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8.Discuss the main problems of distributed databases. 9.List and explain any fiveadvantages of a distributed database management system. 10.With help of illustrative diagram, main discuss three architectures of parallel DBMS
99 Week Nine Object-Oriented Database Systems Objectives 1)The Object-Oriented Paradigm 2)Basic Definitions and Features of OODBS 3)The Object-Oriented Database System Manifesto 4)Examples of Object-Oriented DBMS “Old” Database Applications: Featuresi.Uniformity ii.Record orientation iii.Small data items iv.Atomic fields v.Short transactions vi.Static conceptual schemes Who Needs Object-Oriented Databases? i.Computer-aided design (CAD) ii.Computer-aided software engineering (CASE) iii.Multimedia databases iv.Office information systems (OIS) v.Expert database systems Conventional DBMS for New Applications: Disadvantages a)Artificial representation of complex structured objects. b)Properties of objects cannot be modeled in an appropriate way c)Operational semantics of complex structured objects is not expressible d)Different levels of abstraction are not supported e)Lack of trigger, constraint and event mechanisms f)Clumsy database access (impedance mismatch) Object-Oriented Paradigm Our environment exclusively consists of objects. Together with the objects comes their behavior; i.e. objects are described by their functionality Mostly we know the functionality of objects but we don't know how this functionality is realized (encapsulation) Objects react to messages. Only the objects themselves decide in which way they react to a message. Different objects may react to the same message in different ways (polymorphism) Objects inherit characteristics and abilities as a result of their membership of a special class or category
100 The concepts of inheritance and polymorphism can best be exploited if the underlying system supports run-time type checking and late binding - the operation to be used is chosen at run time and converted to a program address Object-Oriented Databases: Basic Definitions In an object-oriented system everything is an object §Objects are encapsulated which means that there is no way to access an object except through the public interface - a set of operations - specified for it §To emphasize object independence, objects communicate by message passing §A class is a template that special operations (like new) can use to create new objects §Inheritance makes it possible to declare a class as a specialization of another class, thus supporting the management of (hierarchical) relationships among classes as well as the reusability of software §The ability of different objects to respond differently to the same message is known as polymorphism §The concepts of inheritance and polymorphism can best be exploited if the underlying system supports run-time type checking and late binding - operation names are translated into program addresses at run-time O-O Databases: Top-Down & Bottom-Up Approach §Historical roots in –database technology, including semantic data models –abstraction-based programming languages, e.g., Simula-67, Smalltalk