[sc34wg3] Subjects, role players, and user-defined association types

[Martin Bryan]

Lars Marius wrote, in response to my:

> | For example, I might want to say that a particular base name is
> | valid in English and French by using the proper XML statement
> | xml:lang="en fr". This would create two name/value assertions,
> | xml:lang<-->en and xml:lang<-->fr with the assertion type of
> | valid-in-language which the base name object would then point using
> | two basename-facet assertions. (OK, I know you are all going to say
> | I should not follow the W3C rules for defining language, and should
> | do name language specification using separate topics and
> | associations, but I'm supposed to promote the proper use of existing
> | standards before inventing new ones!)
>
> Martin, I know this is what you think, but that's not much help. The
> question is: *why* do you think this is right? *Why* should we change
> our point of view to follow you? We've spent years working to get to
> the understanding of topic maps we have now. Surely you won't expect
> us to abandon it just because you tell us it's wrong? The least you
> can do is to tell us *why* it is wrong.

The idea that facets should be discarded from the model of Topic Maps is
wrong for three main reasons:

1) Words are not bounded by languages: languages share words and therefore
the mechanism that maps topics to languages must not be identified using
scoping unless it is agreed that scope is "any" rather than "all".

2) In most topic maps I've thought through there is a need to make some
distinguishing feature that is less important than a topic, but which allows
subsetting or ordering of relevant values. This applies to continuous quanta
(such as date of publication of an occurrence) and discrete quanta (such as
security levels of occurrences or associations). Forcing these things to be
presentable scoping topics, as is the current policy of XTM users, is bad
practice for the long-term management and integration of topic maps. It may
provide a "short-term solution" to the problem, but in 5 years time it will
haunt us.

3) We should not force people to break rules in other standards. XML has a
very clearly defined and widely accepted generalized mechanism for language
identification which many applications handle using standardized modules.
These modules will work just as well if the xml:lang attribute is considered
a facet of a topic map component.

Lars Marius also wrote: "My understanding was that facets applied to
resources, not to topics."

Facets use locations that can identify to any addressable component of any
resource, including any component of a topic map.

Facets provide a generalized mechanism for associating a specific name/value
pair with a set of information resource components that has much wider
applicability than just topic maps, which is why it is perfectly permissible
in ISO 13250 to have a topic map that only contains facet definitions. You
can think of facets as the RDF of topic maps, with the facet value type
being the predicate.

Martin