1. Object Oriented Databases - Overview
ADVANCED DATABASES
Object Oriented Databases - Overview
Khawaja Mohiuddin
Assistant Professor
Department of Computer Sciences
Bahria University (Karachi Campus)
Contents for this lecture are taken from:
Chapter 10 of “Database Systems: Models, Languages …”, 6th Ed.” by Elmasri and Navathe
(Chapter 11 of “Fundamentals of Database Systems” 6th Ed. by Elmasri and Navathe)

2. Objectives To cover an overview of following concepts Object identity
Type constructor
Encapsulation of operations
Programming language compatibility
Type hierarchies and inheritance
Extents
Polymorphism and operator overloading

3. Object and Object-Relational Databases
Object databases (ODB, previously called OODB)
Object Data Management Systems (ODMS, previously called ODBMS or OODBMS
Why:
To cater the need for new data types for complex structures, for storing images, videos, or large textual items; longer-duration transactions, etc.
To directly or seamlessly integrate with software that is developed using object-oriented programming languages.
Specify:
Structure of complex objects
Operations that can be applied to these objects

4. Overview of Object Database Concepts
Introduction to object-oriented concepts and features
Origins in OO programming languages
Object has two components:
State (value) and behavior (operations)
Instance variables
Hold values that define internal state of object
Operation is defined in two parts:
Signature or interface and implementation

5. Overview of Object Database Concepts (cont’d.)
Inheritance
Permits specification of new types or classes that inherit much of their structure and/or operations from previously defined types or classes
Operator overloading
Operation’s ability to be applied to different types of objects
Operation name may refer to several distinct implementations

6. Object Identity, and Objects versus Literals
Unique identity
Implemented via a unique, system-generated object identifier (OID)
Immutable (can not be changed)
Most OO database systems allow for the representation of both objects and literals (or values)

7. Complex Type Structures for Objects and Literals
Structure of arbitrary complexity
Contain all necessary information that describes object or literal
Nesting type constructors
Construct complex type from other types
Most basic constructors:
Atom: Includes basic built-in data types, such as integers, strings, floating point numbers, enumerated types, Booleans, and so on. Each value of the type is considered an atomic (indivisible) single value

8. Complex Type Structures for Objects and Literals (cont’d.)
Struct (or tuple): Made up of several components, and is also sometimes referred to as a compound or composite type.
Collection Allow part of an object or literal value to include a collection of other objects or values when needed.

9. Complex Type Structures for Objects and Literals (cont’d.)
Collection types:
Set - objects or literals that are a set of distinct elements {i1, i2, ..., in}, all of the same type
Bag - similar to a set except that the elements in a bag need not be distinct
List - an ordered list [i1, i2, ..., in] of OIDs or values of the same type
Array - a fixed size, single-dimensional array of elements of the same type

10. Complex Type Structures for Objects and Literals (cont’d.)
Collection types (cont’d):
Dictionary - a collection of two tuples (K, V), where the value of a key K can be used to retrieve the corresponding value V
Object definition language (ODL)
Used to define object types for a particular database application

12. Encapsulation of Operations and Persistence of Objects
Related to abstract data types and information hiding in programming languages
Define behavior of a type of object based on operations that can be externally applied
External users only aware of interface of the operations
Divide structure of object into visible and hidden attributes

13. Encapsulation of Operations
Object constructor
Used to create a new object
Destructor operation
Used to destroy (delete) an object
Modifier operations
Modify the states (values) of various attributes of an object
Retrieve information about the object
Dot notation used to apply operations to object

14. Persistence of Objects
Transient objects
Exist in executing program
Disappear once program terminates
Persistent objects
Stored in database and persist after program termination
Naming mechanism (Involves giving an object a unique persistent name within a particular database)
Reachability (by making the object reachable from some other persistent object. An object B is said to be reachable from an object A if a sequence of references in the database lead from object A to object B)

15. Persistence of Objects (cont’d.)

16. Type Hierarchies and Inheritance
Definition of new types based on other predefined types
Leads to type (or class) hierarchy
Type: type name and list of visible (public) functions
Format:
TYPE_NAME: function, function, ..., function

17. Type Hierarchies and Inheritance (cont’d.)
Subtype
Useful when creating a new type that is similar but not identical to an already defined type
Example:
EMPLOYEE subtype-of PERSON: Salary, Hire_date, Seniority
STUDENT subtype-of PERSON: Major, Gpa

18. Type Hierarchies and Inheritance (cont’d.)
Extent
Store collection of persistent objects for each type or subtype
Extents are subsets of the extent of class OBJECT
Persistent collection
Stored permanently in the database
Transient collection
Exists temporarily during the execution of a program

19. Other Object-Oriented Concepts
Polymorphism of operations
Also known as operator overloading
Allows same operator name or symbol to be bound to two or more different implementations
Depending on type of objects to which operator is applied
Can be compile time (static binding) or run time (dynamic binding)
Multiple inheritance
Subtype inherits functions (attributes and methods) of more than one supertype

20. Other Object-Oriented Concepts (cont’d.)
Selective inheritance
Subtype inherits only some of the functions of a supertype

21. Conclusion In this Lecture, we covered following topics
Object identity
Type constructor
Encapsulation of operations
Programming language compatibility
Type hierarchies and inheritance
Extents
Polymorphism and operator overloading