Criteria is a module for abstracting queries to various data sets.
For instance, you might have a flat text file, or an array of Ruby
objects, or a SQL database, and wish to perform the same query on any
given source, without different versions of code for each.  Here's a
quick example (more on the site):

idx1 = SQLTable.new("orders")
q1 = (idx1.price > idx1.paid) & (idx1.duedate < Time.now.to_i)

puts q1.select

# => SELECT * FROM orders WHERE ((orders.price > orders.paid) AND
# (orders.duedate < 1062616643))

Author:	Ryan Pavlik <rpav@mephle.com>
WWW:	http://mephle.org/Criteria/