[sc34wg3] Disentangling 'scope', 'context' and 'applies'

[Martin Bryan]

Just a few (carefully edited) reminders from the definition of scope in
13250:

Scope
The extent of the validity of a topic characteristic assignment:
the context in which a name or an occurrence is assigned to a given topic;
the context in which topics are related through associations.
The specification consists of a set of topics which ... are called themes
A given scope is the union of the subjects of the set of themes
Note 3: If it is desired to specify a scope which is the intersection of two
topics this can be accomplished by creating a topic whose subject is that
intersection.

Also note the first definition of facet: The subset of information objects
that share an externally applied property.

When 13250 was being defined things like language and dates were seen as
being likely to be defined as facets rather than scopes as they are
typically externally defined. (They typically affect the view users have of
the data, rather than the underlying topic set in most, though not all,
cases.) Scope was needed to allow for the fact that the same name might be
used in more than one domain, or for the fact that specific occurrences or
associations might be domain specific. By adding themes to complete topic
maps you could also prevent unintended merging of topics through the
application of "constraining topics" (my terminology).

Marc uses the term Perspective for "the way a user wishes to look at a Topic
Map", and then equates this to "the set of themes which apply". To me this
against the spirit of 13250 in the sense that it seems to require all
controls of the subsetting of topic maps to be defined formally as topics
and applied formally as scopes.  This does not seem to allow sufficient
power to concepts such as roles, which are equally applicable to managing
"the way a user wishes to look at a Topic Map".

What I originally expected scope to be used for was queries of the form
"Show me the set of names/occurrences that are relevant ONLY when domain (x)
is the applicable scope". If I want to restrict my query further I could say
"Show me the set of names/occurrences that are relevant ONLY when BOTH
domain (x) and domain (y) are specified as applicable scopes". Each scope
would be an individual subsetting operation. Multiple scopes can be applied
sequentially to further subset the list of returned objects. The effect of
using multiple domains within the query will be the intersection of the two
queries, but the scopes do not all have to be applied in a single query,
individual scopes identifying individual subsets of the topic
name/occurrence/association set.

Martin Bryan