chapter  6
32 Pages

Further Extensions for ER Diagrams with Binary Relationships

Attributes of Relationships Relationships Developing into Entities: The M:N Relationship Revisited More Entities and Relationships

More than Two Entities Adding More Attributes that Evolve into Entities

More Evolution of the Database Attributes that Evolve into Entities Recursive Relationships

Recursive Relationships and Structural Constraints Multiple Relationships The Derived or Redundant Relationships Optional Section An Alternative ER Notation for Specifying Structural Constraints on Relationships Review of the Methodology Mapping Rules for Recursive Relationships Chapter Summary Chapter 6 Exercises References Case Study

Having developed the basic ER model in Chapters 1 through 4, this chapter deals with some extensions to the basic model. In this chapter we introduce

a new concept — attributes of relationships — and give several examples of attributes of relationships. 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 refining our ER design methodology. Relationships can develop into entities, creating an intersection entity. The grammar and structured English for the intersection entity are also presented. Then, this chapter introduces the concept of recursive relationships.