Software Engineering - Introduction 1 Definition(s) of Software Engineering Establishment and use of sound engineering principles to obtain economically

Software Engineering - Introduction

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Definition(s) of Software Engineering

Establishment and use of sound engineering principles to obtain economically software that is reliable and works on real machines efficiently. (Fritz Bauer)


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Definition(s) of Software Engineering (cont’d)

(i) Application of a systematic, disciplined, quantifiable approach to the development, operation and maintenance of software; that is, the application of engineering to software.

(ii) The study of approaches as in (i). (IEEE 93)


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• By “systematic” we mean:

Following a well-defined sequence of activities,

- in which desired outputs (deliverables) are well-defined

- by using well-defined inputs(i.e. documented syntax, semantics, context and other relevant properties of the input)

- in a well-defined process (e.g. using organizational standards for interprocess communication, data formats, error handling etc.)

- whose outputs are in turn used similarly as inputs in subsequent process(es),

- until the final output is achieved,

- and where the correctness of the output is verifiable. Note: The “inputs” and “outputs” most often refer to requirements, software specifications, the software itself, documentation, test inputs/outputs and similar software artifacts.Back


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By “disciplined” we mean:

• Each process is followed using organizational principles (e.g. who manages whom, who is responsible for what?),

• Intermediate results are carefully documented, as well as final results,

• Actions are traceable as to their causes, individuals involved, time of occurrence and circumstances.

Back


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By “quantifiable” we mean:

• The size and extent of the required effort

(size of output code, data, documentation, manpower, duration, budget for development, expected error rate and user support)

are predictable within justifiable and acceptable bounds


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What SWE is not:

• Just “programming” or “coding”

• System engineering (in a broad sense)although software engineers may be called upon to participate in system engineering analyses

• Software salesmenshipalthough they may be called upon to help analyze customer needs


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Why Do We Need SWE?To make the production of software

• easier • more disciplined and predictable • more economical.

• Back


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Evolution of Software Technology

• Operating systems

• Languages

• Development tools

• Database and networking technology

• Project management tools


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Evolution of machine architecture

• Improvement of machine instruction sets• Invention mass storage devices• Machine interrupt schemes• Much larger physical memories • Virtual memory (paging)• Cache memory• Fault-tolerant computing• Parallel and multi-processing


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Evolution of Systems Interconnection

• Local area networking(peer-to-peer and hierarchical connection, servers)

• Wide area networking(dial-up and fixed connections)

• Networking architecture

• Communication protocols


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Database Systems

• From simple sequential “files” to “databases”

• Indexed files• Hierarchical databases• Network-style databases• Relational databases• More recently, object-oriented

databases• Database management systems


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Decreasing Hardware Costs

• Ever smaller and faster components

• More reliable

• Requiring less energy

• More easily replaceable


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Increasing Demand

• Improved user interfaces

• Cheaper and faster machines

• Increase in application areas

• Improved connections

• Most recently the Internet!


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Differences between Software Engineering and Hardware Engineering

• Software is developed or engineered, not manufactured.

• Software doesn’t wear out (in the usual sense). It is updated or replaced with a new version.

• Most software tends to be custom-builteventhough there is a movement toward component-

based assembly.


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Hardware Failure Pattern“Bathtub Curve”


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Software Failure Pattern


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Examples of Application Areas

• System software

(Operating systems, compilers, databases, graphics packages, communication ...)

• Real-time software

Interacts with external eventsHas tight timing requirementsRequires high-security, reliability and availability Often mission-critical (can not be allowed to fail)


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Application Areas (cont’d)• Business Software

Ranging from simple to very complexRequiring its own expert knowledgeVery large filesNeeds telecommunication, devices like

point-of-sale (POS) terminalsHighly organized computer organization

and personnel (esp. in large companies)

Very detailed records covering long periods


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Engineering and Scientific Software

• Complex formula evaluation

• Very high accuracy

• Interaction with data collection devices(e.g. Sensors) often at high speeds

• High resolution graphic displays of large amounts of data

• Parallel and multi-processor applications


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Embedded Software

• Software embedded in non-computer devices (e.g. cars, planes, cell phones, home appliances such as refrigerators) through special-purpose processors

• Must be resistant to failures, tough climactic conditions, rough handling

• Often optimized to require least memory and still maintain speed


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Military Software

• Often real-time

• Engineering/scientific

• Including embedded components

• High-technology (communications)

• High security and error control (reliability)


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Video Game Software

• Graphic and artistic content

• Video-type action

• Very high timing requirements

• High-sped user interaction

• Graphics and sound integrated


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Artificial Intelligence Software

Involves: Problem solving,

Complex symbolic programming(e.g. pattern recognition, theorem proving, virtual reality concepts, game playing etc.)

Physical system control (e.g. Robotic arm-leg movement)

Vision, sound/voice recognition...


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Web-based Applications

• General public information (news, info about organizations and society)

• Business-to-consumer communication(product promotions, sales)

• Business-to-business communication• Electronic mail• “Surfing”• Seach engines


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QUALITY FOCUS

Methods

Tools

Process

Building Blocks of Software Engineering


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The Generic SWE Approach

• What is the problem to be solved?-- The most important question of all...

-- Do we have sufficient detail ?-- Do we really know what the customer wants?-- Does he agree that that’s what he wants?


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More questions ...

• How will the solution be realized?

How shall we test the solution once it is constructed?

How shall we maintain the system and support the users in the short and long terms?


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The Software Development Process

The Software Development Process (also

called the Software Process) is the process used to answer the above questions, dealing with:

• Definition of the problem• Analysis of the problem• The conception and development of a

design• Implementation of the design

The Software Development Process (cont’d)

• Testing

• Documentation

• User Training (if required)

• Maintenance and support

• Enhancement of the product (if required).


The sequence and extent of activities needed to carry out the above process varies depending on:

• How well the user (customer) understands his own needs

• How well the developers know the application area

Software Process Models 31


• Resources available for the project (time, technology, money, people)

• The type of project (internal/external, level of secrecy, amount of documentation, user support required etc)

• The developer organization

... And many other factors

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Software Engineering - Introduction 1 Definition(s) of Software Engineering Establishment and use of sound engineering principles to obtain economically