© Gerald Kotonya and Ian Sommerville 2010 Requirements Validation.
Ch1 Ian Sommerville
Transcript of Ch1 Ian Sommerville
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 1
An Introduction to SoftwareEngineering
(CS 4320)
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 2
Instructor
Ye Duan (321 Engr West)
Interests: Computational Graphics and
Biomedical Imaging
Email: [email protected] Office Hours: Monday 3-5pm
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 3
Malik Al Jarad Tubaishat
Office hours: Monday 2-3pm; Thursday 10-11am
Email: [email protected]
Room: 242 EBWYongjian Xi
Office hours: Monday 1-2pm; Friday 1-2pm
Email: yxry2@mizzou
Room: 242 EBW
Teaching Assistants
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 4
Class Hours: TR 11:00 AM -12:15 PM
Room: Lafferre Hall (EBE) E1419.
(245 EBW on April 12)
Textbook: Software Engineering, by Sommerville,Ian, 7th Edition, Addison Wesley, 2004.
Prerequisites: CS 2050 - Algorithm Design andProgramming II
Home Pages:http://www.cs.missouri.edu/~duan/cs4320.html
Other course info
http://www.cs.missouri.edu/~duan/cs4320.htmlhttp://www.cs.missouri.edu/~duan/cs4320.html -
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Assignments and Exams
Homework: 3 homework assignments throughoutthe semester. These assignments will usually betaken from the exercises at the end of eachchapter in the course textbook.
Exams: There will be two closed-book exams.Class notes will not be allowed during the exams.The format of the exams will be mixed with some
multiple choice, true/false, short answer, anddiagram-based questions.
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Final project - 1
Primary focus of this class (problem-basedlearning)
Students are expected to work together in groups
of 3-4 members and produce a working system
for a real-world client.
The client may be a business, organizations,instructor, friend or relative, so long as they can
provide a list of requirements.
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Students are expected to document their entiresoftware process, demonstrate their finishedproduct, and provide a plan for systemmaintenance and support.
Please see the instructor or teaching assistantsearly in the semester if you are having difficultyfinding a client or other group members.
3 phases
Phase I due on 9/15
Final project - 2
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Phase I report
Team member list
Contact person (for communication withinstructor and TAs)
Project plan (meeting every week) Project description (after talking to users)
Overview
Objectives
Scope
Benefits,
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Grading
Homework assignments 20% (6%, 7%, 7%)
Exam 1 20%
Exam 2 20%
Final Project 40% 10% from peers (students)
15% presentation
15% report
Reduction in score by poor evaluation from other teammembers in the same team.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 10
How to get maximum from your tuition
Attend class regularly
Read the related chapters in the textbook
Do your homework assignment independently
(dont use google) Visit teaching staff whenever you have questions
Work on the final project every week
Think more!
-- schedule
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 11
Objectives
To introduce software engineering and to explainits importance
To set out the answers to key questions aboutsoftware engineering
To introduce ethical and professional issues and
to explain why they are of concern to softwareengineers
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 12
Topics covered
FAQs about software engineering
Professional and ethical responsibility
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 13
Software engineering
The economies of ALL developed nations aredependent on software.
More and more systems are software controlled
Software engineering is concerned with theories,
methods and tools for professional softwaredevelopment.
Expenditure on software represents asignificant fraction of GNP in all developed
countries.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 14
Software costs
Software costs often dominate computer systemcosts. The costs of software on a PC are oftengreater 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 timesdevelopment costs.
Software engineering is concerned with cost-effective software development.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 15
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?
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 16
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?
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 17
What is software?
Computer programs and associated documentation suchas requirements, design models and user manuals.
Software products may be developed for a particularcustomer or may be developed for a general market.
Software products may be Generic - developed to be sold to a range of different customers
e.g. PC software such as Excel or Word.
Custom - developed for a single customer according to theirspecification.
New software can be created by developing new
programs, configuring generic software systems orreusing existing software.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 18
What is software engineering?
Software engineering is an engineering disciplinethat is concerned with all aspects of softwareproduction.
Software engineers should adopt a systematic
and organised approach to their work and useappropriate tools and techniques depending onthe problem to be solved, the development
constraints and the resources available.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 19
What is the difference between softwareengineering and computer science?
Computer science is concerned with theory andfundamentals; software engineering is concernedwith the practicalities of developing anddelivering useful software.
Computer science theories are still insufficient toact as a complete underpinning for softwareengineering (unlike e.g. physics and electrical
engineering).
Wh i h diff b f
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 20
What is the difference between softwareengineering and system engineering?
System engineering is concerned with allaspects of computer-based systemsdevelopment including hardware, software andprocess engineering. Software engineering is
part of this process concerned with developingthe software infrastructure, control, applicationsand databases in the system.
System engineers are involved in systemspecification, architectural design, integrationand deployment.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 21
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 thecustomer wants
Evolution - changing the software in response to
changing demands.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 22
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;
Iterative development;
Component-based software engineering.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 23
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 systemattributes such as performance and systemreliability.
Distribution of costs depends on the
development model that is used.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 24
Activity cost distributionWat erfall model
Iterative development
Component-based software eng ineering
Development and evolution costs for long-lifetime syst ems
Syst em evolu tion
10 200 30 4000
Syst em develop ment
Sp eci fi cat io n Desi gn Develo pment Int eg rat ion and t es tin g
25 50 75 1000
Specification Development Integ ration and testing
2 5 50 75 1000
Specification Iterative d evelopmen t System testing
2 5 50 75 1000
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 25
Product development costs
Specification Developmen t System testing
25 50 75 1000
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 26
What are software engineering methods?
Structured approaches to software development whichinclude system models, notations, rules, design adviceand 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
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 27
What is CASE (Computer-Aided SoftwareEngineering)
Software systems that are intended to provide automatedsupport for software process activities.
CASE systems are often used for method support.
Upper-CASE
Tools to support the early process activities of requirementsand design;
Lower-CASE
Tools to support later activities such as programming,debugging and testing.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 28
What are the attributes of good software?
The software should deliver the required functionality andperformance 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 compatiblewith other systems.
What are the key challenges facing software
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 29
What are the key challenges facing softwareengineering?
Heterogeneity, delivery and trust.
Heterogeneity
Developing techniques for building software that can cope withheterogeneous platforms and execution environments;
Delivery Developing techniques that lead to faster delivery of software;
Trust
Developing techniques that demonstrate that software can betrusted by its users.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 30
Professional and ethical responsibility
Software engineering involves widerresponsibilities than simply the application oftechnical skills.
Software engineers must behave in an honest
and ethically responsible way if they are to berespected as professionals.
Ethical behaviour is more than simply upholdingthe law.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 31
Issues of professional responsibility
Confidentiality Engineers should normally respect the confidentiality
of their employers or clients irrespective of whetheror not a formal confidentiality agreement has beensigned.
Competence Engineers should not misrepresent their level of
competence. They should not knowingly accept workwhich is outwith their competence.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 32
Issues of professional responsibility
Intellectual property rights Engineers should be aware of local laws governing the use of
intellectual property such as patents, copyright, etc. Theyshould be careful to ensure that the intellectual property ofemployers 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 an employers machine,
say) to extremely serious (dissemination of viruses).
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 33
ACM/IEEE Code of Ethics
The professional societies in the US havecooperated to produce a code of ethical practice.
Members of these organisations sign up to thecode of practice when they join.
The Code contains eight Principles related to thebehaviour of and decisions made by professionalsoftware engineers, including practitioners,educators, managers, supervisors and policymakers, as well as trainees and students of theprofession.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 34
Code of ethics - preamble
Preamble The short version of the code summarizes aspirations at a high
level of the abstraction; the clauses that are included in the fullversion give examples and details of how these aspirationschange the way we act as software engineering professionals.Without the aspirations, the details can become legalistic and
tedious; without the details, the aspirations can become highsounding but empty; together, the aspirations and the detailsform a cohesive code.
Software engineers shall commit themselves to making theanalysis, specification, design, development, testing andmaintenance of software a beneficial and respected profession.
In accordance with their commitment to the health, safety andwelfare of the public, software engineers shall adhere to thefollowing Eight Principles:
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 35
Code of ethics - principles
PUBLIC Software engineers shall act consistently with the public
interest.
CLIENT AND EMPLOYER
Software engineers shall act in a manner that is in the best
interests of their client and employer consistent with the publicinterest.
PRODUCT
Software engineers shall ensure that their products and relatedmodifications meet the highest professional standards possible.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 36
Code of ethics - principles
JUDGMENT Software engineers shall maintain integrity and independence
in their professional judgment.
MANAGEMENT
Software engineering managers and leaders shall subscribe to
and promote an ethical approach to the management ofsoftware development and maintenance.
PROFESSION
Software engineers shall advance the integrity and reputation ofthe profession consistent with the public interest.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 37
Code of ethics - principles
COLLEAGUES Software engineers shall be fair to and supportive of
their colleagues.
SELF
Software engineers shall participate in lifelonglearning regarding the practice of their professionand shall promote an ethical approach to the practiceof the profession.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 38
Ethical dilemmas
Disagreement in principle with the policies ofsenior management.
Your employer acts in an unethical way andreleases a safety-critical system without finishing
the testing of the system.
Participation in the development of militaryweapons systems or nuclear systems.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 39
Key points
Software engineering is an engineering discipline that isconcerned with all aspects of software production.
Software products consist of developed programs andassociated documentation. Essential product attributesare maintainability, dependability, efficiency and usability.
The software process consists of activities that areinvolved in developing software products. Basic activitiesare software specification, development, validation andevolution.
Methods are organised ways of producing software. They
include suggestions for the process to be followed, thenotations to be used, rules governing the systemdescriptions which are produced and design guidelines.
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Ian Sommerville 2004 Software Engineering, 7th edition. Chapter 1 Slide 40
Key points
CASE tools are software systems which are designed tosupport routine activities in the software process such asediting design diagrams, checking diagram consistencyand keeping track of program tests which have been run.
Software engineers have responsibilities to theengineering profession and society. They should notsimply be concerned with technical issues.
Professional societies publish codes of conduct which setout the standards of behaviour expected of their
members.