6.8: Concise Summary

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An Entity Relationship Diagram, or ER diagram, is a visual representation of a database and the interactions between its entities and attributes. The need for ER diagrams arose from the need to structure complex databases in the 1970s. Aspects of ER diagrams that are appealing include their not only being easy to understand but also easy to create and teach.

One of the earliest models was developed by Peter Chen, which included entities (rectangles), attributes (ovals) and their relationships (diamonds). Newer ER diagrams (using Unifying Modeling Language) simplify this by attaching attributes to their entities in a rectangle and by having relationships designated by lines with specific end-connection symbols that represent the following:

One-to-one
One-to-many
Many-to-one
Many-to-many

All four of the above relationships are also combined with a symbol for mandatory or optional cardinality.

There are a few naming conventions that have evolved since Chen’s original model. Entity names are typically one word, bolded, and put in the upper rectangle (the case can be interchangeable, but most use either Pascal or Camel). When keys are introduced, primary keys are camel-case and underlined, and secondary keys are just camel-case; all keys must have the same name as their corresponding entities. Attributes are camel-case, unique, and as short as possible.

ER diagrams allow a prebuild for databases which saves time, effort, and confusion for programming teams. They are also a great tool when used to help diagnose errors in the database. These simple diagrams are crucial when creating a database as efficiently and quickly as possible.