The Entity-Relationship Data Model Considered Harmful
In the world of Information Systems, the Entity-Relationship model (first defined by Chen in 1976) is widely taught and also widely used in practice. Despite the fact that the ER model is commonly considered a conceptual data model, it violates the Conceptualisation Principle as defined in the International Standards Organization report of 1982. In this paper, we will show that the ER model contains too many different ways to represent (or encode) the same proposition (or fact). Indeed, it is possible to claim that the ER model is essentially a reincarnation of the CODASYL DDL/DML model (as defined in the CODASYL DBTG report of 1971).
As the number of fact-encoding mechanisms increases, so must the complexity of any design procedure. This means that it is very difficult to provide the ER designer with effective prescriptive guidance on how to perform the design task.
The ER graphical notation is often claimed to be a good medium for communication between the users and the EDP professionals. We will show that this graphical notation does not support effective validation procedures that involve the user (the only person who truly knows the semantics of the application).
KeywordsDesign Procedure Conceptual Schema Uniqueness Constraint Cardinality Constraint Informal Part
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