8.
Discuss the main problems of distributed databases.
9.
List and explain any
five
advantages of a distributed database management system.
10.
With help of illustrative diagram, main discuss three architectures of parallel DBMS
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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: Features
i.
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
