The relationship tab in Manage Database is not an ERD (Entity-Relationship Diagram). Sometimes it looks a lot like an ERD but it is so much more. An ERD represents the structure of your solution while the relationship graph contains structure as well as what I like to call techniques. Techniques are relationships that allow a feature to function properly, not provide structural integrity. You might create a filtered portal as an interface option or use a multi-key relationship and a script to drill down through records to create found sets or even a conditional popup menu that requires a non-structural relationship to operate. With a discussion of anchor-buoy relational design as the main thrust, this article attempts to impart a better understanding of relationships.