Taxonomy issues

[Reagan Moore]

Anita:
You are correctly describing the situation.

One approach is to characterize semantic labels by the community that 
uses a particular definition.  This allows definitions to change in 
time and to change between communities.

A second approach is provide a "learning context" (term used in the 
education community) for each semantic label.  The "learning context" 
defines the related semantic labels and identifies relationships 
between the labels that are appropriate for a particular community. 
In the education context, a semantic label such as "sun" has a less 
sophisticated meaning when presented in the 3rd grade, than it does 
as a graduate student.  The "learning context" is a function of the 
level of sophistication of the student.

Similarly, the "learning context" for terms in astronomy depend upon 
the particular sub-discipline.  An ontology can be used to define the 
different "learning contexts" associated with the semantic labels 
used by each of the sub-disciplines, without requiring that everyone 
agree on a single exact meaning for each term.

Reagan Moore



>Thanks to Carole and Sean, I think I understand what I was trying to say
>earlier better now....
>
>
>> Of course in biology there are different classifications and
>> definitions -- there is no standard definition for what a gene is for
>> example. DAML+OIL allows multiple definitions, and will report on
>> definitions that are inconsistent. What you do then is an interesting
>> story. And it depends on what you want to use the ontology / taxonomy
>> for.
>
>It is much worse in astronomy though because no-one dies or even sues if
>we define something in ten different ways...  So I do not think the people
>constructing ontologies should have to sort out genuine inconsistencies
>(just avoid accidentally creating more ourselves!)
>
>> So, onto the subject of contradictions and inconsistency. I say that
>> all Widgets are blue, while you think that Widgets are red. So in our
>> ontology, I say:
>>
>>   Widget -> colour blue
>>
>> and you say
>>
>>   Widget -> colour red
>>
>> If we also have some constraints that say that blue and red are
>> mutually exclusive, then we have arrived at a contradiction.
>
>This implies that we should avoid mutually exclusive definitions within an
>ontology for astronomy, because people can disagree about definitions, or
>definitions can change with time.  For example, an optical astronomer
>might say that all stars with an emission line at 500 nm is a green fairy,
>and those with a line at 700 nm are red fairies.  A radio astromoner might
>then use an insensitive survey to find that only red fairies had radio
>emission and classify all radio stars as red fairies.  However if green
>fairies do have weak radio emission, some radio stars in a more sensitive
>survey could be misclassified.
>
>So, suppose a star cannot actually be both, we (as in the ontology
>authors) do not want to have to decide, and we do not want to throw out
>the information either.
>
>I suppose this is really the 'individual' case, but there are also cases
>of contradictory definitions of precisely measured properties, e.g.
>whether a red fairy is a variable star with a period of <400 days or <350
>days and a green fairy has a period of >400 or >350 days.....
>
>But I think the implications for an ontology user are the same: if I was
>searching for all the green fairies in a galaxy, I would want a warning
>about those which were classified as red and as green in radio and optical
>catalogues respectively as well as those which were classified according
>to an ambiguous definition (periods of around 375 days).
>
>What I think would be useful is if we could constrain properties to be
>"contradictory" as a description, of perhaps just as "linked", so that any
>query which involved returning a description or list of (a) green
>fairy(ies)  would automatically note any also classified as red....
>
>> One solution to this is to use the classification as a "conceptual
>> coat rack" and hang "extralogical" information off it. This is the
>> kind of thing that the RuleML initiative is aimed at. This then allows
>> us to state things about OWL classes that are not necessarily part of
>> the ontological or intensional definition of the class, but which we
>> want to make available to applications.
>
>Um, is that similar to what I am suggesting above?
>
>
>
>- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>Dr. Anita M. S. Richards, AVO Astronomer
>MERLIN/VLBI National Facility, University of Manchester,
>Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, U.K.
>tel +44 (0)1477 572683 (direct); 571321 (switchboard); 571618 (fax).