Database designers begin the logical design stage by converting business objects and their characteristics into entities and attributes. They plug both entities and attributes into an ER diagram as the first step in designing a conceptual model.
Keep in mind that a conceptual model does not contain any data; rather, it illustrates the structures of a database, the architecture of the data container. Think of building a house: you build the house before you place any furniture inside. But don’t carry this analogy too far: when you design a database, you build a house to fit the furniture you already have rather than buying furniture to fit the house.

After completing this module, you will be able to:

1. Define entities and entity attributes
2. Explain the purpose of entity identifiers
3. List rules for creating entity identifiers
4. Describe instances of entities
5. Describe attribute domains and domain types
6. Explain the problem with multi-valued attributes
7. Describe how to resolve multi-valued attributes by adding more attributes
8. Describe how to resolve multi-valued attributes by creating a new entity
9. List entity and attribute constraints

The next lesson describes entities and their attributes.