Database model/design/implementation tool?

We are looking for software to assist in database design. The package would allow interactive development of a database model, entity relationships, etc.; ideally generate required SQL code for implementation; provide database model documentation (e.g. ER diagrams). Our immediate need is for something that works with Informix SE under Unix, although a program that has the flexibility to support a variety of back-end platforms would be a plus. Win95-compatible front end preferred. Suggestions from users and information from vendors are welcome. Email to pamailman@qed.com appreciated.