WebOnt Candidate Core Requirements

Last modified: 12/13/01

The following list contains the requirements under consideration. For each requirement a short definition is provided. Some requirements also include additional issues.

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.
Issues:

• a) What does this mean? Import all axioms wholesale into new ontology? Include definitions but don't allow them to be redefined or restricted? Simply reuse names but not definitions?
• b) How does this relate to inheritance?

R3. Ontology evolution

Ontologies can be changed over time and data sources can specify which version of the ontology they commit to.
Issues:

• a) How does this differ from ontology extension (R2)? In R2, the original ontology is unchanged.
• b) Pat believes that this needs a deeper analysis of the meanings of URIs

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."
Issues:

• a) This requirement needs to be balanced with scalability (R6).
• b) Pat believes this is beyond state of the art.

R5. Inconsistency

Different ontologies may be contradictory, or different data sources may be contradictory. It should be possible to detect inconsistencies.
Issues:

• a) Since inconsistency will probably be inevitable on the Web, we should probably also provide means for continuing reasoning in the face of inconsistency. However there is disagreement about this issue.

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.
Issues:

• a) Should this be specified for a fact in a data source, or for a property in an ontology?
• b) How is this different from R8? Ontologies changes have deeper repercussions than data source changes, because many sources may depend on a single ontology for definitions. Furthermore, ontologies change more slowly than data.
• c) Perhaps rename requirement to time validity?

R9. Security

Ability to specify who can view and modify information. Have ontologies that can specify access control information.
Issues:

• 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"
• c) Is it possible that future protocols will allow the delivery of parts of ontologies, to which access control can be applied?
• d) Deb believes that viewing portions of objects, abstractions of objects, and objects themselves fits our charter

R10. XML syntax

The language should have an XML serialization.
Issues:

• a) Must it also build on RDF?

R11. Internationalization

The language should support ontologies in multiple languages.
Issues:

• a) Is this already covered by interoperability (R4)? There has been a suggestion to remove this requirement and mention it as an issue under R4.
• b) Character set issues are already handled by XML
• c) Are there special fields that would be useful for international uses?
• d) Should this be renamed to "multi-lingual ontologies?"

R12. Ontology-based search

Ability to locate information using the ontology to structure queries? Or is this something else?
Issues:

• a) Is this searching for content (information retrieval) or for valid inferences (logical deduction)?
• b) Proposal to define this as "the ontology language offers a semantic level of description of information on the Web that allows queries to be formulated independently from XML serialization, on the basis of the meaning of the information."
• c) Findur is a possible example

R13. Ontology querying

Ability to ask questions about the logical structure of the ontology? Or is this something else?
Issues:

• a) Are R12 and R13 the same requirement? Maybe R12 is information retrieval and R13 is question answering? There is some support for the later idea.
• b) Is this maybe the need for a standard query language?
• c) Need to distinguish between asking questions about the structure of an ontology and asking questions about what follows from the ontology

R14. Expressiveness

What can be expressed in the language and what reasoning capabilities should be expected in systems that fully implement it.
Issues:

• a) What is the right balance between expressiveness and scalability (R6)?

R15. Proof checking

Proofs can be described in the language and will be checkable.
Issues:

• a) There is a proposal to rename this to explainable.

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.

R17. Tagging

It is sometimes useful to attach additional information to a piece of data. For example, the source of the data, a time stamp, or a confidence level. Tagging is the ability associate such information.