Dear John, (01)
This is the right question. (02)
> What is the purpose of an ontology? (03)
MW: My answer to this is that an ontology (computer science artefact) is an
information system, it both is a repository of information and you can query
it to get the answers to questions. (04)
MW: So now we can consider the purpose of information, which in business, is
to support decisions taking (information can also be entertainment or some
combination of the two). Better information leads to better decisions. Where
decisions appear in the processes of an enterprise. (05)
MW: So now we have a basis for evaluating our ontologies. Do they provide
(some of) the information that meets the requirements to support a decision.
Of course there may be more than one decision that the ontology supports,
and this answers the question of scope. The (intended) scope of an ontology
is the set of decisions it is designed to support. (06)
We can now evaluate an ontology in terms of the quality of the information
it provides. Here quality is not better or worse, but meeting agreed
requirements. An evaluation would be around the effectiveness and efficiency
with which these requirements are met. (07)
Some properties that you might consider that determine effectiveness of
information include:
- Relevance - is the information relevant to the decision at hand
- Clarity - is the meaning of the information clear
- Accuracy - how close to the truth is the information?
- Completeness/timeliness - is all the information available when the
decision needs to be made? (08)
Some properties that affect efficiency include:
- Cost - how much does the information cost to provide?
- consistency - is the same thing referred to in the same way? (otherwise
there are costs and timeliness issues of reconciliation) (09)
> But focused on what? Any kind of comparison, including evaluation,
> implies a criterion of some kind: "X is better than Y according to
> some criterion Z."
>
> What criterion Z makes one ontology better than another? (010)
MW: Therefore one ontology is better than another if it meets the
information requirements where the other does not. On the other hand, one
ontology is not better than another if it exceeds the information
requirements. Also if two ontologies meet the information requirements, then
one is better than another if it does so more efficiently, which usually
means at lower cost. (011)
MW: One of the things that falls out from this is that an ontology is not of
poor quality if it fails to meet requirements that were not part of its
specification (you cannot fail to meet unstated requirements). This is often
one of the criticisms of ontologies (it's a bad ontology because it was
designed to do this, but it can't meet my requirement which is that). There
is no reason to suppose an ontology will meet wider requirements than it was
designed to meet, so if you intend it to meet broad requirements, that had
better be part of its design. (012)
MW: So in essence it is all a matter of quality (fitness for purpose). (013)
Regards (014)
Matthew West
Information Junction
Tel: +44 1489 880185
Mobile: +44 750 3385279
Skype: dr.matthew.west
matthew.west@xxxxxxxxxxxxxxxxxxxxxxxxx
http://www.informationjunction.co.uk/
http://www.matthew-west.org.uk/ (015)
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