DBMS

1. What is meant by object-oriented data model? 

The object-oriented paradigm is based on encapsulation of data and code related  to an object in to a single unit, whose contents are not visible to the outside world. 

2. What is the major advantage of object-oriented programming paradigm? 

The ability to modify the definition of an object without affecting the rest of the system is the major advantage of object-oriented programming paradigm. 

3. What are the methods used in object-oriented programming paradigm? 

*read-only 

*update 

4. What is the main difference between read-only and update methods? 

A read-only method does not affect the values of a variable in an object, whereas an update method may change the values of the variables. 

5. What is the use of keyword ISA? 

The use of keyword ISA is to indicate that a class is a specialization of another class. 

6. Differentiate sub-class and super-class? 

The specialization of a class is called subclasses.eg: employee is a subclass of  person and teller is a subclass of employee.Conversely, employee is a super class of teller, and person is a super class of employee. 

7. What is substitutability? 

Any method of a class-say A can equally well be invoked with any object belonging to any subclasses B of A. This characteristic leads to code reuse, since the messages, methods, and functions do not have to be written again for objects of class B. 

8. What is multiple inheritance? 

Multiple inheritance permits a class to inherit variables and methods from multiple super classes. 

9. What is DAG? 

The class-subclass relationship is represented by a directed acyclic graph.eg: employees can be temporary or permanenet.we may create subclasses temporary and permanenet, of the class employee. 

10. What is disadvantage of multiple inheritance? 

There is potential ambiguity if the same variable or method can be inherited from more than one uperclass.eg: student class may have a variable dept identifying a student's department, and the teacher class may correspondingly have a variable dept identifying a teacher's department. 

11. What is object identity? 

An object retains its identity even if some or all the values of variables or 

definitions of methods change overtime. 

12. What are the several forms of identity? 

*Value 

*Name 

*Built-in 

13. What is a value? 

A data value is used for identity. This form of identity is used in relational  systems.eg: The primary key value of a tuple identifies the tuple. 

14. What is a Name? 

A user-supplied name is used for identity. This form of identity is used for files in file systems. The user gives each file a name that uniquely identifies it, regardless of its contents. 

15.What is a Built-in 

A notation of identity is built-into the data model or programming language and no user-supplied identifier is required. This form of identity is used in object-oriented systems. 

16 What is meant by object identifiers? 

Object-oriented systems use an object identifier to identify objects. Object identifiers are unique: that is each object has a single identifier, and no two objects have the same identifier. 

17. What are composite objects? 

Objects that contain other objects are called complex objects or composite objects. 

18. What is object containment? 

References between objects can be used to model different real-world concepts. 

19. Why containment is important in oosystems? 

Containment is an important concept in oo systems because it allows different users to view data at different granularities. 

20. Define object-relational systems? 

Systems that provide object-oriented extensions to relational systems are called object-relational systems.