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WebOnt Requirements - Summary

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Tue, 11 Dec 2001 15:40:13 -0500
Message-ID: <3C166F2D.F44E9230@cse.lehigh.edu>
To: herman.ter.horst@philips.com, dlm@ksl.stanford.edu, phayes@ai.uwf.edu, jos.deroo.jd@belgium.agfa.com, jjc@hplb.hpl.hp.com, ned.smith@intel.com
CC: Jim Hendler <hendler@cs.umd.edu>, www-archive@w3.org
We've had a lot of discussion over the last 24 hours, so I thought it
would be useful to try to summarize where we stand. Be warned that this
message is somewhat lengthy.

One issue that has come up is whether we should be considering only
requirements for a certain "layer" of the Semantic Web. I believe that
it is useful if we identify all requirements for an ideal semantic web
language. We can then divide these into which are more appropriate for
RDF, or for a yet to be named Proof layer.

I have tried to gather all of the proposed requirements and issues from
our discussion into a single list, which is at the bottom of this
message. I've numbered each requirement and attempted to provide a short
description of it. Additionally, I've included open issues for many
requirements, and assigned letters to these issues. If you'd like to
propose a change to a requirement or add an issue, please refer to it by
number (e.g., R6). If you'd like to respond to or comment on an issue,
please refer to it by number and name (e.g., R2.b). I'll try to maintain
this list as discussion continues. I don't expect that we'll solve all
these issues anytime soon, but I think at least having them gathered
together will help us focus on the job at hand. If you add a requirement
or issue, assign it the next number or letter.

I request that we have a straw poll on the requirements that we have so
far. For each requirement, I'd like to know whether you support it (even
though it may be out of scope), are against it, or are undecided. It may
be useful to provide a short explanation for your negative votes. Also,
feel free to state whether or not you think each requirement is in the
scope of the WebOnt effort. I want to eventually produce two lists: one
a list of requirements we think are important for WebOnt and a list of
requirements we think are important but are out of scope of this effort.
Then we can focus on writing up those requirements that are important
and in scope.




WebOnt Candidate Requirements

R1. Shared ontologies
Ontologies are publicly available and different data sources can commit
to the same ontology for shared meaning.

R2. Ontology extension
Ontologies can be extended by other ontologies in order to provide
additional definitions.
a) Import all axioms wholesale into new ontology?
b) Include definitions but don't allow them to be redefined or
c) Simply reuse names but not definitions?

R3. Ontology evolution
Ontologies can be changed over time and data sources can specify which
version of the ontology they commit to.
a) How does this differ from ontology extension (R2)? In R2, the
original ontology is unchanged.

R4. Ontology interoperability
Different ontologies may model the same concepts in different ways. The
language should provide primitives for relating different
representations, thus allowing data to be converted to different
ontologies, and enabling a "web of ontologies."

R5. Inconsistency
Different ontologies may be contradictory, or different data sources may
be contradictory. It should be possible to detect inconsistencies. 
a) Since inconsistency will probably be inevitable on the Web, we should
probably also provide means for continuing reasoning in the face of

R6. Scalability
The language should be able to be used with large ontologies and large
data sets.

R7. Ease of Use
The language should provide a low-learning barrier and have clear
concepts and meaning. The concepts should be independent from syntax.

R8. Data persistence
The Web is constantly changing, so it would be useful to know the
lifetime of information. This will be useful for agents to know when
they must refresh their knowledge bases.
a) Should this be specified for a fact in a data source, or for a
property in an ontology?

R9. Security
Ability to specify who can view and modify information. Have ontologies
that can specify access control information.
a) Web typically doesn't allow update (except via file update) and
viewing web pages is typically all or nothing, so how is this relevant?
b) Some have argued that security is essential and should be seen as a
vertical slice in the "layer cake"

R10. XML syntax
The language should have an XML serialization.
a) Must it also build on RDF?

R11. Internationalization
The language should support ontologies in multiple languages.
a) Is this already covered by interoperability (R4)?
b) Character set issues are already handled by XML

R12. Ontology-based search
Ability to locate information using the ontology to structure queries?
Or is this something else?
a) Is this searching for content (information retrieval) or for valid
inferences (logical deduction)?

R13. Ontology querying
Ability to ask questions about the logical structure of the ontology? Or
is this something else?
a) Are R12 and R13 the same requirement? May R12 is information
retrieval and R13 is question answering?
b) Is this maybe the need for a standard query language?

R14. Expressiveness
What can be expressed in the language and what reasoning capabilities
should be expected in systems that fully implement it.
a) What is the right balance between expressiveness and scalability

R15. Proof checking
Proofs can be described in the language and will be checkable.

R16. Trust
How to determine which information is reliable and/or believable. Must
be able to know the sources of information and to express what
supporting information is needed to believe something.
Received on Tuesday, 11 December 2001 15:40:30 UTC

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