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Software Engineering, 2006 Introduction 1

Software Engineer ing

Introduction

Mira Balaban

Department of Computer Science

Ben-Gurion university

Based on slides of Igor Potapov: http://www.csc.liv.ac.uk/~igor/COMP201

Ian Sommerville:http://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.html

Alexander Borgida: http://www.cs.rutgers.edu/~borgida/431/

http://www.csc.liv.ac.uk/~igor/COMP201http://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.htmlhttp://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.htmlhttp://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.htmlhttp://www.comp.lancs.ac.uk/computing/resources/IanS/SE7/Presentations/index.htmlhttp://www.csc.liv.ac.uk/~igor/COMP201http://www.csc.liv.ac.uk/~igor/COMP201

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Software Engineering, 2006 Introduction 2

What is software?

Computer programsand associated documentation

Software productsmay be developed for a particularcustomer or may be developed for a general market

Software productsmay be

Generic- developed to be sold to a range of differentcustomers

Bespoke(custom) - developed for a single customeraccording to their specification

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Software Engineering, 2006 Introduction 3

What is Engineering?

Application of a systematic, disciplined,

quantifiable approach to

structures,machines,

products,

systems,

processes.

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Software Engineering, 2006 Introduction 4

What is Software Engineering?

That form of engineering that applies a systematic disciplined quantifiable approach

the principles of computer science, design, engineering, management,mathematics, psychology, sociology, and other disciplines as necessary

and sometimes just plain invention

to creating, developing, operating and maintaining costeffective,

reliably correct, high-quality solutions tosoftware problems[Berry 92]

SE requires the identification of a problem, a computer to carryexecute a software product, and a user environment (composed

of people, tools, methodologies, etc.)

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The task of software engineers?

Software engineersshould

adopt a systematic and organised approach to their work

use appropriate tools and techniquesdepending on the problem to be solved,

the development constraints and

the resources available

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Software Engineering, 2006 Introduction 6

Origin of Software Engineering?

Software engineering deals with the development ofhigh-quality software systems.

Software engineering isabstractno physicallimitations:

leads tounlimited complexity.

Software engineeringcoined in 1968: withindiscussion of software crisis.

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Software Engineering, 2006 Introduction 7

What is the software crisis?

Major projects are meaningfully late.

Software costs more than predicted.

Software is unreliable.

Software is difficult to maintain. Poor performance.

While hardware costs were decreasing, softwarecosts were rising.

requires techniques to control thecomplexity of large software systems.

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Software Engineering, 2006 Introduction 8

Why Software Engineering is Needed?

Software development is hard!

Important to distinguish easy systems(onedeveloper, one user, experimental use only) fromhard systems (multiple developers, multiple users,

products).

Experience with easy systems is misleading:

One person techniques do not scale up.

Analogy with bridge building:

Over a stream= easy, one person job.

Over a big River ? (the techniques do not scale)

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Software Engineering, 2006 Introduction 9

Why is SE hard?

Different kinds of problems: we are used to problems where there are pre-stated specifications

(e.g. ,write a program to find the shortest path...), where it makessense to talk about the correctness of a solution

real world problems: (e.g., software to help people controlnuclear reactors): acceptability is defined by user satisfaction(validation vs verification). Implies evolut ion is intrinsic

wicked problems:

define and solve concurrently

no unique definition or solution always room for improvement in defn and soln

new problem, not previously encountered

many stakeholders, with different goals

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Software Engineering, 2006 Introduction 10

Essential Difficulties of SE: [Brooks]

COMPLEXITY: software is more complex for its size than any other human construct;

no two parts are alike (vs. car, microchips,...);

science advances by simplifying, while software cannot ignore/simplify details of real world

CONFORMITY:

among {hardware, software, people, organizations} it is software which is chosen to bend oradaptbecause it is more malleable, last to arrive on the scene, usually only one developed onsite,...

CHANGEABILITY: once delivered, most engineered products (hardware, cars, buildings) are rarely changed because

the cost to change would be a large fraction of the cost to make. The (unfortunate)perceptionis that software is cheap to change. And pressure to change comes from successful use, and

aging hardware platform. INVISIBILITY: since it has no physical reality, software is not properly visualizable with diagrams, etc. in the

way in which houses, circuits, etc are.

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Why Software Engineering Is Hard?

The main problem is complexity

Many sources, but sizeis key:

UNIXcontains 4 million linesof codeWindows 2000contains 108linesof code

Software engineering is about managingthis complexity.

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Software Engineering, 2006 Introduction 12

What will (not) make a big difference: [Brooks1987]

Minor Ada or Java or C# or Python or ...

Object-Oriented Programming

Artificial Intelligence

Automatic Programming

Graphical programming Program verification

Environments and tools

Workstations

Major Buy vs build

Requirements refinement and prototyping

Incremental development

Great designers (Unix, Pascal,Smalltalk vs Cobol,PL/I.Ada,MS-DOS)

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Software Engineering, 2006 Introduction 13

Software engineeringas a discipline

withincomputer science

Computer Science Software Engineering

is concerned with

Computer science theoriesare currently insufficient to act asa complete underpinning for software engineering, BUT it is

a foundation for practical aspects of software engineering

theory

fundamentals

the practicalities of developing

delivering useful software

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Software Engineering, 2006 Introduction 14

What is the differencebetween software

engineering and system engineering?

Software engineeringis part of System engineering

System engineeringis concerned with all aspects ofcomputer-based systems development including

hardware,

softwareand

process engineering

System engineersare involved in

systemspecification,

architectural design,

integrationand deployment

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Software Engineering, 2006 Introduction 15

SE: Processes, Models, and Tools

Processes:

Systematic ways of organizing teams and tasks so that there is a clear, traceablepath from customer requirements to the final product. (e.g.,:Waterfall,Prototyping, Spiral etc.) Processes help organize and co-ordinate teams, preparedocumentation, reduce bugs, manage risk, increase productivity, etc.

Models:

Well-defined formal or informal languages and techniques for organizing andcommunicating arguments and decisions about software. e.g:specification languages (Z, etc),

design models (UML, etc)

Models help stake-holders communicate: customers with developers, designersand developers, developers and testers etc. If they are formal, they also can helpsupport automation

Tools:

Programs which automate or otherwise support software development tasks: e.g.,

Eclipse, Make, CVS, etc.

Tools increase productivity, quality and can reduce costs

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Software Engineering, 2006 Introduction 16

Software Engineering Activities

1. Problem statement needs analysis

requirements specification: functional, non-functional

2. Design architectural

detailed

(communication, database)3. Implementation

coding

testing:

module

integration

documentation

4. Maintenance corrective

adaptive

enhancement

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What is asoftware process?

A set of activitieswhose goal is thedevelopment or evolution of software.

Generic activities in all software processes are:

Specification- what the system should do and itsdevelopment constraints.

Development-production of the software system

Validation- checking that the software is what the

customer wants.Evolution- changing the software in response to

changing demands.

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Software Engineering, 2006 Introduction 18

What is a software process model?

An abstraction of a software process, presented from a specificperspective.

Examples of process perspectives:Workflow perspective represents inputs, outputs and dependencies.

Data-flow perspective represents data transformation activities.Role/action perspectiverepresents the roles/activities of thepeople involved in software process.

Generic process models: Waterfall

Iterative development Formal transformation

Integration from reusable components

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Software Engineering, 2006 Introduction 20

What isCASE?

(Computer-Aided Software Engineering)

Upper-CASE

Tools to support the early processactivities of requirements and design.

Lower-CASETools to support activities such as programming,

debugging and testing.

Software systems which are intended to provideautomated support for software process activities, suchas requirements analysis, system modelling, debuggingand testing.

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What are the attributes of good software?

Maintainability

Software must evolve to meet changing needs.

Dependability

Software must be trustworthy.

Efficiency

Software should not make wasteful use of system resources.

Usability

Software must be usable by the users for which it was designed.

The software should deliver the required functionalityand performance to the user and should be

maintainable, dependable, efficientand usable

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Software Engineering, 2006 Introduction 22

What are the key challenges

facing software engineering?

Software engineering in the 21stcentury faces threekey challenges:

Heterogeneity

Systems are distributed and include a mix of hardware and software.

Legacy systems (old valuable systems) must be maintained, updatedand integrated into new systems.

Delivery

There is an increasing pressure

for faster delivery of software. Trust

Software must be trusted by its nave users.

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Software Engineering, 2006 Introduction 23

Professional and ethical responsibi l i ty (1)

Software engineering involves wider

responsibilities than simply the application of

technical skills.

Software engineers must behave in an honest

and ethically responsible way if they are to be

respected as professionals.

Ethical behaviour is more than simplyupholding the law.

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I ssues of professional responsibil i ty (2)

Confidentiality

Engineers should normally respect theconfidentiality of their employers or clients

irrespective of whether or not a formalconfidentiality agreement has been signed.

Competence

Engineers should not misrepresent their level of

competence. They should not knowingly acceptwork which is out with their competence.

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I ssues of professional responsibil i ty (3)

Intellectual property rights

Engineers should be aware of local laws governing the use

of intellectual property such as patents, copyright, etc.

They should be careful to ensure that the intellectual

property of employers and clients is protected. Computer misuse

Software engineers should not use their technical skills to

misuse other peoples computers. Computer misuse

ranges from relatively trivial (game playing on anemployers machine, say) to extremely serious

(dissemination of viruses).

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Software Engineering, 2006 Introduction 26

ACM /IEEE Code of Ethics

The professional societies in the US have cooperatedto produce a code of ethical practice.

Members of these organisations sign up to the code of

practice when they join. The Code contains eight Principles related to the

behaviour of and decisions made by professionalsoftware engineers, including practitioners, educators,managers, supervisors and policy makers, as well astrainees and students of the profession.

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Code of ethics - principles

1. PUBLIC Software engineers shall act consistently with the public

interest.

2. CLIENT AND EMPLOYER

Software engineers shall act in a manner that is in the bestinterests of their client and employer consistent with the

public interest.

3. PRODUCT

Software engineers shall ensure that their products andrelated modifications meet the highest professional

standards possible.

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Code of ethics - principles

4. JUDGMENT

Software engineers shall maintain integrity and independence

in their professional judgment.

5. MANAGEMENT

Software engineering managers and leaders shall subscribe to

and promote an ethical approach to the management of

software development and maintenance.

6. PROFESSION

Software engineers shall advance the integrity and reputationof the profession consistent with the public interest.

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Code of ethics - principles

7. COLLEAGUES

Software engineers shall be fair to and supportive

of their colleagues.

8. SELF

Software engineers shall participate in lifelong

learning regarding the practice of their profession

and shall promote an ethical approach to thepractice of the profession.

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Ethical di lemmas

Disagreement in principle with the policies of

senior management.

Your employer acts in an unethical way and

releases a safety-critical system without

finishing the testing of the system.

Participation in the development of military

weapons systems or nuclear systems.

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Summary: Key points (1)

Software engineering is an engineering discipline that isconcerned with all aspects of software production.

Software products consist of developed programs andassociated documentation. Essential product attributes are

maintainability, dependability, efficiency and usability. The software process consists of activities that are involved in

developing software products. Basic activities are softwarespecification, development, validation and evolution.

Methods are organised ways of producing software. They

include suggestions for the process to be followed, thenotations to be used, rules governing the system descriptionswhich are produced and design guidelines.

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Summary: Key points (2)

CASE tools are software systems which are designed to

support routine activities in the software process such as

editing design diagrams, checking diagram consistency and

keeping track of program tests which have been run.

Software engineers have responsibilities to the engineering

profession and society. They should not simply be concerned

with technical issues.

Professional societies publish codes of conduct which set out

the standards of behaviour expected of their members.