I believe that the failure to clarify that distinction and observe it consistently is the source of the disagreements.
>> On Mon, December 31, 2012 21:14, William Frank wrote:
>> ...
>> But what seems to me to be most fundamentally wrong in this
>> discussion
>> is the notion that there is a good reason to define 'kind of
>> activity' separately from 'kind of stone' or kind of hope'.
If Activity, Stone, and Hope, are categories (or classes or types) in your ontology, then you only need two metalevel terms: 'instance of' and 'subtype of' (or 'subclass of').
MW: As I explained, this does not work with a data model where you want to be able to extend your ontology in data, in particular being able to add subtypes as data instead of changing the data model by adding entity types each time you identify something new. Changing data models is expensive compared to changing data. You therefore need the entity type that the subtypes of e.g. activity would be instances of, and this is class_of_activity (or activity_type whatever your taste is).
Those terms let you talk about and distinguish instances of Activity, Stone, and Hope from subtypes of Activity, Stone, or Hope. The ontology itself should *not* have any categories with names like 'kind_of_activity' or 'class_of_activity'.
> MW: In HQDM the definition of kind_of_activity is:
>
> A class_of_activity all of whose members are of the same kind.
>
> This is not circular definition...
I agree that it's not circular. But it's not just useless, it's worse than useless because it's confusing.
It mixes the names of categories in the ontology with metalevel terms for talking about the ontology. You can simplify and clarify the ontology by getting rid of both categories: kind_of_activity and class_of_activity.
MW: No you can’t. You need to understand what the data model is trying to do, and apparently you do not.
> MW: Since class_of_activity includes arbitrary sets of activities, this
> subset is indeed significant, and includes those activities for which we
> are likely to have words, like singing, rather than mere identifiers.
If you want Singing to be a category of your ontology, all you need to say is "Singing is a type of Activity." If you want to talk about sets of categories, you need a version of logic that lets you do so. But that option does not require you to add special categories to the ontology itself.
MW: Well I wish you luck when you are working for a client and saying every time they want a new category they have to change the data model rather than adding a data record.
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Matthew West
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