an introduction to software engineering. objectives to introduce software engineering and to...
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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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22
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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