The Entity-Relationship Model

Abstract

In the remaining chapters, we discuss the extended entity-relationship model, the higher-order entity-relationship model HERM. However, in order to understand why it is necessary to extend the model, we will briefly discuss the original ER model first published by Chen [Che76]. It has been extended or restricted by several authors. The number of extensions can be estimated to be more than 80. Further, the model has been used with different semantics and different intentions. The graphical notation has been stable. Some of the restrictions, such as the limitation to binary relationship types or the limitation to 1-n-binary relationship types (functions), led to frightening modeling. Extensions of the model can be safe or unsafe. In Sect. 4 we show how to extend the original ER model to a safe, well-founded and practicable ER model. Due to the problems with pointer or reference semantics we only use set semantics.

I hear your message, but I have no faith; The miracle is faith’s most treasured child, But I dare not reach for these high regions, The source and music of glad tidings. And yet, accustomed to these harmonies from childhood, I now can hear their summons to return to life.

Goethe, Faust I, Night