[Voevent-core] Fwd: standard vocabulary

[Doug Tody]

It appears that both VO-Event and DAL have similar requirements for a
standard nomenclature for object classification, e.g.,

     process.variation.burst;em.gamma
     process.variation.burst;em.X-ray

and so forth as has been suggested.  We had a similar discussion in
DAL a while back but I will summarize the conclusions again here.

In DAL (and probably VO-Event as well) this comes up in two different
areas, object description via query response metadata, and in the
query itself.

For object description in the query response one wants as precise a
description of the object classification as is known.  Long descriptive
UCD-like descriptions as in the examples above are fine.

For a query it is important that a more coarse-grained classification
be possible, which allows a single string to potentially match many
fine-grained type classifiers.  For example, "star" could match many
object types.  It would be good if these coarse-grained classifier
names could be brief for use in a query, as they will probably pass
through to the service unchanged, originating from a human user or
client application.  The relationships between the coarse-grained
names and the detailed classifications could be one-to-many and
possibly hierarchical as well.

It would be good to avoid the use of special metacharacters in these
names.  For example, in our earlier discussions, "*" was used as a
shorthand for "star" in the naming convention proposed, but this could
cause problems for software, for example if pattern-matching is used.

We will need to standardize both detailed object classification and
query input, so it is important to address both of these areas in
whatever scheme we come up with.  One way to ensure that this happens
might be to implement an "object resolver" service or web page to
map short names to lists of classifiers once a list of detailed
classifications becomes available.   - Doug