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Chapter 1: Concepts for Object-Oriented Databases
The following object-oriented concepts are typically associated with an
(Object Database)ODB:
1.1. Overview of Object-Oriented Concepts
1.2. Object Identity, Object Structure, and Type Constructors
1.3. Encapsulation of Operations, Methods, and Persistence
1.4. Type Hierarchies and Inheritance
What is object?
Object consists of entity and attributes which can describe the state of realworld object and action associated with the object.eg car,boat
 class
 method and persistence
 encapsulation
 encapsulation
 complex objects
 extensibility
 object identity
 polymorphism
 object structure
 class hierarchies and inheritance
 object constructor
 overriding, overloading
Cont….

Through object-based database system we are really incorporating the features
of object-oriented programming like objects, class, and inheritance.
Object-based database system
Simply object-oriented database system should satisfy two criteria:
 In object-oriented database, information is represented (that is stored and
a. It should be DBMS
manipulated) is all in the form of object.
 Object oriented database are the same as object-oriented programming
languages.
b. It should be object-oriented system
Note OODB implements OO concepts such as object identity, polymorphism,
encapsulation, and inheritance to provides access to persistent objects using any
object-oriented programming languages.
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Some important characteristics of an object are:
1. Object name: -the name is used to refer different object in the program
2. Object identifier: - this the system generated identifier which is assigned,
RDBMS and OODBMS are database management systems. RDBMS uses tables to
represent data and their relationships whereas OODBMS represents data in form of objects
similar to Object Oriented Programming.
Following are the important differences between RDBMS and OODBMS.
Sr.
when a new object is created.
4. Transient object: - in OOPL, object which are present only at the time of
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execution are called transient object.
5. Persistent object: - an object which exists even after the program is
completely executed or terminated, is called persistent object. Object database
Data
An entity refers to collection of similar
An class refers to group of objects having
items having same definition.
common relationships, behaviors and
RDBMS handles only data.
Handling
Definition
RDBMS stands for Relational DataBase
OODBMS stands for Object Oriented
Management System.
DataBase Management System.
Data is stored as entities defined in tabular
Data is stored as objects.
Managemen format.
Data
properties.
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OODBMS
t
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Term
RDBMS
Data
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can store objects in secondary memory.
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Key
No.
OODBMS handles both data and functions
operating on that data.
RDBMS handles simple data.
OODBMS handles large and complex data.
Complexity
Features of OODBMS
In OODBMS, every entity is considered as object and represented in a table. Similar object classified to classes
and subclasses and relationship between two object is maintained using concept of inverse references.
1. Complexity: - OODBMS has the ability to represent the complex internal structure (of object) with
multilevel complexity.
2. Inheritance: - creating new object from existing objects in such a way that new object inherits all
characteristic of an existing objects.
Objective
To keep data independent from application To implement data encapsulation.
program.
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3. Encapsulation: - it is a data hiding concepts in OOPL which binds the data and function togethers which can
manipulate data and not visible to the outside world.
4. User define abstract data types (ADT): - ADT allow new data types with structure suited to particular
Key
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A primary key identifies in object in a table Object Id, OID represents an object
uniquely.
uniquely in group of objects.
application to be defined.
5. Persistency: - OODBMS allow to create persistent object (object remain in memory even after execution).
This feature can solve the problem of recovery and concurrency.
6. Object Identity: - OID(Object identify digitally) are used to identify objects.
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Properties of OID
Object Identity
 An object identity is an internal identifier of object that could not be
changed. An object identity (iod) remains constant during object
1. Uniqueness: OID cannot be the same to every object in the system and its
generated automatically by the system.
lifetime. Every object has unique identity. In object-oriented system,
2. Invariant: OID cannot be changed throughout its entire lifetime.
when object is created IOD is assigned to it.
3. Invisible: OID is not visible to user.
 In RDBMS OID is value based and primary key is used to provide
Object Structure
uniqueness of each table in relation. Primary key is chosen from the
 A class object contains information about the state described by attributes
attributes of the relation which makes object independent on the object
and the behavior allowed by methods. An attribute and a method that are for
states.
the instances of the class are called instance attribute and an instance method.
For Example
Student
Instance
Attribute
Stid
Fname
LName
Type Constructors
Object Instance
001
Bekel
Ayele
 Type Constructors Also called type generator, a type constructor is particular
kind of method in a class. It is called to create an object of this class and initialize
its attributes. The constructor has the same name as the class. Unlike to ordinary
methods, the constructor has not explicit return type.
 The three most basic constructors are atom, tuple, and set.
 The atom constructor is used to represent all basic atomic values, such as
integers, real numbers, character strings, Booleans, and any other basic data types
that the system supports directly.
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Type constructor
Used
Atom
the basic built-in data types of the object model Like
integers, strings, floating point numbers, enumerated types,
Booleans, and so on
Struct (tuple)
create standard structured types, such as the tuples (record
types)
in the basic relational model.
Set(T)
Create objects or literals that are a set of distinct elements all
of the same type.
Class
A class essentially defines the type of the object where each object is viewed as an
instance of the class. For example, Person is a class and Kebede is an instance or an object
of this class.
Eg: Class Definition : defining the class BRANCH
BRANCH
Attributes
brabchNo
street
city
postcode
Methods
Print()
getPostCode()
numberofStaff()
Complex Objects
 Complex objects or nested relations are objects which are designed by
combining simple objects. These objects used to be created by constructors.
Encapsulation
Encapsulation is the ability to group data and mechanisms into a single object to provide access protection.
Through this process, pieces of information and details of how an object works are hidden, resulting in data and
function security. Classes interact with each other through methods without the need to know how particular
methods work.
 An airplane and a car are examples of complex objects because they can be
viewed as a higher-level object that is constructed from lower-level objects, such
as engine and body (for both), the airplane wings and tail.
 Each of these objects can be complex objects that are constructed from other
simple or complex objects.
As an example, a car has descriptive characteristics and actions. You
can change the color of a car, yet the model or make are examples of
properties that cannot change. A class encapsulates all the car
information into one entity, where some elements are modifiable while
some are not.
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Methods
Persistence
 Storing permanently the values of properties of an object is called
 In object-oriented approach, the behavior of an object is described by a set of
object persistence. In other words, persistence refers to the ability for
operations that are called methods. A method has a signature that describes the name of
objects to remain after stopping the process that created them.
 The properties of persistent object are created and stored in main
memory. Object-oriented database systems are based on the concept of
persistent objects.
the method and the names and types of the method parameters.
 A method is a particular implementation of a method signature. They are defined in
object class and allow to relate different others objects and manipulating them.
Example: When an employee is fired, we need to delete the employee information from
the employee file, delete the employee from the employee-project file, and insert the
employee information into a history file, etc.
One method called “Fire-employee” can be defined that incorporates this sequence of
Class Hierarchy
Type Hierarchies & Inheritance
 In object-oriented approach, there is the possible to define class
hierarchies and to express the inheritance of state and behavior.
Example:-Manger is a Employee
 A class hierarchy provides an inheritance mechanism which allows a class to
inherit properties (attributes and methods) from its super classes.
Example
Person
 In single inheritance systems, a class can have at most one direct superclass and
therefore can only inherit from that superclass. The class hierarchy forms a tree.
Employee
Student
Teacher
The ODB have advantages to completely support class hierarchies and
inheritance.
 In multiple inheritance systems, a class can have more than one direct superclass.
The Multiple class hierarchy is a lattice.
Note: In multiple inheritance systems, a class may inherit properties and methods
from different super classes and therefore may have inheritance conflicts.
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Reading Assignment:
Some problems and proposed solutions in Object-Oriented Data Models.
 General disagreement on OO concepts
 Issues in Use of Methods
 Standard Declarative Query Language
 Access Methods and Data Type Extensibility
 Support for complex objects
 Object Identity
 Should attributes be directly accessible?
 Every thing as Objects?
 Formal Foundation for OO paradigm
 Conflicts in Class Hierarchy and Multiple Inheritance and etc.
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