The Objects Model and the Class Diagram

The Objects Model and the Class Diagram

Peretz Shoval (Ben-Gurion University, Israel)
DOI: 10.4018/978-1-59904-201-5.ch002
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Abstract

The objects model (or object oriented [OO] model) is a conceptual-application model that is used to define a database schema representing a certain reality. The model views the world as consisting of objects belonging to classes. The objects of these classes have attributes, behavior (i.e., functions), and various relationships with other objects. The objects model can be presented as a class diagram (also termed OO diagram or objects diagram). Like an entity relationship diagram (ERD), the class diagram has two main goals: 1. To serve as a communication medium between the developers (analysts/ designers) and the users or their representatives. The diagram is created as a result of the interactions between the two parties, during which they discover and define the users’ information needs; the diagram serves like a contract between these two sides which summarizes the users’ needs. 2. To be the basis for further development of the information system (IS). Based on the diagram, it should be possible to design the database schema of the application, and (partially) the functions that it will have to perform. For that, it is necessary to transform the class diagram into an equivalent verbal description—an objects schema. This is done using an object definition language (ODL), similar to data definition language (DDL) in the relational model. In principle, all components of the class diagram are mapped to the objects schema. However, the objects schema includes more details which are not included in the diagram. For example, in the diagram each attribute has a name, and some attributes may have specific constraint definitions (e.g., key, unique); in the objects schema there are more detailed definitions, including the attributes’ domains or data types (e.g., numeric, char., real, etc.) and lengths. Another example, in the class diagram, we only write the names of the classes’ functions, while in the objects schema we specify the parameters of the functions. As aforementioned, there is a great deal of similarity between the OO and ER models and diagrams, since the ER model is one of the sources from which the objects model originated. But there are differences between the two models, which we will review later on. One of these differences is that the ER model is “static,” that is, it only deals with the data structure, while the objects model also includes “behavior,” that is, the functions that operate on the data. The rest of this chapter is dedicated to describing the components of the objects model and the class diagram. The description is organized in four main categories: objects and classes, attributes, relationships, and functions.

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Table of Contents
Acknowledgments
Peretz Shoval
Chapter 1
Peretz Shoval
The term “object oriented” spread in the last decade and a half, throughout many fields of computing, including the analysis and design of... Sample PDF
Introduction to the Objects Approach in Software
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Chapter 2
Peretz Shoval
The objects model (or object oriented [OO] model) is a conceptual-application model that is used to define a database schema representing a certain... Sample PDF
The Objects Model and the Class Diagram
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Chapter 3
Peretz Shoval
This chapter discusses considerations and rules for identifying classes, attributes, relationships, and functions; and presents case study examples... Sample PDF
Creating Class Diagrams
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Chapter 4
Peretz Shoval
This chapter first explains why it might be preferred to first create an entity relationship diagram (ERD) and then map it to a class diagram. The... Sample PDF
Mapping Entity Relationship Diagrams in Class Diagrams
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Chapter 5
Peretz Shoval
This chapter first explains the need to map a class diagram to a relational schema. Then, most of the chapter is dedicated to presenting and... Sample PDF
Mapping Class Diagrams to Relational Schemas
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Chapter 6
Peretz Shoval
This chapter reviews the evolution of object oriented (OO) methodologies and unified modeling language (UML). Most of the chapter is dedicated to... Sample PDF
Object Oriented Methodologies and the UMI
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Chapter 7
Peretz Shoval
This chapter starts with a brief discussion on approaches to system development methodologies and the motivation for the development of the... Sample PDF
Combining the Functional and Object Oriented Approaches: Intro to FOOM
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Chapter 8
Peretz Shoval
This chapter elaborates on the activities and products of the analysis stage with functional and object oriented methodology (FOOM). The products of... Sample PDF
Information Systems Analysis with FOOM
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Chapter 9
Data Dictionary  (pages 230-247)
Peretz Shoval
This chapter explains the roles of a data dictionary (DD) in the development of the information system (IS) and describes its components. The... Sample PDF
Data Dictionary
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Chapter 10
Peretz Shoval
This chapter starts with an overview of the design phase according to the functional and object oriented methodology (FOOM) and presents the... Sample PDF
Transactions and TheirTop-Level Design
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Chapter 11
Peretz Shoval
This chapter deals with the design of the interfaces between the users and the system. First, it describes a method for the design of menus... Sample PDF
Design of the Man-Machine Interface: Menus, Inputs, and Outputs
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Chapter 12
Peretz Shoval
This chapter describes how to map a top-level description of a transaction into a detailed description, and then how to “decompose” a detailed... Sample PDF
Detailed Design of the Transactions and Class Methods
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About the Author