Dear Doug and William, (01)
> 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'.
>
> >From the discussion, "kind of activity" is far narrower than "subset
> of
> activity". I would prefer a clearer description of its meaning than
> was
> given. The given gloss:
> "*kind of activity* means a characterization that is true of some
> activities, so distinguishing these activities from all other
> activities" (02)
MW: I am not sure where this comes from. In HQDM the definition of
kind_of_activity is: (03)
A class_of_activity all of whose members are of the same kind. (04)
This is not circular definition, because kind_of_activity is just a label -
you can substitute X, or A without changing anything, whereas "kind" in the
definition is an English word. The appropriate usage for "kind" from the OED
is: (05)
A class of individuals or objects distinguished by attributes possessed in
common; a genus or species; (06)
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. (07)
> does not restrict the type of characterization, and without a
> meaningful restriction on the type of characterization, i agree that
> there is little reason to define a "kind of activity" (with an
> exception noted in two paragraphs below). (08)
MW: It is not intended to, merely to distinguish from arbitrary sets, which
I also a requirement.
>
> However if the types of characterizations intended are semantically
> restricted the concept could be useful. In addition, if instances of
> "kind of activity" are required to be disjoint with each other or
> arranged in a tree with disjoint limbs, and/or if subtypes of an
> instance of "kind of activity" may not themselves be instances of "kind
> of activity", such a concept could be useful. (09)
MW: They are not required to be disjoint, and since kind_of_activity is a
subtype of class_of_activity, it is necessarily the case that any instance
of kind_of_activity is an instance of class_of_activity.
>
> I haven't looked at the ontology, but i find it likely that "kind of
> activity" was defined so as to enable properties (and maybe rules) with
> arguments restricted to its instances. (010)
MW: That is correct. (011)
> If such properties/rules would
> be applicable to any subset of "activity", then "kind of activity"
> could still be useful if the language allowed rules to have clauses
> specifying that "X is an instance of *kind of activity*" but not "X is
> a subtype of *activity*". (012)
MW: All instances of kind_of_activity are necessarily subtypes of activity.
Kind_of_activity is a subset of class_of_activity, and class_of_activity is
the powerset of activity, i.e. the set of all subsets of activity. So
necessarily instances of kind_of_activity are subtypes of activity. Indeed
it is the purpose of this construct to enable these to be held as data,
rather than in the data model. (013)
Regards (014)
Matthew West
Information Junction
Tel: +44 1489 880185
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http://www.matthew-west.org.uk/ (015)
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