a job for the query system?

I want to work with some objects like this:

Things --
[key: OID | slots: name, data]

Triples (subclass of Thing) --
[slots: beginning, middle, end]

Theories (subclass of Thing) --
pset (?) of elements: [key: name | slot: OID of some Thing]

Ian Eslick has already helped me by putting together an implementation
covering Things and Triples in a very slick way.

http://planetmath.org/~jcorneli/variant-4.lisp

In particular, the current implementation enables the user to find all
Triples which match on any particular data in the three slots. Note:
the schema is not precisely what I've listed above, which brings me to
my first question:

Question 1. What should I do to key a persistent class by its OID?

Theories have yet to be implemented. The schema is set up so that
Things to live in a Universe and Theories designate arbitrary subsets
of that Universe. The challenge that I want the data-matching
routines to work within a given Theory. This way, a Theory can be
viewed as a sub-network of the semantic net that the Universe as a
whole comprises.

I am pretty sure Ian indicated that this can be done using the up and
coming "query system". Which brings me to:

Question 2. Does this indeed look like something the query system can
handle?

Question 3. Does this look like a good set-up?

Question 3. How can I learn more about this query system and when is
it expected to be available?