questions about varlist and Query

Fellow hacker,

I am new comer to postgres development community. Currently, I am
implementing tightly coupled machine classifiers within postgres. The
grammer looks like Train Parameter_list (class1,class2,class3...). I have
two major problems right now.

1. Train is a statement and it is suppose to return some parameters in the
form of a query. (To be used by a classifier later.) How can I return a
Query with self specified column name and data vectors?

2. class1, class2 are all supposed to be relations/query result. But what is
a proper container to hold them. I found var_list to be a good candidate as
it can contain unconstrained number of var_values. But var_values are of
constant types. Can I just add query as a constant? Anyone had this kind of
implementing experience?

Thanks,
John