Information Modeling and Relational Databases, 2nd Edition

8.6. Summary

The Entity Relationship (ER) modeling approach was originated by Peter Chen in the 1970s and allows facts to be expressed via relationships (e.g., Person was born in Country) or attributes (e.g., birthdate). Of the dozens of different ER versions in existence, the most widely used are the Barker notation and Information Engineering (IE). The popular IDEFIX approach is often referred to as a version of ER, but is actually a mixture of ER and relational approaches, with the emphasis on relational.

The Barker notation represents entity types as named, soft rectangles with a list of one or more attributes. A “*” or “•” indicates that an attribute is mandatory, and a “°” indicates that the attribute is optional. All relationships are ...