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Data Modeling Made Simple: A Practical Guide for Business and IT Professionals by Steve Hoberman

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CHAPTER 6 What are relationships?

Rules all around usRelationships tell the taleConnecting the dots

This chapter defines rules and relationships and the three different levels at which relationships can exist: conceptual, logical, and physical. Data rules are distinguished from action rules. Cardinality and labels are explained so that you can read any data model as easily as reading a book. Other types of relationships, such as recursive relationships and subtyping, are also discussed.

Relationship Explained

In its most general sense, a rule is an instruction about how to behave in a specific situation. The following are examples of rules that you are familiar with:

  • Your room must be cleaned before you can go outside and play.
  • If you get three ...

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