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Entities and relationships

All data models must represent the relationships that exist between entities. The practical question for us is how to do that using a relational database. Using columns to represent the attributes of a particular type of entity is an easy step, but relationships exist outside an entity: how then can we used the basic structures available to represent relationships as well?

This set of notes covers probably the single most important topic in the module. Without a good understanding of the concepts discussed here, you will not be able to use or develop databases with confidence. Once you do understand how relationships are represented, you will be able to handle all of the other topics more easily.