PMTM4 templates vs. TMCL (was: Re: [topicmaps-comment] RE: OASIS vsW3C)

["Steven R. Newcomb" <srn@coolheads.com>]

Let me take this opportunity to explain the relationship between
association templates in PMTM4 and TMCL.  In my view, far from being
mutually adverse in any way, PMTM4 and TMCL need each other.

PMTM4 merely explains how sets of constraints -- constraints that
might be expressed in TMCL -- actually participate in the Topic Map as
topics.

The constraints that will be established by TMCL expressions will also
be reifiable as topics.  One of the purposes of PMTM4 is to show how
those topics are always findable in the topic map from the perspective
of the assertions that are constrained by them.  Surely this is a good
and necessary thing (see final paragraph below).

Neither the Topic Maps paradigm nor PMTM4 constrain how the subjects
of topics can be expressed ("indicated").  TMCL is going to be a
perfectly good way of expressing such subjects, and, I hope, better
than most.

I would be deeply disappointed in the outcome of the TM
standardization process if we abandoned one of the cardinal
requirements that has always driven the design of TMs.  That
requirement is that any subject that affects the meaning of a topic
map must be reified as a topic in that same topic map.  This is the
reason why

* association templates (association classes) are topics,

* associations are topics (i.e., they are topics in that they 
                    can be role players and scope components),

* association roles (role classes) are topics,

* scope components are topics, and

* recognized player of role classes are topics  <<-- this is the one
                                                  we're talking about.

Subjects that participate in some topic map in any special way must
always be reified as topics, just like any subject.  The "specialness"
of the participation of such topics must be rigorously accounted for
in the model of what topic maps mean.  We must resist the temptation
to privilege any subjects in such a way that they somehow participate
in a topic map, but, at the same time, they're not *in* the topic map.

* Knowledge is knowledge.  Either it's there, or it isn't.

* Either topic maps are self-describing, or they aren't.

* Either all subjects are reified as topics, or they aren't.

We can't afford to create a situation in which the constraints that
govern some class of association aren't required to be reified as
topics, or in which such topics aren't findable in some rigorous,
predictable way.  PMTM4 proposes such a rigorous, predictable way.  In
any case, even leaving PMTM4 aside for the moment, the specification
of how the role-player constraint topics are connected to the
associations that they constrain is quite orthogonal to the issue of
how those constraints are expressed (e.g., in TMCL).

-Steve

--
Steven R. Newcomb, Consultant
srn@coolheads.com

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