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Speaking ERDish and Drawing Relationships

This tutorial discusses how to describe a relationship using precise language, and in turn, correctly draw the relationship.

Objectives

This tutorial covers the following objectives:

  • State database relationships between entities in precise words (ERDish)
  • Draw entity relationship diagrams.
  • Draw and label relationships correctly on an ERD

Purpose

  • Most businesses use industry-specific terminology (words which have a special meaning within that business) in order to communicate information.
  • Data modeling uses industry-specific terminology as well, which we will call ERDish for the purposes of this class.
  • ERDish—the vocabulary used to clearly communicate the business rules that are captured on an ERD—will give you a common language both when collecting the business rules from your client and communicating them to the Database Administrators who will implement your design.

ERD Language

  • ERDish is the language we use to state relationships between entities in an ERD.
  • You have already been speaking and writing it, when you identified relationships and specified optionality and cardinality.
  • We are simply breaking down each ERDish sentence into its components.
ERD Language

The Components of ERDish

  • EACH
  • Entity A
  • OPTIONALITY (must be/may be)
  • RELATIONSHIP NAME
  • CARDINALITY (one and only one/one or more)
  • Entity B
  • Since each relationship has two sides, we read the first relationship from left to right (or top to bottom, depending on the ERD layout).
Draw entity relationship diagram
  • Now we read the relationship from right to left.
The relationship from right to left.

It is often necessary to add a small “s” to the end of the second entity name to make the ERDish sentence more readable.

  • Now bring it all together.
Bring ERD all together.
  • Each EMPLOYEE must work in one and only one DEPARTMENT.
  • EACH DEPARTMENT may be responsible for one of more EMPLOYEEs.

There are lots of tools that allow to draw entity relationship diagram, one of the most recommended one to use is Lucidchart.

Terminology

Key terms used in this tutorial included:

  • ERDish

Summary

In this tutorial, you should have learned how to:

  • State relationships between entities in precise words (ERDish)
  • Draw entity relationship diagram
  • Draw and label relationships correctly on an ERD

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