> Dear William,
>
>
>
>
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).
>
> So,
perhaps defining class_of_activity as a special kind of class *is*
> peculiar, but useful, as a way to get run-time subclasses in a
relational
> database.
>
>
>
>
MW: I don't see why it should be considered peculiar. There is nothing
> strange or peculiar about powersets. The only question is whether
they are
> useful in a particular context.
>
> (01)
> Perhaps I was misunderstanding your models as intended to be
optimal for
> understand and formalizing the ontology of a domain
of human endeavor,
> while instead they are intended to optimally
support that understanding in
> a
> way that can be used
in a given kind of technology. A way to avoid the
> 'impedence
mismatch' between classes or E/R entity types and relational
>
tables.
>
>
>
> MW: You are essentially
correct, but I would put it slightly differently.
> For me there
is an underlying ontology that includes the subtypes both
>
directly and within the powerset, and depending on the implementation
> technology different parts come to the fore. For example, there is
an OWL
> version of ISO 15926 that just uses the subtypes.
Different implementation
> technologies have different limitations
that you have to live within.
>
> As below:
>
> 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.
>
>
> This is indeed a problem, I can
see how this might be a very good
> solution.
> I think
there is more than one solution to it.
>
>
>
> MW: There usually is, but the growing emphasis on Master and
Reference
> Data
> Management, which generally follows
this approach, suggests widespread
> adoption.
>
>
>
> Regards
>
>
>
> Matthew West
>
> Information Junction
> (02)
> Tel: +44 1489 880185
>
> Mobile: +44 750
3385279
>
> Skype: dr.matthew.west
>
>
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