Data model diagramming tool similar to Core Data modeler

I need a simple data model diagram tool written in Cocoa/Objective C. To get an idea of what the final product should look like, look at the core data data modeling tool in Xcode. Please refer to Xcode Tools for Core Data ([login to view URL]) wherever page numbers are mentioned below. Appearance --------- It needs to look similar to the image on page 11, with the following exceptions: 1. In the browser pane (page 15), I only need an Entities table and a Properties table. a. The Entities table only needs one column, for entity name. b. The Properties table needs three columns. One for property name, one to indicate whether the property is an attribute or a relationship, and one for the (Entity) target of a relationship. 2. Though I do need add and delete buttons in the browser pane (for entities and properties tables), none of the other bells and whistles are needed. 3. Diagram elements must look precisely like the diagram elements on pages 23 and 26, except that we only need unidirectional arrows. Behavior ------- 1. Roll-up and Expansion (page 26). Double-clicking a node's "title bar" should toggle between rolled up and expanded view. 2. Entity nodes should be capable of being moved with the mouse, anywhere in the diagram view. 3. Relationship lines should update appropriately whenever an entity node is moved, rolled up or expanded. And that's pretty much it. I don't need to load or save the models. I just want to be able to: 1. Create, delete and rename entities. 2. Create and delete attributes and one-way relations. 3. Move diagram elements around in the diagram view. If it turns out to be *very* easy and quick to do it, it would be nice if I could have a way to save the diagram to pdf -- but I'm happy if I can just get a screenshot from the tool I've just described. Deliverables ---------- I need a complete Xcode project that I can modify or rebuild myself. The diagram elements must be expressed in code (not interface builder), though I expect interface builder to be used elsewhere.