Self Review Questions Theoretical Background

1.3 Self Review Questions

1. What do you understand about relational data model? 2. There are two methods to design a relational data model. Define both methods. 3. What are the basic components of ERD? 4. How mapping from conceptual design to logical design can be performed? 5. What are the differences between Entity-relationship data model and object- based data model? 7 2 Introduction Object-based data model is a generic data model, which is applicable to all types of information content. It is one of the approaches that can be used in order to develop a conceptual data model for any database application. In fact, there are some variations in the notations for object-based data model. However, in this practical, students will use the notations, which are suggested in the textbook ROB, P AND CORONEL, C., 2004. Database Systems : Design, Implementation Management. Although the notation is simple and straightforward, it covers all the essential parts of object-based modeling techniques. At this stage, the intention is to introduce the basic concept of object-based data modeling and to show how object-oriented concepts have influenced data model. The objectives of this practical include: To describe the essentials of the object-based modelling method To develop conceptual design using Object-based approach To define business rules for relationship between objects To identify participation constraints in relationship To identify superclasssubclass for objects To develop object space diagram 8

2.1 Theoretical Background

Students will be given the opportunity to learn how to develop database conceptual design using UML Unified Modeling Language in subsequent chapters. UML has been accepted as a standard to graphically model a system and it has been widely used for object-oriented system design. Students are required to develop a conceptual design using object-based approach. There are a few assumptions that students need to know before attempting to develop object-based data model. These include: i. All database requirements for the system has been collected. ii. Conceptual design for the system was initially has been developed using ER approach. iii. Conceptual design has been mapped to relational data modellogical design. iv. The logical design has been implemented and the tables have been populated with some data. 9 Table 2-1 below presents a comprehensive comparison of features between three types of data models. Table 2-1 : A Comparison of Object-based data model, ER data model, and Relational Model Features Conceptual Design Logical Design Object-based Data Model ER data model Relational Model Type Entity definition limited Table definition limited Object Entity Table row or tuple Class Entity set Table Instance variable Attribute Column attribute OID NA NA NA Primary key Primary key Object schema ER diagram Relational schema Class hierarchy NA NA Inheritance NA NA Encapsulation NA NA Method NA NA 10

2.2 Exercise