面向对象系 统分析与设计 第七章.ppt

Chapter 7:Conceptual Data Modeling Object-Oriented Systems Analysis and Design Joey F. George, Dinesh Batra, Joseph S. Valacich, Jeffrey A. Hoffer Chapter Objectives After studying this chapter you should be able to: Determine how to develop conceptual data models from use cases. Understand UML notations for conceptual data modeling. Explain relationship characteristics such as degree and multiplicity. Chapter Objectives (Continued) After studying this chapter you should be able to: Describe data relationships such as association, aggregation, and generalization. Describe different kinds of attributes such as identifier, multivalued, and derived. What Is a Conceptual Data Model? A detailed model that shows the overall structure of organizational data; it is independent of any database management system or other implementation considerations. Represented by UML class diagrams Conceptual Data Model Elements Classes Attributes Identifiers Associations, aggregations, compositions Generalizations Time dimensions Integrity rules Security controls What Is an Object? An entity that encapsulates data and behavior Examples: product, employee, order, line item Class – a set of objects that share the same attributes, operations, relationships, and semantics (abstract) Instance – a single object (concrete) What is an Attribute? A named property of a class that describes a range of values that instances of the attribute may hold Types of Attributes Simple attributes – contain single data item Identifiers – connect unique key value Multivalued attributes – contain multiple values simultaneously Composite attributes – group of related attributes Stereotypes in Class Diagrams Stereotype – a construct that extends the UML vocabulary Identifier stereotype PK for primary key Multivalued stereotype multivalued Identifiers and Keys Identifier – an attribute or combination of attributes that is selected as the unique characteristic for a class Candidate key – an att