|Date:||Fri, 20 Apr 2007 17:39:21 +0100|
Dear Leo et al,
First, I think this is a really good place to start a discussion from, and I appreciate the work in putting this together.
Unfortunately, I am not able to be at the summit, so I will have to make my comments off-line. Hopefully someone will pick them up and make sure they are represented during the discussions.
First, one of my hopes for this document is that it would be possible to hand it to a lay person (say my bosses bosses boss, who would probably reach for a dictionary when hearing the word ontology, and has an aversion for long words) such that they would say at the end "OK I can see what that is about". This means eventually simpler language... When we get there it is ready for Wikipedia.
Taking the document a section at a time:
Pinciples: Looks fine.
1. There are at least two important word senses for 'ontology': ontology as a field of study "ontology (philosophy)" and ontology as a technology for computer and information scientists. We are talking about the second sense of the word, "ontology (computer science)".
I'm in the camp that says we need an inclusive sense of ontology across philosophy and computer science. I for one find myself doing one thing that involves both philosophy and computer science, it would not make sense to me to think that there were two different sorts of things that I was doing.
2. Ontology could refer to either (1) a piece of information that can be talked about objectively, communicated in digital media, and shared without loss of information among a community; or (2) a set of ideas, concepts, abstractions, or other entities that are not the same as the representations or descriptions of them. We propose that we limit our discussions to the first sense: ontology as an objective form. The other sense is called a conceptualization.
I'm not sure I follow this. Let me try putting this another way round. With ISO 15926 we are increasingly reaching the conclusion that we need to be able to publish the ontology in different formats. We already have EXPRESS and OWL, and no doubt will add CLIF in due course. Are these different representations of ISO 15926 to be considered different ontologies? Or are they different representations of the same ontology? (I would prefer the latter). Of course an ontology needs to have at least one representation.
3. In the context of computer and information sciences, an ontology is a specification of a conceptualization. That is, it specifies the concepts, ideas, relations, abstractions, and so forth in an objective form. The intent is to clarify the meaning, enabling shared understanding. This is the conventional sense of specification in computer science, analogous to the terms requirements specification, database specification, and program specification. In the context of knowledge representation in particular, an ontology specifies the conceptual primitives for representing a domain, in the same way that a database schema specifies the relations used in a database, and a programming language provides the primitives used in an implemented algorithm.
I agree with Mike Uschold's comments on this. Either specification is the wrong word (I would suggest representation) or the sense used in requirements specification is misplaced. But as above, I think this is too narrow a position to be taking, even from a computer science point of view.
4. An ontology provides a specification of a conceptualization by defining a representational vocabulary -- a set of terms that can be used to represent the domain -- together with constraints on their meaningful use. The representational vocabulary may include concepts or categories, relations, properties, or other primitives for representing knowledge. The "content" of this specification includes:
· Identification of the fundamental categories in the domain
· Identification of the ways in which members of the categories are related to each other
· Constraints on the ways in which the relationships can be used
Well actually, it does not necessarily define a vocabulary. One approach is to define just a set of concepts, which may have multiple names in - e.g. different languages. The formal identity of the concept might be an integer. Thinking of integers as terms, is I think stretching it a little.
I like the bullets, but the third one doesn't sound quite right. How about "Constraints that apply to things covered by the ontology." or some such.
6. It does not matter to this definition whether an ontology is formally equivalent to a logical theory, whether there is a formal difference between an ontology and a knowledge base, or whether an ontology is only definitional or also contains axiomatic constraints. In fact, it is not necessary that the ontology be represented in any kind of logical formalism. Many highly successful specifications (eg, the HTTP standard) are given only in natural language, yet can be enforced with machine-understandable tests and examples. What matters is that its purpose is to specify a conceptualization, in what ever representational form is appropriate.
I like this a lot (well apart from the language of the last sentence).
An ontology, for computer and information sciences, is a specification of a conceptualization, which is the set of ideas, concepts, relationships, or other abstractions that comprise a domain of modeling or discourse. An ontology defines a representational vocabulary for the conceptualization, and specifies constraints on the meaningful use of this vocabulary, so that facts about the domain can be shared, communicated, and reasoned about.
I'm in the camp that does not like this definition I'm afraid. It is too narrow and too long winded. For what it is worth, my personal favourite is:
"A theory of what exists."
I like it because it is both short and accurate, and is, for example, neutral on whether we are talking about a conceptualisation or not. However, for our purposes I might want to elaborate slightly because "theory" and "exists" are used in slightly technical ways, so that it is clear that theory includes rules, constraints and types of things.
Kinds of Ontology
I find it hard to distinguish between the Level of Structure, and the Representational granularity as they are presented. To me they seem to amount to the same thing. As to the language, it seems to me that just acts as a constraint on what can be said, where as the other two are about what is said, and having an expressive language does not mean that the full expressivity has been used. So really I think that expressiveness is just a red herring.
I suggest there are two dimensions:
Concept granularity - how finely divided are the concepts and how many of them are there. Are they few and broad, or many and specific How deep are the specialization hierarchies relative to the number of objects in the domain it covers.
Rule Completeness - how many of the valid rules and constraints are captured in the ontology. (This is linked to the use of expressiveness available in the language).
Intended Use - Looks good.
Role of automated Reasoning - isn't this an intended use?
Descriptive vs Prescriptive - An important distinction I think. I would say revisionary rather than prescriptive. I would use prescriptive for something that was being intentionally defined - this ontology defines how these things are because this is their definition.
Design Methodology - I think there is much more that could be said here
Yes these look fine.
I'm not sure that there are any databases that do not have ontological content. If you are talking about sales, you need the products you sell and their properties, the classification of the types of sale and typs of customer etc. which the ground level transactions need to be classified by if you are to be able to extract any useful information from them. I suppose a database that consisted only of one table (no relationships) and just free form text fields you can put what you like in would be free of an ontological content, but then I'm not sure I would call that a database either.
Examples to discuss
An internet standard is the kind of intentional specification ontology I was referring to earlier (so are most other standards).
Box and arrow diagrams are almost certainly ontological in nature - at least they could be.
OK. Well those are my initial thoughts for your consideration.
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