An Introduction to Software Engineering

ObjectivesTo introduce software engineering and to

explain its importanceTo set out the answers to key questions

about software engineeringTo introduce ethical and professional issues

and to explain why they are of concern to software engineers

Topics covered

FAQs about software engineeringProfessional and ethical responsibility

Software engineeringThe economies of ALL developed nations are

dependent on software.More and more systems are software

controlledSoftware engineering is concerned with

theories, methods and tools for professional software development.

Expenditure on software represents a significant fraction of GNP in all developed

countries.

Software costsSoftware costs often dominate computer

system costs. The costs of software on a PC are often greater than the hardware cost.

Software costs more to maintain than it does to develop. For systems with a long

life, maintenance costs may be several times development costs.

Software engineering is concerned with cost-effective software development.

FAQs about software engineering

What is software?What is software engineering?What is the difference between software

engineering and computer science?What is the difference between software

engineering and system engineering?What is a software process?What is a software process model?

FAQs about software engineering

What are the costs of software engineering?What are software engineering methods?What is CASE (Computer-Aided Software

Engineering)What are the attributes of good software?What are the key challenges facing software

engineering?

What is software?Computer programs and associated documentation

such as requirements, design models and user manuals.

Software products may be developed for a particular customer or may be developed for a general market.

Software products may beGeneric - developed to be sold to a range of different

customers e.g. PC software such as Excel or Word.Bespoke (custom) - developed for a single customer

according to their specification.New software can be created by developing new

programs, configuring generic software systems or reusing existing software.

What is software engineering?

Software engineering is an engineering discipline that is concerned with all aspects

of software production.Software engineers should adopt a

systematic and organised approach to their work and use appropriate tools and

techniques depending on the problem to be solved, the development constraints and

the resources available.

What is the difference between software engineering and computer science?

Computer science is concerned with theory and fundamentals; software engineering is

concerned with the practicalities of developing and delivering useful software.

Computer science theories are still insufficient to act as a complete

underpinning for software engineering (unlike e.g. physics and electrical

engineering).

What is the difference between software engineering and system engineering?

System engineering is concerned with all aspects of computer-based systems

development including hardware, software and process engineering. Software engineering is part of this process

concerned with developing the software infrastructure, control, applications and

databases in the system.System engineers are involved in system

specification, architectural design, integration and deployment.

What is a software process?A set of activities whose goal is the

development or evolution of software.Generic activities in all software processes are:

Specification - what the system should do and its development constraints

Development - production of the software systemValidation - checking that the software is what the

customer wantsEvolution - changing the software in response to

changing demands.

What is a software process model?

A simplified representation of a software process, presented from a specific perspective.

Examples of process perspectives areWorkflow perspective - sequence of activities;Data-flow perspective - information flow;Role/action perspective - who does what.

Generic process modelsWaterfall;Iterative development;Component-based software engineering.

What are the costs of software engineering?

Roughly 60% of costs are development costs, 40% are testing costs. For custom software,

evolution costs often exceed development costs.Costs vary depending on the type of system

being developed and the requirements of system attributes such as performance and system

reliability.Distribution of costs depends on the

development model that is used.

Activity cost distributionWaterfall model

Iterative development

Component-based software engineering

Development and evolution costs for long-lifetime systems

System evolution

10 200 30 4000

System development

Specification Design Development Integration and testing

25 50 75 1000

Specification Development Integration and testing

25 50 75 1000

Specification Iterative development System testing

25 50 75 1000

Product development costs

Specification Development System testing

25 50 75 1000

What are software engineering methods?

Structured approaches to software development which include system models, notations, rules, design advice and process guidance.Model descriptions

Descriptions of graphical models which should be produced;Rules

Constraints applied to system models;Recommendations

Advice on good design practice;Process guidance

What activities to follow.

What is CASE (Computer-Aided Software Engineering)

Software systems that are intended to provide automated support for software process activities .

CASE systems are often used for method support.Upper-CASE

Tools to support the early process activities of requirements and design;

Lower-CASETools to support later activities such as programming,

debugging and testing.

What are the attributes of good software?

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

maintainable, dependable and acceptable.Maintainability

Software must evolve to meet changing needs;Dependability

Software must be trustworthy;Efficiency

Software should not make wasteful use of system resources;Acceptability

Software must accepted by the users for which it was designed. This means it must be understandable, usable and

compatible with other systems.

What are the key challenges facing software engineering?

Heterogeneity, delivery and trust.Heterogeneity

Developing techniques for building software that can cope with heterogeneous platforms and execution

environments;Delivery

Developing techniques that lead to faster delivery of software;

TrustDeveloping techniques that demonstrate that

software can be trusted by its users.

Professional and ethical responsibility

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 simply upholding the law.

General issues that affect most software

Heterogeneity Increasingly, systems are required to operate as distributed

systems across networks that include different types of computer and mobile devices. (IOS, Android, Symbian).

Business and social change Business and society are changing incredibly quickly as

emerging economies develop and new technologies become available. They need to be able to change their existing software and to rapidly develop new software.

(From symbian to Android and IOS) .!Security and trust

As software is available in all aspects of our lives, it is essential that we can trust that software. (remote software

systems).

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Application typesStand-alone applications

These are application systems that run on a local computer, such as a PC. They include all necessary functionality and do not need to be

connected to a network .Interactive transaction-based applications

Applications that execute on a remote computer and are accessed by users from their own PCs or

terminals. These include web applications. (Online Banking systems, Hotel reservations).

Embedded control systems These are software control systems that control and

manage hardware devices. Examples??

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Application typesBatch processing systems

These are business systems that are designed to process data in large batches. They process large

numbers of individual inputs to create corresponding outputs. Eg. Periodic billing systems, such as phone

billing systems, and salary payment systems.Entertainment systems

These are systems that are primarily for personal use and which are intended to entertain the user .

Systems for modelling and simulationThese are systems that are developed by scientists and

engineers to model physical processes or situations, which include many, separate, interacting objects .

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Application typesData collection systems

These are systems that collect data from their environment using a set of sensors and send

that data to other systems for processing .Systems of systems

These are systems that are composed of a number of other software systems .

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Software engineering fundamentals

Some fundamental principles apply to all types of software system, irrespective of the development

techniques used:Systems should be developed using a managed and

understood development process. Of course, different processes are used for different types of software.

Dependability and performance are important for all types of system .

Understanding and managing the software specification and requirements are important .

Where appropriate, you should reuse software that has already been developed rather than write new

software.

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Software engineering and the web

The Web is now a platform for running application, and organizations are

increasingly developing web-based systems rather than local systems.

Web services allow application functionality to be accessed over the web.

Cloud computing is an approach to the provision of computer services where

applications run remotely on the ‘cloud.’

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1.1 What is Software EngineeringWhere Does the SW Engineer Fit in? (continued)

Relationship between computer science and software engineering

Who Does Software Engineering?

Participants (stakeholders) in a software development project

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System ApproachHardware, software, interaction with peopleIdentify activities and objectsDefine the system boundaryConsider nested systems, systems

interrelationship

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System ApproachThe Element of a System

Activities and objectsAn activity is an event initiated by a triggerObjects or entities are the elements involved

in the activitiesRelationships and the system boundaries

A relationship defines the interaction among entities and activities

System boundaries determine the origin of input and destinations of the output

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Members of the Development Team

Requirement analysts: work with the customers to identify and document the requirementsDesigners: generate a system-level description of what the system is supposed to doProgrammers: write lines of code to implement the designTesters: catch faultsTrainers: show users how to use the systemMaintenance team: fix faults that show up laterLibrarians: prepare and store documents such as software requirementsConfiguration management team: maintain correspondence among various artifacts

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