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Re: FWD: RE: OWL S&AS Comment - owl:imports (fwd)

From: Jennifer Golbeck <golbeck@cs.umd.edu>
Date: Fri, 20 Jun 2003 15:48:35 -0400 (EDT)
To: <heflin@cse.lehigh.edu>
Cc: <public-webont-comments@w3.org>
Message-ID: <Pine.SOL.4.33.0306201534030.7295-100000@laffytaffy.cs.umd.edu>



Thanks for your response. Most tools that I've run into import full
ontologies at this point. Hopefully, as the semantic web matures, they
will move away from this process.

This response adequately addresses my comments (even it it doesn't fix
anything).

Thanks,
Jen






>>===== Original Message From Jeff Heflin <heflin@cse.lehigh.edu> =====
>Dear Ms. Golbeck,
>
>Thank you for you comment. As the original issue owner for imports, I
>have been asked to respond 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.
>
>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,
>Section 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
>using the term "namespace reference" when we really 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 respond to this mailing list to
>let me know if I have adequately addressed your concerns.
>
>Jeff Heflin
>
>[1] http://www.w3.org/TR/webont-req/#section-objectives
>
>
>golbeck wrote:
>>
>>  We have some concerns with the semantics of owl:imports:
>>  1) While clear, it doesn't have a desirable behavior in many, if not most
>>  cases
>>  2) There is no alternative mechanism for sharing parts of ontologies, and no
>>  place holders for such
>>  3) The explication in the Reference and Guide is confusing
>>
>>  Concerns 1) and 2) were inspired by our work on converting the NCI
>terminology
>>  from its proprietary XML format to OWL. The resulting file (viewable at
>>  http://www.mindswap.org/CancerOntology) is 46MB and, because of the size,
>has
>>  broken nearly every existing tool we have tried to use.
>>
>>  One  solution we considered was breaking the terminology into different
>files.
>>  However, since the concepts defined therein are interlinked, each subfile
>>  would have to import all others. Because the current behavior of imports
>joins
>>  all terms from the imported ontologies, the separate files actually offer no
>>  size solution.
>>
>>  When creating their own files, users may want to borrow a single term from a
>>  large ontology. With the current function of "imports", a small file that
>uses
>>  one term from cyc would become huge. As the semantic web becomes
>increasingly
>>  interlinked, a file with only a handful of concepts and a few imports could
>>  easily grow to be several gigabytes because of cascading includes.
>>
>>  To address this issue, we would like to see an alternative that allows users
>>  to import only specific elements of an ontology.
>>
>>  3) With respect to specific documents:
>>
>>  >From OWL Reference, 7.2: """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."""
>>
>>  What is "creating a namespace reference"? It seems like you're confusing two
>>  different levels, the imports, which takes place at the *ontological* (or
>>  "graph") level, and the document level (i.e., where people write out the
>>  ontology). Furthermore, *namespace* declarations aren't the only way one can
>>  "suggest" important. Presumably *using* a term from some other ontology (via
>a
>>  uriref in an rdf:about or rdf:resource, or, higher level, as one side of an
>>  equivalence or subClass|PropertyOf relation. (There are folks who have
>written
>>  tools that try to import ontology documents that are "at" any URI mentioned
>in
>>  the current document.)
>>
>>  >From OWL Guide, 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."""
>>
>>  "In order to make best use..."? All the namespace declaration *can* get you
>is
>>  some syntactic shortcuts. It's as if you'd written, "In order to make best
>use
>>  of an imported ontology it would normally be coordinated with an entity
>>  declaration." Furthermore, in some "breaking the file up into pieces"
>>  situations, the ontology uri might not be the "namespace" of some, many, or
>>  even most of the terms in that ontology (e.g,. you import ontology A which
>>  merely imports B, C, D, and E -- i.e., it's a convenience). In other words,
>an
>>  ontology's uri doesn't have any necessary (or necessarily likely) connection
>>  to a prefixing substring of its terms' uris. And that's what's needed for
>the
>>  namespace dec to be useful. There's no scenario in which it affects what you
>>  can do, or do well, from the semantic point of view.
>>
>>  -Jennifer Golbeck and Bijan Parsia

-- 
Received on Friday, 20 June 2003 15:52:03 GMT

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