We have yet to learn many of the details of the E/R model, but we have enough to begin study of very important issue of what forms a good design and what should be avoided. In

Careless selection of a relational database schema can lead to problems. For instance, Example (b) of "Combining Relations" showed what happens if we try to combine the relation for a many-many relationship with the relation for one of its entity sets. The major problem we