[fw-db] Complex relational dependencies with Zend_DB_TABLE

Hello,

I would like to use the zend framework api as far and mutch as possible.
Now, concernig the zend_db_table and zend_db_table_row i wonder if i can
use the depencies features at all:

- you can specify dependend tables
- you can specify a referential column map with as many columns as you want

but

- you cannot specify the operators to be used for the referntial
columns, e.g =, <>, >, < or more complex operators like SQL function,
or did I miss something?
- you cannot pass SQL expressions or/and parameters to the rules, like a
date or timestamp for comparison,
or did I miss something?
- you cannot extend the rule system by custom rules, can you?

If I am right, the only possibility to accomplish these extended rules
in ZEND_DB_TABLE relationships is to extend Zend_DB_Table and / or
Zend_DB_Table_Row with custom logic.
Am I right?

Szenario:
You want to select records of table B dependend on a parent record of
table A.
You don't have a simple FK constraint. Your RDB Model have a "valid
record" model for every record.
So you want to query only the valid records with:

is_active = true
valid_from <= timestamp (TYPE)
valid_to >= timestamp (TYPE)
parent_no = no of the parent record

timestamp must be a parameter of type timestamp, in order to be able to
query future or past dates.
"no" and not "id" is used because the rule must be bidirectional, and
for the parent record also always only the valid record should be
selected, not the unique by id!

any suggestions to get this out of zend_db_table or zend_db_table_row
with its own rule system?
if there is a rule system, i'd like to use it, instead of extending the
classes in order to built my own rule system!

thanx for any hints.