2.SommerVilleCh01

7/28/2019 2.SommerVilleCh01

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Introduction to Software Engineering Kamran Sartipi

Programming is part ofSoftware Design & Engineering

These slides introduce software engineering andexplain its importance in dealing with largesoftware systems.

Provide answers to key questions about softwaredesign and development as part of software

engineering discipline.


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Software systems

The impact of software systems on modern society andtechnology for 50 years. Process automation: automobile industry; refinery; software

product family for electronic devices; telephony and switching

systems Equipment control: embedded systems in different electronic

devices such as home appliances; automobile control gadgets Scientific problems: differential equations; matrix operations;

model checking; searching algorithms; information system

manipulation Entertainment industry: gaming; graphics; movies; music Education and office management: distance education; word

processors; databases; spreadsheets; slide presenters


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Software systems

Example of very large software systems Flight simulators; medical and imaging applications; air-traffic

control; banking; telecommunications; etc. These systems are written in more than 500 different languages. Billions of lines of source code are written for mission critical

software systems worldwide.


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Software engineering to solve

software crisis

Software crisis refers to the current state of softwaretechnology in dealing with development and maintenanceof large and complex software systems. Instances are:

For every 8 large projects, 2 are cancelled. Most projects exceed their time-schedule by 50%. 75% of large software systems malfunction after completion. Detecting and correcting errors take 50% of time and effort. Maintenance cost of a system is 60% of entire cost. An example: baggage-handling system at Denver international airport

4000 telecars, 5000 electric-eyes, 400 radio receivers, 100 computers, cost $193million

Software engineering tackles the software crisis by providingdisciplined processes and methodologies to design,implement, and maintain large systems.


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Software engineering key questions

What is software? What is software engineering? What is the difference between softwareengineering and computer science? What is the difference between software

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


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Software engineering

What are the costs of software engineering? What are software engineering methods? What is CASE (Computer-Aided SoftwareEngineering) What are the attributes of good software? What are the key challenges facing software

engineering?


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What is software?

Computer programs and associateddocumentation: SRS, SDS, Technical manual, User manual, Source code,

Binary files, Build files, Versions Tool provided documents: Reverse Engineering aspects,

Tracing code to requirement Software products may be

Generic - developed to be sold to a range of different customers Customized - developed for a single customer according to their

specification


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What is software engineering?

Multi-person construction of multi-versionsoftware [Parnas 1978]

Software engineering is an engineering discipline whichis concerned with all aspects of software production

Software engineers should adopt a systematic andorganised approach to their work and use appropriate

tools and techniques depending on the problem to besolved, the development constraints and the resourcesavailable


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Professional Responsibilities ofSoftware Engineers

Accept individual responsibility Solve the real problem Be honest about capabilities and competence Produce reviewable designs Consider maintainability of product Respect to confidentiality of the clients Knowledge of IP rights for patents, copyright, etc. No computer miss-use by e.g., computer games;

spreading computer viruses P.Eng. Applicants write Ethics and Law Exams


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What is the difference between softwareengineering and computer science?

Computer science is concerned with theory andfundamentals; software engineering is concernedwith the practicalities of developing and

delivering useful software Computer science theories are currently

insufficient to act as a complete underpinning for

software engineering


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What is the difference between softwareengineering and system engineering?

System engineering is concerned with all aspectsof computer-based systems developmentincluding hardware, software and process

engineering. Software engineering is part of thisprocess

System engineers are involved in systemspecification, architectural design, integration and

deployment


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What is a software process?

A set of activities whose goal is the developmentor 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 system Validation - checking that the software is what the customer

wants Evolution - changing the software in response to changing

demands


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What is a software process model?

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

Examples of process perspectives are Workflow perspective - sequence of activities Data-flow perspective - information flow Role/action perspective - who does what

Generic process models Waterfall Evolutionary development Formal transformation Integration from reusable components


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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 beingdeveloped and the requirements of system

attributes such as performance and system

reliability Distribution of costs depends on the development

model that is used


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What are software engineering methods?

Structured approaches to software development whichinclude system models, notations, rules, design advice andprocess 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


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What is CASE (Computer-AidedSoftware Engineering)

Software systems which are intended to provideautomated 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-CASE

Tools to support later activities such as programming,debugging and testing


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What are the attributes of good software?

The software should deliver the required functionality andperformance to the user and should be maintainable,dependable and usable

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


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What are the key challenges facingsoftware engineering?

Coping with legacy systems, coping withincreasing diversity and coping with demands forreduced delivery times Legacy systems

Old, valuable systems must be maintained and updated Heterogeneity

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

There is increasing pressure for faster delivery of software

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