ABSTRACT
Having developed the basic entity relationship (ER) model in Chapters 4 through 7, this chapter deals with some extensions to the basic model. In this chapter, we introduce a new concept-attributes of relationships; we present several examples. We then revisit step 6 of the ER design methodology to include attributes of relationships. Next, the chapter looks at how more entities and relationships are added to the ER model and how attributes and relationships evolve into entities, all the while re›ning our ER design methodology. Relationships may develop into entities, creating an intersection entity. ”e grammar and structured English for the intersection entity are also presented. ”en, this chapter introduces the concept of recursive relationships.
