Segment building tool

This awesome startup I'm working for is putting together APIs to do instant event-driven marketing. What? Segmentation, boolean algebra. Still what?
Essentially the problem we are trying to solve with this quick prototype is how to build a condition (boolean algebra) to extract a segment of users from a database. This is a particularly painful problem for companies with massive database of users (b/millions). This is iteration 1, next week we're testing with more users and go to iteration 2. Exciting times!