B.Sc. IT BT8901 (Semester 5, Object Oriented Systems) Assignment

Fall 2013 Assignment

Bachelor of Science in Information Technology (BSc IT) – Semester 5

BT8901 – Object Oriented Systems – 4 Credits

(Book ID: B1185)

Assignment Set (60 Marks)

1.      Write a note on Principles of Object Oriented Systems.

Ans.-   The object model comes with a lot of terminology. A Smalltalk programmer uses methods, a C++ programmer uses virtual member functions, and a CLOS programmer uses generic functions. An Object Pascal programmer talks of a type correct, an Ada programmer calls the same thing a type conversion. To minimize the confusion, let‟s see what object orientation is.

Bhaskar has observed that the phrase object-oriented “has been bandied about with carefree abandon with much the same reverence accorded „motherhood,‟ „apple pie,‟ and „structured programming‟”. We can agree that the concept of an object is central to anything object-oriented. Stefik and Bobrow define objects as “entities that combine the properties of procedures and data since they perform computations and save local state”. Defining objects as entities asks the question somewhat, but the basic concept here is that objects serve to unify the ideas of algorithmic and data abstraction. Jones further clarifies this term by noting that “in the object model, emphasis is placed on crisply characterizing the components of the physical or abstract system to be modeled by a programmer system…. Objects have a certain „integrity‟ which should not – in fact, cannot – be violated. An object can only change state, behave, be manipulated, or stand in relation to other objects in ways appropriate to that object. An object is characterized by its properties and behavior.

Object-Oriented Programming:- Object-oriented programming is a method of implementation in which programs are organized as cooperative collections of objects, each of which represents an instance of some class, and whose classes are all members of a hierarchy of classes united via inheritance relationships.

There are three important parts to this definition: object-oriented programming (1) uses objects, not algorithms, as its fundamental logical building blocks (2) each object is an instance of some class, and (3) classes are related to one another via inheritance relationships.

Object-Oriented Design:- Generally, the design methods emphasize the proper and effective structuring of a complex system. Let‟s see the explanation for object oriented design.

Object-oriented design is a method of design encompassing the process of object-oriented decomposition and a notation for depicting both logical and physical as well as static and dynamic models of the system under design.

There are two important parts to this definition: object-oriented design (1) leads to an object-oriented decomposition and (2) uses different notations to express different models of the logical (class and object structure) and physical (module and process architecture) design of a system, in addition to the static and dynamic aspects of the system.

Object-Oriented Analysis:- Object-oriented analysis (or OOA, as it is sometimes called) emphasizes the building of real-world models, using an object-oriented view of the world. Object-oriented analysis is a method of analysis that examines requirements from the perspective of the classes and objects found in the vocabulary of the problem domain.

2.      What are objects? Explain characteristics of objects.

Ans.-   The term object was first formally utilized in the Simula language. The term object means a combination of data and logic that represents some real world entity.

When developing an object-oriented application, two basic questions always rise:

What objects does the application need?

What functionality should those objects have?

Programming in an object-oriented system consists of adding new kinds of objects to the system and defining how they behave.

The different characteristics of the objects are:

i) Objects are grouped in classes:- A class is a set of objects that share a common structure and a common behavior, a single object is simply an instance of a class. A class is a specification of structure (instance variables), behavior (methods), and inheritance for objects.

Anbu, Bala, Chandru, Deva, and Elango are instances or objects of the class Employee

Attributes: Object state and properties

Properties represent the state of an object. For example, in a car object, the manufacturer could be denoted by a name, a reference to a manufacturer object, or a corporate tax identification number. In general, object’s abstract state can be independent of its physical representation.

The attributes of a car object

ii) Objects have attributes and methods:- A method is a function or procedure that is defined for a class and typically can access the internal state of an object of that class to perform some operation. Behavior denotes the collection of methods that abstractly describes what an object is capable of doing. Each procedure defines and describes a particular behavior of the object. The object, called the receiver, is that on which the method operates. Methods encapsulate the behavior of the object. They provide interfaces to the object, and hide any of the internal structures and states maintained by the object.

iii) Objects respond to messages:- Objects perform operations in response to messages. The message is the instruction and the method is the implementation. An object or an instance of a class understands messages. A message has a name, just like method, such as cost, set cost, cooking time. An object understands a message when it can match the message to a method that has a same name as the message. To match up the message, an object first searches the methods defined by its class. If it is found, that method is called up. If not found, the object searches the superclass of its class. If it is found in a superclass, then that method is called up. Otherwise, it continues the search upward. An error occurs only if none of the superclasses contain the method.

Different objects can respond to the same message in different ways. In this way a message is different from a subroutine call. This is known as polymorphism, and this gives a great deal of flexibility. A message differs from a function in that a function says how to do something and a message says what to do. Example: draw is a message given to different objects.

Objects respond to messages according to methods defined in its class.

3.      What are behavioral things in UML mode? Explain two kinds of behavioral things.

Ans.-   Behavioral things are the dynamic parts of UML models. These are the verbs of a model, representing behavior over time and space. In all, there are two primary kinds of behavioral things.

1. Interaction

2. State Machine

Interaction: An interaction is a behavior that comprises a set of messages exchanged among a set of objects within a particular context to accomplish a specific purpose. The behavior of a society of objects or of an individual operation may be specified with an interaction. An interaction involves a number of other elements, including messages, action sequences (the behavior invoked by a message), and links (the connection between objects). Graphically, an interaction (message) is rendered as a directed line, almost always including the name of its operation, as in below Figure.

Interaction (message)

State Machine: A state machine is a behavior that specifies the sequences of states an object or an interaction that goes through during its lifetime in response to events, together with its responses to those events. The behavior of an individual class or a collaboration of classes may be specified with a state machine. A state machine involves a number of other elements, including states, transitions (the change from one state to another state), events (things that trigger a transition), and activities (the response to a transition). Graphically, a state is rendered as a rounded rectangle, usually including its name and its sub states, if any, as in below Figure.

State

4.      Write a short note on Class-Responsibility-Collaboration (CRC) Cards.

Ans.-   A Class Responsibility Collaborator (CRC) model (Beck & Cunningham 1989; Wilkinson 1995; Ambler 1995) is a collection of standard index cards that have been divided into three sections, as depicted in Figure 1. A class represents a collection of similar objects, a responsibility is something that a class knows or does, and a collaborator is another class that a class interacts with to fulfill its responsibilities.  Figure 2 presents an example of two hand-drawn CRC cards.

Figure 1. CRC Card Layout.

Figure 2. Hand-drawn CRC Cards.

Although CRC cards were originally introduced as a technique for teaching object-oriented concepts, they have also been successfully used as a full-fledged modeling technique. My experience is that CRC models are an incredibly effective tool for conceptual modeling as well as for detailed design.  CRC cards feature prominently in eXtreme Programming (XP) (Beck 2000) as a design technique.  My focus here is on applying CRC cards for conceptual modeling with your stakeholders.

A class represents a collection of similar objects. An object is a person, place, thing, event, or concept that is relevant to the system at hand. For example, in a university system, classes would represent students, tenured professors, and seminars. The name of the class appears across the top of a CRC card and is typically a singular noun or singular noun phrase, such as Student, Professor, and Seminar. You use singular names because each class represents a generalized version of a singular object. Although there may be the student John O’Brien, you would model the class Student. The information about a student describes a single person, not a group of people. Therefore, it makes sense to use the name Student and not Students. Class names should also be simple. For example, which name is better: Student or Person who takes seminars?

A responsibility is anything that a class knows or does. For example, students have names, addresses, and phone numbers. These are the things a student knows. Students also enroll in seminars, drop seminars, and request transcripts. These are the things a student does. The things a class knows and does constitute its responsibilities. Important: A class is able to change the values of the things it knows, but it is unable to change the values of what other classes know.

Sometimes a class has a responsibility to fulfill, but not have enough information to do it. For example, as you see in Figure 3 students enroll in seminars. To do this, a student needs to know if a spot is available in the seminar and, if so, he then needs to be added to the seminar. However, students only have information about themselves (their names and so forth), and not about seminars. What the student needs to do is collaborate/interact with the card labeled Seminar to sign up for a seminar. Therefore, Seminar is included in the list of collaborators of Student.

Figure 3. Student CRC card.

Collaboration takes one of two forms: A request for information or a request to do something. For example, the card Student requests an indication from the card Seminar whether a space is available, a request for information.Student then requests to be added to the Seminar, a request to do something. Another way to perform this logic, however, would have been to have Student simply request Seminar to enroll himself into itself. Then have Seminardo the work of determining if a seat is available and, if so, then enrolling the student and, if not, then informing the student that he was not enrolled.

5.      Explain Modern Hierarchical Teams. Also draw its structure.

Ans.-   As just mentioned, the problem with traditional programmer teams is that it is all but impossible to find one individual who is both a highly skilled programmer and a successful manager. The solution is to use a matrix organizational structure and to replace the chief programmer by two individuals: a team leader, who is in charge of the technical aspects of the team‟s activities, and a team manager, who is responsible for all non-technical managerial decisions. The structure of the resulting team is shown in below figure.

Figure:-The Structure of a Modern Hierarchical Programming Team

It is important to realize that this organizational structure does not violate the fundamental managerial principle that no employee should report to more than one manager. The areas of responsibility are clearly delineated. The team leader is responsible for only technical management. Thus, budgetary and legal issues are not handled by the team leader, nor are performance appraisals. On the other hand, the team leader has sole responsibility on technical issues. The team manager, therefore, has no right to promise, say, that the information system will be delivered within four weeks; promises of that sort have to be made by the team leader.

Before implementation begins, it is important to demarcate clearly those areas that appear to be the responsibility of both the team manager and the team leader. For example, consider the issue of annual leave. The situation can arise that the team manager approves a leave application because leave is a non-technical issue, only to find the application vetoed by the team leader because a deadline is approaching. The solution to this and related issues is for higher management to draw up a policy regarding those areas that both the team manager and the team leader consider to be their responsibility.

6.      Explain in brief the five levels of CMM.

Ans.-   A maturity level is a well-defined evolutionary plateau toward achieving a mature software process. Each maturity level provides a layer in the foundation for continuous process improvement.

In CMMI models with a staged representation, there are five maturity levels designated by the numbers 1 through 5

1.      Initial

2.      Managed

3.      Defined

4.      Quantitatively Managed

5.      Optimizing

CMMI Staged Represenation- Maturity Levels

Maturity Level 1 - Initial

At maturity level 1, processes are usually ad hoc and chaotic. The organization usually does not provide a stable environment. Success in these organizations depends on the competence and heroics of the people in the organization and not on the use of proven processes.

Maturity level 1 organizations often produce products and services that work; however, they frequently exceed the budget and schedule of their projects.

Maturity level 1 organizations are characterized by a tendency to over commit, abandon processes in the time of crisis, and not be able to repeat their past successes.

Maturity Level 2 - Managed

At maturity level 2, an organization has achieved all the specific and generic goals of the maturity level 2 process areas. In other words, the projects of the organization have ensured that requirements are managed and that processes are planned, performed, measured, and controlled.

The process discipline reflected by maturity level 2 helps to ensure that existing practices are retained during times of stress. When these practices are in place, projects are performed and managed according to their documented plans.

At maturity level 2, requirements, processes, work products, and services are managed. The status of the work products and the delivery of services are visible to management at defined points.

Maturity Level 3 - Defined

At maturity level 3, an organization has achieved all the specific and generic goals of the process areas assigned to maturity levels 2 and 3.

At maturity level 3, processes are well characterized and understood, and are described in standards, procedures, tools, and methods.

A critical distinction between maturity level 2 and maturity level 3 is the scope of standards, process descriptions, and procedures. At maturity level 2, the standards, process descriptions, and procedures may be quite different in each specific instance of the process (for example, on a particular project). At maturity level 3, the standards, process descriptions, and procedures for a project are tailored from the organization's set of standard processes to suit a particular project or organizational unit. The organization's set of standard processes includes the processes addressed at maturity level 2 and maturity level 3. As a result, the processes that are performed across the organization are consistent except for the differences allowed by the tailoring guidelines.

Maturity Level 4 - Quantitatively Managed

At maturity level 4, an organization has achieved all the specific goals of the process areas assigned to maturity levels 2, 3, and 4 and the generic goals assigned to maturity levels 2 and 3.

At maturity level 4 Subprocesses are selected that significantly contribute to overall process performance. These selected subprocesses are controlled using statistical and other quantitative techniques.

Quantitative objectives for quality and process performance are established and used as criteria in managing processes. Quantitative objectives are based on the needs of the customer, end users, organization, and process implementers. Quality and process performance are understood in statistical terms and are managed throughout the life of the processes.

For these processes, detailed measures of process performance are collected and statistically analyzed. Special causes of process variation are identified and, where appropriate, the sources of special causes are corrected to prevent future occurrences.

Maturity Level 5 - Optimizing

At maturity level 5, an organization has achieved all the specific goals of the process areas assigned to maturity levels 2, 3, 4, and 5 and the generic goals assigned to maturity levels 2 and 3.

Processes are continually improved based on a quantitative understanding of the common causes of variation inherent in processes.

Maturity level 5 focuses on continually improving process performance through both incremental and innovative technological improvements.

Quantitative process-improvement objectives for the organization are established, continually revised to reflect changing business objectives, and used as criteria in managing process improvement.

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