Purdue CS307 Software Engineering

8/11/2019 Purdue CS307 Software Engineering

1/30

Object-Oriented Software EngineeringPractical Software Development using UML and Java

Chapter 1:

Software and Software Engineering

1


2/30

2

Prologue

"By the year 2000 all software will contain allfunctions imaginable and will be delivered bug-

free", unknown Software Engineering manager

approximately 1990

By now we expected that software development

would be flawless and that software testing would

be unnecessary


3/30

3

Prologue

Reality -- Software is frequently missing necessaryfunctionality and errors are a more serious problem

today than ever before!

The more computers have to do, the more complex

their software has to be, and therefore the more

difficult it is for software engineers to create high

quality software


4/30

4

1.1 The Nature of Software...

Software is intangible Hard to understand (or even explain) the development

effort required

Software is easy to reproduce

Cost is in its development

in some other engineering products manufacturing

is the costly stage

Software industry is labor-intensive

Hard to automate


5/30

5

The Nature of Software ...

Untrained people can hack something together Quality problems are hard to determine

Software is easy to modify

People make changes without fully understanding their

effects

Software does not wear out

It deterioratesby having its design changed:

erroneously, or

in ways that were not anticipated


6/30

The Nature of Software

Conclusions Much software has poor design

Demand for software is high and rising

We are in a perpetual software crisis

We have to learn to engineer software

6


7/30

7

Types of Software...

Custom For a specific customer

Generic

Sold on open market

Often called

COTS (Commercial Off The Shelf)

Shrink-wrapped

Embedded Built into hardware

Harder to modify


8/30

9

Types of Software

Real time software Control and monitoring systems

Must react immediately

Performance and Safety are major concerns

Data processing software

Used to run businesses

Correctness and Security of data are major concerns

Some software has both aspects


9/30

10

1.2 What is Software Engineering?...

The process of solving customers problems by thesystematic development and evolution of large, high-

quality software systems within cost, time, and other

constraints

Other definitions:

IEEE: (1) the application of a systematic, disciplined, quantifiable approach

to the development, operation, maintenance of software; that is, the

application of engineering to software. (2) The study of approaches as in (1).

The Canadian Standards Association: The systematic activities involved inthe design, implementation and testing of software to optimize its production

and support.


10/30

11

What is Software Engineering?

Solving customers problems This is thegoalof software engineering

Sometimes the solution is to assemble from existing

components, not build from scratch

Sometimes the solution is to buy, not assemble or build

Adding unnecessary features does not help solve

problems

Software engineers must communicate effectivelyto

identify and understand problems


11/30

12


Systematic development and evolution An engineering process involves applying well-

understood techniquesin an organized and disciplined

way

Many well-accepted practices have been formallystandardized

Most development work is evolutionary


12/30

13


Large, high-quality software systems Software engineering techniques are needed because large

systems cannot be completely understoodand developed

by one person (within time constraints)

Teamwork and coordination are required Key challenge: Dividing up the work and ensuring that the

parts of the system will work properly together

The end-product must be of high quality


13/30

14


Cost, time, and other constraints Finite resources

Usually a deadline

The benefits must outweigh the cost

Inaccurate estimates of cost and time have caused many

project failures


14/30

15

1.3 Software Engineering and the

Engineering Profession

The term Software Engineering was coined in 1968 People began to suggest that the principles of

engineering should be applied to software development

Engineering is a licensed profession

In order to protect the public

Engineers design artifacts following well-acceptedpractices which involve the application of science,mathematics, economics, .

Ethical practice is also a key tenet of the profession

In most countries, software engineering does not (yet)require an engineering exam or license


15/30

16

Software Engineering and the Engineering

Profession

Ethics in Software Engineering:

Ethics refers to the concern that humans have for figuring out

how best to live

Like medical, legal and business ethics, engineering ethics is

a well-developed area of professional ethics

Professional engineers today are expected to both learn aboutand live up to ethical standards as a condition of their

membership in the profession


16/30

17


Profession


Software engineering is a relatively young practice and,

compared with other engineering disciplines, its culture of

professionalism is still developing

Software Engineering Code of Ethics and Professional

Practice (Version 5.2) as recommended by the ACM/IEEE-

CS Joint Task Force is the standard for teaching and

practicing software engineering

Software engineers shall adhere to these eightprinciples


17/30

18


Profession


Software engineers shall

1. Act consistently with public interest

2. Act in the best interests of their clients3. Develop and maintain systems using the highest

standards possible

4. Maintain integrity and independence

5. Promote an ethical approach in management

6. Advance the integrity and reputation of the profession

7. Be fair and supportive to colleagues

8. Participate in lifelong learning


18/30

19

1.4 Stakeholders in Software Engineering

1. Users Those who use the software

2. Customers (Project Owners)

Those who pay for the software

3. Software Developers (Software Engineers)

Those who create and maintain the software

4. Development Managers (Project Coordinators)

Those who supervise the software development process


19/30

20

1.5 Software Quality...

Availability Concerned with system failure and its associated

consequences

Modifiability

The cost of change

Performance

How long it takes the system to respond when

an event occurs

Scalability

Can the software handle larger volumes of data?


20/30


21/30


22/30

23

Software Quality and the Stakeholders

QUALITY

SOFTWARE

Developer:

easy to design;

easy to maintain;

easy to reuse its parts

User:

easy to learn;

efficient to use;

helps get work done

Customer:

solves problems atan acceptable cost in

terms of money paid and

resources used

Development manager:

sells more and

pleases customerswhile costing less

to develop and maintain


23/30

24

Software Quality: Conflicts and Objectives

Some software qualities can conflict Increasing efficiency can affect maintainability and/or

reusability

Increasing usability can affect efficiency

Increasing security can affect performanceSetting objectives for quality is a key engineeringactivity

You then design to meet the objectives

Optimizing is always necessary

for example, obtain the highest possible reliability usinga fixed budget


24/30

25

Internal Quality Criteria

Characterize aspects of the designof thesoftware

Have an effect on the external quality attributes

e.g.The amount of commenting of the code

The complexity of the code

The use of well-understood software patterns


25/30

26

Short Term Vs. Long Term Quality

Short term: Does the software meet the customers immediate needs?

Is it sufficiently efficient for the volume of data we have

today?

Long term:

Maintainability

Customers future needs

Scalability


26/30

27

1.6 Software Engineering Projects

Most projects are evolutionaryor maintenanceprojects,involving work on legacysystems

Corrective projects: fixing defects

Adaptive projects: changing the system in response to

changes inOperating system

Database

Organizational operations

Enhancement projects: adding new features for users

Reengineering or perfective projects: changing the

system internally so that it is more maintainable


27/30

28

Software Engineering Projects

Greenfield ProjectFrom scratch project, new development

Lacks any constraints imposed by prior work

Analogy is to construction on greenfield land where there

is no need to remodel or demolish an existing structureMinority of projects

Brownfield Project

Development and deployment of a software system thatmust work with existing software systems

New system must take into account and coexist withalready-existing software


28/30

30

1.7 Activities Common to Software

Projects...

Requirements Includes

Domain analysis

Defining the problem

Requirements gathering

- Obtaining input from as many sources as possible

Requirements analysis

- Organizing the information

Requirements specification

- Writing detailed instructions about how the software should

behave


29/30

31

Activities Common to Software Projects...

Design Deciding how the requirements should be implemented

using the available technology

Includes:

Systems engineering: Deciding what should be inhardware and what in software

Software architecture: Includes dividing the systeminto subsystems and deciding how the subsystemswill interact

Detailed designof the internals of a subsystemUser interface design

Design of databases


30/30

Documents

Purdue CS307 Software Engineering