1. OBJECT-ORIENTED DBMS

2. Structured & Object Oriented Approaches Structured approach – long history, well- documented  ERD - modeling data  DFD - modeling process  Tools – System Architect, Visible Analysis OO approach – new, offer benefits such as soft reuse  Class Diagram - modeling data  USE-Case diagram - system functionalities  Tools – Rational Rose

3. OO Concepts Classes  Class is a group of objects that have similar attributes (properties) and behavior  All objects in class have similar attributes and they perform similar operations  E.g. all pupils in a students class will have the same attributes (not attribute values) such as name and address.

4. An object is a structure that encapsulates (or packages) both data and methods.  The data (also called properties) describes the attributes of the object while methods (also called operations, services, functions or procedures) describe its behavior.

5. An Object with Attributes and Methods Employee EmpNo EmpName Pay ModifyInfo ComputePay Object’s Name Object’s Attribute Object’s Method

6. Encapsulation Encapsulation means packaging both the data object’s and method together Only methods within an object are allowed to modify the object’s attribute (data). The data and details of the methods of an object are hidden from other object’s data and methods – i.e. the external methods (belonging to other objects) cannot modify other object’s attribute.

7. Class Hierarchy Person StudentLecturer Superclass (also known as base, parent or ancestor class) Subclass (also known as child or derived class)

8. Multilevel Class Hierarchy Person EmployeeStudent Foreign employee Local employee Part Time Student Full Time student Superclass Base class

9. Inheritance Inheritance is the property that when classes are arranged in a hierarchy, a derived class can inherit (automatically) the properties ( attributes) and behaviors (methods) of its parent or base class.

10. e.g. ClassAttributesMethods PersonName, Age, sexInitialize, Add, Modify StudentStudNo, CourseChangeInfo EmployeeEmpNo, PayComputePay

11. Inherited attributes and methods Person Name Age Sex Initialize Add modify Employee EmpNo Pay ComputePay Student StudNo Course ChangeInfo Derived Properties Name Age Sex Initialize Add modify

12. OO Databases In OO data management (OODM), each object in the system has an identity that is internal to the data stored within the object There is no concept of primary key OODBMS maintains an external identifier for each object, which is not accessible to any object, function or application The identity of the object does not change

13. Types of Methods TypesDescription Occur MethodsThese methods provide basic maintenance functions for class instances and classification structure. There are 4 Occur Methods: Add – add instance of object Change – change the property of the object’s instances Delete – delete an object’s instances Select – Select an object Calculate Methods Perform calculation on data within an object (can be simple or complex) Monitor Methods Used to monitor system’s characteristics such as when the stock level of a product reaches a specified value.

14. Advantages of OODBMS Enriched modeling capabilities – closely model the real world object Extensibility – allows to develop new abstract data types using existing data types More expressive query Suitable for advance DB applications

15. Disadvantages of OODBMS Lack of experience Lack of standards Lack of view mechanism Inadequate security

16. Despite of its capability, OODBMS did not gain so much popularity and not widely accepted. Reasons why organizations are reluctant to use OODBMS :  Existing investment  High switching cost  Using two methodologies in the same organization can be expensive  Staff training cost

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