Entity class

When Dr. Chen developed entity/relationship modeling [1] (commonly known as data modeling), he used the term "entity type" to define the boxes on his diagrams as representing classes of things. For example "Person" would be an entity type, and "Sally Jones" would be an "entity" or an "instance" of the entity type. Over the years, however, practitioners became sloppy, and the term "entity" came to refer to the class of things.

Then the object-oriented community came to the fore with its use of the terms "class" and "object", where object was clearly an instance of a class. In their criticism of the entity/relationship community, they claimed that the object-oriented approach more correctly represented the concept of class.

This of course was mistaken, because data modelers have always been clear on the distinction between the definition of a class of things and instances of those things. The problem was sloppy usage.

In the interest of clarity of language, therefore, the term entity class will henceforth be defined as the definition of a kind of thing of significance to an organization. Conceptual data models will thus be composed of entity classes, attributes, and the relationships between pairs of entity classes.

References

1. Chen, P. 1976. “The Entity-Relationship Approach to Logical Data Base Design”. The Q.E.D. Monograph Series: Data Management. Wellesley, MA: Q.E.D. Information Sciences, Inc. This is based on his articles, “The Entity-Relationship Model: Towards a Unified View of Data”, ACM Transactions on Database Systems, Vol. 1, No 1, (March 1976), pages 9-36.yes