> 
> "Note that although owl:imports and namespace declarations may appear
> redundant, they actually serve very different purposes. Namespace
> declarations simply set up a shorthand for referring to identifiers.
> They do not implicitly include the meaning of documents located at the
> URI. On the other hand, owl:imports does not provide any shorthand
> notation for referring to the identifiers from the imported document.
> Therefore, it is common to have a corresponding namespace declaration
> for any ontology that is imported."
> 
> You also mention the following from the OWL Guide, Section 2.2.:
> 
> "Importing another ontology brings the entire set of assertions provided
> by that ontology into the current ontology. In order to make best use of
> this imported ontology it would normally be coordinated with a namespace
> declaration. Notice the distinction between these two mechanisms.
> The namespace declarations provide a convenient means to reference names
> defined in other OWL ontologies. Conceptually, owl:imports is provided
> to indicate your intention to include the assertions of the target
> ontology. Importing another ontology, O2, will also import all of the
> ontologies that O2 imports."
> 
> Once again, you are correct that the wording could be improved. By "to
> make best use of" we really meant "for convenience of the user." Of
> course, you are also correct that there may be times when the namespace
> declaration is irrelevant (such as the case when an ontology does not
> create any new identifiers), which is why it is important that we say
> "usually" and not always. We plan to replace that paragraph (and the
> preceding one) with the following text:
> 
> "An owl:imports statement references another OWL ontology.  The URI
> that is the value of the rdf:resource attribute identifies the
> ontology to be imported. The current ontology is extended with the
> contents of the referenced ontology. Importing an ontology, O2, will
> also import all of the ontologies that O2 imports.
> 
> Thus, if ontology A imports ontology B, the meaning of terms in A
> are exactly the same as they would be if all of the statements in B
> (including further imports statements) were included in A.
> 
> It is often convenient to coordinate owl:imports with a namespace
> declaration, so that qualified names can be used when referring to the
> resources of the ontology. Notice the distinction between these two
> mechanisms. The namespace declarations provide a convenient means to
> reference names defined in other OWL ontologies, while owl:imports
> indicates an intention to include the assertions of the target
> ontology."
> 
> Thank you again for you comments. Please let me know if I have
> adequately addressed your concerns.
> 
> [1] http://www.w3.org/TR/webont-req/#section-objectives
> --
> Professor James Hendler                           hendler@cs.umd.edu
> Director, Semantic Web and Agent Technologies     301-405-2696
> Maryland Information and Network Dynamics Lab.    301-405-6707 (Fax)
> Univ of Maryland, College Park, MD 20742          *** 240-277-3388 (Cell)
> http://www.cs.umd.edu/users/hendler      *** NOTE CHANGED CELL NUMBER ***
Received on Friday, 20 June 2003 10:16:11 GMT

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