OOAD Concepts


Important questions in OOAD Concepts

1. What do you mean by analysis and design?

Analysis: Basically, it is the process of determining what needs to be done before how it should be done. In order to accomplish this, the developer refers the existing systems and documents. So, simply it is an art of discovery.
Design: It is the process of adopting/choosing one among many, which best accomplishes the users needs. So, simply, it is a compromising mechanism.

2. What are the steps involved in designing?

Before getting into the design the designer should go through the SRS prepared by the System Analyst.
The main tasks of design are Architectural Design and Detailed Design.
In Architectural Design we find what are the main modules in the problem domain.
In Detailed Design we find what should be done within each module.

3. What are the main underlying concepts of object orientation?

Objects, messages, class, inheritance and polymorphism are the main concepts of object orientation.

4. What do u meant by “SBI” of an object?

SBI stands for State, Behavior and Identity. Since every object has the above three.
i. State: It is just a value to the attribute of an object at a particular time.
ii. Behaviour: It describes the actions and their reactions of that object.
iii. Identity: An object has an identity that characterizes its own existence. The identity makes it possible to distinguish any object in an unambiguous way, and independently from its state.

5. Differentiate persistent & non-persistent objects?

Persistent refers to an object’s ability to transcend time or space. A persistent object stores/saves its state in a permanent storage system with out losing the information represented by the object.
A non-persistent object is said to be transient or ephemeral. By default objects are considered as non-persistent.

6. What do you meant by active and passive objects?

Active objects are one which instigate an interaction which owns a thread and they are responsible for handling control to other objects. In simple words it can be referred as client.
Passive objects are one, which passively waits for the message to be processed. It waits for another object that requires its services. In simple words it can be referred as server.

7. What is meant by software development method?

Software development method describes how to model and build software systems in a reliable and reproducible way. To put it simple, methods that are used to represent ones’ thinking using graphical notations.

8. What are models and meta models?

Model: It is a complete description of something (i.e. system).
Meta model: It describes the model elements, syntax and semantics of the notation that allows their manipulation.

9. What do you meant by static and dynamic modeling?

Static modeling is used to specify structure of the objects that exist in the problem domain. These are expressed using class, object and USECASE diagrams. But Dynamic modeling refers representing the object interactions during runtime. It is represented by sequence, activity, collaboration and statechart diagrams.

10. How to represent the interaction between the modeling elements?

Model element is just a notation to represent (Graphically) the entities that exist in the problem domain. e.g. for modeling element is class notation, object notation etc.
Relationships are used to represent the interaction between the modeling elements.
The following are the Relationships.

i. Association: It is just a semantic connection between two classes.
ex: class A uses class B

ii. Aggregation: Its’ the relationship between two classes which are related in the fashion that master and slave. The master takes full rights than the slave. Since the slave works under the master. It is represented as line with diamond in the master area.
ex: car contains wheels, etc.

iii. Containment: This relationship is applied when the part contained with in the whole part, dies when the whole part dies. It is represented as darked diamond at the whole part.
class A{
//some code

class B
A aa; // an object of class A;
// some code for class B;

In the above example we see that an object of class A is instantiated with in the class B, so the object of class A dies when the object of class B dies.

iv. Generalization: This relationship used when we want represents a class, which captures the common states of objects of different classes. It is represented as arrow line pointed at the class, which has captured the common states.

v. Dependency: It is the relationship between dependent and independent classes. Any change in the independent class will affect the states of the dependent class.

11. Why is generalization very strong?

Even though Generalization satisfies Structural, Interface, Behaviour properties. It is mathematically very strong, as it is Antisymmetric and Transitive.
Antisymmetric: employee is a person, but not all persons are employees. Mathematically all As’ are B, but all Bs’ not A.
Transitive: A=>B, B=>C then A=>C.
–>A. Salesman.
–>B. Employee.
–>C. Person.

Note: All the other relationships satisfy all the properties like Structural properties, Interface properties, Behaviour properties.

12. Differentiate Aggregation and Containment?

Aggregation is the relationship between the whole and a part. We can add/subtract some properties in the part (slave) side. It won’t affect the whole part. Best example is Car, which contains the wheels and some extra parts. Even though the parts are not there we can call it as car.
But, in the case of containment the whole part is affected when the part within that got affected. The human body is an apt example for this relationship. When the whole body dies the parts (heart etc) are died.

13. Can Link and Association be applied interchangeably?

No, you cannot apply Link and Association interchangeably since Link is used to represent the relationship between the two objects whereas Association is used to represent the relationship between the two classes.
Link :: student:Robert course:CSE
Association:: student course

14. What is meant by “method-wars”?

Before 1994 there were different methodologies like Rumbaugh, Booch, Jacobson, Meyer etc who followed their own notations to model the systems. The developers were in a dilemma to choose the method which best accomplishes their needs. This particular span was called as “method-wars”.

15. Whether unified method and unified modeling language are same or different?

Unified method is convergence of the Rumbaugh and Booch.
Unified modeling language is the fusion of Rumbaugh, Booch and Jacobson as well as Betrand Meyer (whose contribution is “sequence diagram”). It is the superset of all the methodologies.

16. Who were the three famous amigos and what was their contribution to the object community?

The Three amigos namely were:
i. James Rumbaugh (OMT): A veteran in analysis who came up with an idea about the objects and their Relationships (in particular Associations).
ii. Grady Booch: A veteran in design who came up with an idea about partitioning of systems into subsystems.
iii. Ivar Jacobson (Objectory): The father of USECASES, who described about the user and system interaction.

17. What is an USECASE? Why it is needed?

A Use Case is a description of a set of sequence of actions that a system performs that yields an observable result of value to a particular action.
In SSAD process <=> In OOAD USECASE. It is represented elliptically.

18. Who is an Actor?

An Actor is someone or something that must interact with the system.In addition to that an Actor initiates the process (that is USECASE). It is represented as a stickman.

19. What is guard condition?

Guard condition is one, which acts as a firewall. The access from a particular object can be made only when the particular condition is met.
For Example,
customer check customer number ATM.

Here the object on the customer accesses the ATM facility only when the guard condition is met.

20. USECASE is an implementation independent notation. How will the designer give the implementation details of a particular USECASE to the programmer?

This can be accomplished by specifying the relationship called “refinement” which talks about the two different abstraction of the same thing.

21. Suppose a class acts an Actor in the problem domain, how to represent it in the static model?

In this scenario you can use “stereotype”. Since stereotype is just a string that gives extra semantic to the particular entity/model element. It is given with in the << >>.

class A
<< Actor>>

22. Why does the function arguments are called as “signatures”?

The arguments distinguish functions with the same name (functional polymorphism). The name alone does not necessarily identify a unique function. However, the name and its arguments (signatures) will uniquely identify a function.
In real life we see suppose, in class there are two guys with same name, but they can be easily identified by their signatures. The same concept is applied here.
class person
char getsex();
void setsex(char);
void setsex(int);

In the above example we see that there is a function setsex() with same name but with different signature.