ASA SQL User's Guide
Designing Your Database
In designing a database, you plan what things you want to store information about, and what information you will keep about each one. You also determine how these things are related. In the common language of database design, what you are creating during this step is a conceptual database model.
The distinguishable objects or things that you want to store information about are called entities. The associations between them are called relationships. In the language of database description, you can think of entities as nouns and relationships as verbs.
Conceptual models are useful because they make a clean distinction between the entities and relationships. These models hide the details involved in implementing a design in any particular database-management system. They allow you to focus on fundamental database structure. Hence, they also form a common language for the discussion of database design.
The main component of a conceptual database model is a diagram that shows the entities and relationships. This diagram is commonly called an entity-relationship diagram. In consequence, many people use the name entity-relationship modeling to refer to the task of creating a conceptual database model.
Conceptual database design is a top-down design method. There are now sophisticated tools such as Sybase PowerDesigner that help you pursue this method, or other approaches. This chapter is an introductory chapter only, but it does contain enough information for the design of straightforward databases.
Entities
Relationships
Changing many-to-many relationships into entities