tailieunhanh - Lecture Database Systems - Lecture 25
After completing this chapter, students will be able to: Computer organization, data representation, integer arithmetic, binary representation, floating point representation, machine instruction characteristics, instruction cycles, types of operands, pentium and power PC data types, microporessor bus structure, address, data. | CSC271 Database Systems Lecture # 25 Summary: Previous Lecture Structural constraints Multiplicity Cardinality Participation Connection traps Fan traps Chasm traps Enhanced Entity-Relationship Modeling Chapter 12 Enhanced Entity-Relationship Model Since 1980s there has been an increase in emergence of new database applications with more demanding requirements Basic concepts of ER modeling are not sufficient to represent requirements of newer, more complex applications Response is development of additional ‘semantic’ modeling concepts Enhanced Entity-Relationship Model The ER model supported with additional semantic concepts is called the Enhanced Entity–Relationship (EER) model Examples of additional concepts of the EER model, namely specialization/generalization, aggregation, and composition Specialization/Generalization Superclass An entity type that includes one or more distinct subgroupings of its occurrences, which require to be represented in a data model Subclass A distinct subgrouping of occurrences of an entity type, which require to be represented in a data model For example, the Staff superclass may have subclasses as Manager, SalesPersonnel, and Secretary etc. Specialization/Generalization Each member of a subclass is also a member of the superclass In other words, the entity in the subclass is the same entity in the superclass, but has a distinct role . Manager/Supervisor is also a Staff etc. The relationship between a superclass and a subclass is one-to-one (1:1) and is called a superclass/subclass relationship Specialization/Generalization Some superclasses may contain overlapping subclasses, . a member of staff who is both a Manager and a member of Sales Personnel Not every member of a superclass need be a member of a subclass, . members of staff without a distinct job role such as a Manager or a member of Sales Personnel Specialization/Generalization Superclasses and subclasses are used to avoid describing different types of staff | CSC271 Database Systems Lecture # 25 Summary: Previous Lecture Structural constraints Multiplicity Cardinality Participation Connection traps Fan traps Chasm traps Enhanced Entity-Relationship Modeling Chapter 12 Enhanced Entity-Relationship Model Since 1980s there has been an increase in emergence of new database applications with more demanding requirements Basic concepts of ER modeling are not sufficient to represent requirements of newer, more complex applications Response is development of additional ‘semantic’ modeling concepts Enhanced Entity-Relationship Model The ER model supported with additional semantic concepts is called the Enhanced Entity–Relationship (EER) model Examples of additional concepts of the EER model, namely specialization/generalization, aggregation, and composition Specialization/Generalization Superclass An entity type that includes one or more distinct subgroupings of its occurrences, which require to be represented in a data model Subclass A distinct .
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