There's a module for that!

Originally published at OpenCraft

Using the CCK + Views platform, we can replicate the traditional ER (Entity-Relationship) framework into a rapid application development environment that minimizes procedural and SQL programming by replacing most of it with "Visual ER programming": a way to specify data model and behaviour in terms of SQL-like abstractions directly inside the runtime Drupal environment - and reaping the benefits of incremental, always functional output.

ER Modeling

ER modeling deals with defining entities and relations among them.