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Chapter 1. Introduction to Software Engineering

Define Software.

The term Software Engineering was first used at a NATO conference in 1968

The term software refers to the set of computer programs, procedures, and associated

documents (flowcharts, manuals, etc.) that describe the programs and how they are to be

used

What are the components of Software?

Software is not just the programs but also all associated documentation and configuration

data which is needed to make these programs operate correctly

A software system usually consists of:

A number of separate programs

Configuration files which are used to set up these programs

System documentation which describes the structure of the system

User documentation which explains how to use the system

For software products, web sites for users to download recent product information

Define Software Engineering.

Software engineering is an engineering discipline which is concerned with all aspects of

software production from the early stages of system specification through to maintaining

the system after it has gone into use (Software Life Cycle)

Define Software Life-Cycle Model.

A software life cycle model depicts the significant phases of a software project fromconception until the product is retired

It addresses the phases of a software project: requirements phase, design phase,

implementation, integration, testing, operation and maintenance phases

Discuss the importance of software.

It is the engine that drives business decision-making

It serves as the basis for modern scientific investigation and engineering problem-solving

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It is embedded in all kinds of systems, such as transportation, medical,

telecommunications, military, industrial processes, entertainment, etc

Software is important as it affects nearly every aspect of our lives and has become

pervasive in our commerce, our culture, and our everyday activities

As software importance grows, the software community continually attempts to developtechnologies that will make it easier, faster, and less expensive to build high-quality

computer programs

What are the types of software?

System Software:

Operating Software Utilities Compilers Debuggers Assemblers.

Application Software:

Word processors Spreadsheets - database management systems.

What are the classes of software?

I. Generic Software

Generic software is designed for a broad customer market whose requirements are very common,

fairly stable, and well-understood by the software engineer

Generic software products are sold in the open market, and there could be several

competitive products on the market

Database products, browsers, and system software are examples of generic software

II. Customized Software

Customized products are those that are developed for a customer where domain,

environment, and requirements are unique to that customer and cannot be satisfied by generic

products

Legacy systems, software written for specific business processes that are typical of thespecific industry, are used when a customized software product is needed

Process-control systems and hospital-management systems require customized software

The developer manages a generic product and the customer manages a customized

product

In other words, requirements and specifications of a generic product are controlled by the

developer, whereas in the case of a customized product, these are controlled by the

customer and influenced by the practices of that industry

Explain the characteristics of software.

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1. Most software is custom-built, rather than assembled from existing components

2. Software is developed or engineered; it is not manufactured in the classical sense

3. Software is flexible

4. Software doesnt wear out

Discuss the software crisis.

Problems:

Schedule and cost estimates are often grossly inaccurate

The productivity of software people hasnt kept pace with the demand for their services

The quality of software is sometimes less than adequate

With no solid indication of productivity, we cant accurately evaluate the efficiency of

new tools, methods, or standards

Communication between the customer and software developer is often poor

Software maintenance tasks devour the majority of all software funds

State some applications of software.

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Chapter 2. Software-Development Life-Cycle Models

What is the software engineering process?

A software process is a set of activities whose goal is the development or evolution of

software

These activities are:

Software specifications - Software development - Software validation - Software

evolution

Explain the reasons for using a software life-cycle model.

Helps to understand the entire process

Enforces a structured approach to development

Enables planning of resources in advance

Enables subsequent controls of them

Aids management to track progress of the system

What is feasibility study?

A feasibility study is a preliminary study which investigates the needs of prospective

users and determines the resource requirements, costs, benefits, and feasibility of a

proposed project

The goal of feasibility studies is to evaluate alternative systems and to propose the most

feasible and desirable systems for development

What are the categories of feasibility study?

Organizational Feasibility:

Organizational feasibility is how well a proposed information system supports the

objectives of the organization

For example, projects that do not directly contribute to meeting an organizations strategic

objectives are typically not funded

Economic Feasibility:

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Economic feasibility is concerned with whether expected cost savings, increased revenue,

reductions in required investments, and other types of benefits will exceed the costs of

developing and operating a proposed system

Technical Feasibility:

Technical feasibility can be demonstrated if reliable hardware and software capable ofmeeting the needs of a proposed system can be acquired or developed by the business in

the required time

Operational Feasibility:

Operational feasibility is the willingness and ability of management, employees,

customers, suppliers, and others to operate, use, and support a proposed system

If the software for a new system is too difficult to use, employees may make too many

errors and avoid using it

What is software maintenance?

Maintenance is an important part of the SDLC

Many times maintenance may consume more time than the time consumed in the

development

The cost of maintenance varies from 50% to 80% of the total development cost

What are the types of software maintenance.

1. Corrective Maintenance:

Corrective maintenance means repairing processing or performance failures or making

changes because of previously uncorrected problems

2. Adaptive Maintenance:

Adaptive maintenance means changing the program function. This is done to adapt to the

external environment change

3. Perfective Maintenance:

Perfective maintenance means enhancing the performance or modifying the programs to

respond to the users additional or changing needs

4. Preventive Maintenance:

Preventive maintenance is the process by which we prevent our system from being

obsolete

It involves the concept of re-engineering and reverse engineering in which an old system

with an old technology is re-engineered using new technology

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State the set of documents produced in a software project.

Requirements document

Project plan

Design documents (architecture, detailed)

Test plan and test reports

Final code

Software manuals (e.g., user, installation, etc.)

Explain the waterfall process model.

Phase 1: Feasibility Study:

Its result is a document that should contain at least the following items:

A definition of the problem

Determination of technical and economic viability

Alternative solutions and their expected benefits

Required resources, costs, and delivery dates in each proposed alternative solution

Phase 2: Requirement Analysis and Specification:

An SRS (Software Requirements Specification) document must contain the following:

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Detailed statement of problem

Possible alternative solution to problem

Functional requirements of the software system

Constraints on the software system

Phase 3: Design and Specification:

Traditional Design Approach:

Architectural design (also called high-level design

Detailed design (also called low-level design)

Object-Oriented Design Approach:

Lower development time and effort

Better maintainability

Phase 4: Coding and Module Testing:

Output of this phase is an implemented and tested collection of modules

Phase 5: Integration and System Testing:

Integration is normally carried out incrementally over a number of steps

The system testing is done in three phases:

Alpha Testing

Beta Testing

Acceptance Testing

Phase 6: Delivery and Maintenance:

The delivery of software is often done in two stages

The cost of maintenance is often more than 60% of the total cost of software

Over 50% of maintenance costs attributed to perfective maintenance

Evolution is probably a better term than maintenance

State the advantages and disadvantages of Waterfall model.

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The main advantage of the waterfall model is its simplicity. It is straightforward and

divides the large task of building a software system into a series of cleanly divided phases,

each phase dealing with a separate logical concern

Waterfall model is also easy to administer in a contractual setup. As each phase is

completed and its work product produced, some amount of money is given by the

customer to the developing organization

The disadvantages of Waterfall Model

It assumes that the requirements of a system can be frozen before the design begins

Freezing the requirements usually requires choosing the hardware

It follows the big bang approach. The entire software is delivered in one shot at the end

It encourages requirements bloating

It is a document-driven process that requires formal documents at the end of each phase

Despite these limitations, the waterfall model has been the most widely used process

model

If the developing organization is quite familiar with the problem domain and the

requirements for the software are quite clear, the waterfall model works well, and may be

the most efficient process

Explain the Time-Boxing process model.

In the time boxing model, the basic unit of development is a time box, which is of fixed

duration

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Since the duration is fixed, a key factor in selecting the requirements to be built in a time

box is what can be fit into the time box

Each time box is divided into a sequence of stages

The model requires that the duration of each stage is approximately the same

Having time-boxed iterations with stages of equal duration and having dedicated teams

renders itself to pipelining of different iterations

To illustrate the use of this model, consider a time box consisting of three stages:

requirement specification, build, and deployment.

The requirement stage is executed by its team of analysts and ends with a prioritized list

of requirements to be built in this iteration along with a high-level design

The build team develops the code for implementing the requirements, and performs the

testing

The tested code is then handed over to the deployment team, which performs

predeployment tests, and then installs the system for use

These three stages can be done in approximately equal time in an iteration

What are the common principles for agile approaches?

Working software is the key measure of progress in a project

For progress in a project, software should be developed and delivered rapidly in smallincrements

Even late changes in the requirements should be entertained

Face-to-face communication is preferred over documentation

Continuous feedback and involvement of customer is necessary for developing good-

quality software

Simple design which evolves and improves with time is a better approach than doing an

elaborate design up front for handling all possible scenarios

The delivery dates are decided by empowered teams of talented individuals

Explain the extreme programming process.

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Many detailed agile methodologies have been proposed, some of which are widely used

now

Extreme programming (XP) is one of the most popular and well-known approaches in the

family of agile methods

XP UNIQUE PRACTICES

The XP approach used in an development iteration has some unique practices:

Development is done by pairs of programmers (called pair programming), instead of

individual programmers

Automated unit tests are written first before the actual code is written, and then the code

should be written to pass the tests (test-driven development)

It suggests that refactoring be done to improve the design. During refactoring, no new

functionality is added, only the design of the existing programs is improved

It encourages frequent integration of different units. Only one pair at a time can release

their changes and integrate into the common code base

Design your own development process for the following software project: The client

is willing to spend some time only three times to help develop the requirements

(divide the requirements phase into three equal parts) - The system is designed to

automate an existing manual system - The client wanted to reduce the delivery time

as much as possible - The developing organization is quite familiar with the problem

domain - The project requires a large number of features.

We divide the project into three subprojects. For each one, we use waterfall model for

requirements phase, and time boxing model for the remaining phases of each subproject.


is willing to spend some time at the start to help develop the requirements - The

client wanted to reduce the delivery time as much as possible - The developing

organization is not familiar with the problem domain - The project requires a large

number of features.

We use prototyping model for requirements phase, and time boxing model for the remaining

phases of each subproject.

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is willing to spend some time at the start to help develop the requirements - The

client wanted to improve cash flow and get benefits as soon as possible - The

developing organization is not familiar with the problem domain.

We use waterfall model for requirements phase, and iterative delivery model for the remaining

phases of each subproject.

Design your own development process for the following software project: The pace

of requirements change is high - The customer is willing to be heavily involved

during the entire development.

We use extreme programming model for this project

Chapter 3. Introduction to Software Requirements Specification

What are the types of requirements?

On the basis of their functionality, the requirements are classified into the following two

types:

Functional requirements: They define factors, such as I/O formats, storage structure,computational capabilities, timing, and synchronization

Non-functional requirements: They define the properties or qualities of a product

including usability, efficiency, performance, reliability, portability, etc

Explain the process of requirements engineering.

.

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State the types of requirements review.

Informal Review

Formal Review

Verifiability

Comprehensibility

Traceability

Adaptability

What are the classes of requirements?

Enduring requirements : These are relatively stable requirements which derive from thecore activity of the organization and which relate directly to the domain of the system

Volatile requirements : These are requirements which are likely to change during the

system development or after the system has been put into operation

Construct a DFD that describes the arithmetic expression (a + b) * (c + a * d). Assume that

the data a, b, c, and d are read from a terminal and the result is printed

Construct a DFD that describes a simplified information system for a public library. The

data and functions shown are not necessarily computer data and computer functions. TheDFD describes physical objects, such as books and shelves, together with data stores that

are likely to be, but are not necessarily, realized as computer files

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Construct a decision table for the following: The Head of the Department (HOD) in a

faculty recommends books to be bought by the Library. If funds are available, then the

books are bought. In case funds dont permit, a textbook is kept waitlisted for purchase

during the next year, whereas the Library returns the requisitions for all other books to the

Head of the Department

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Draw a Basic Use Case Diagram for an ATM System.

Write three textual use-cases for an on-line auction system

On-line auction system is to be built for a university community, called the University

Auction System (UAS), through which different members of the university can sell and

buy goods

We will assume that there is a separate financial subsystem through which the payments

are made and that each buyer and seller has an account in it

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Let us first consider the main use cases of this systemput an item for auction, make

a bid, and complete an auction. These use cases are given below

Textual Use Cases UC1



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Draw a sequence diagram for a restaurant.

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