Software Engineering

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Software Engineering

Sheng Bin

Shanghai Jiao Tong University

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Software Engineering

Course Information Teacher:

Bin Sheng( 盛斌 )

SEIEE3-511, 15026790946, shengbin@cs.sjtu.edu.cn

Teaching Assistant:

Li XIA( 夏立 ) ziggzagg@sjtu.edu.cn

Project Mentors:

樊增智谯从彬夏立杜皓殷本俊裴树炜 Course Website:

http://www.cs.sjtu.edu.cn/~shengbin/course/SE/sesite/home.html

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Course Overview

Part A: Software Engineering Concepts

2. Software Life-Cycle Models 3. The Software Process

4. Teams

5. The Tools of the Trade 6. Testing

7. From Modules to Objects 8. Reusability and Portability 9. Planning and Estimating

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Course Overview

Part B: The Workflows of the Software Life Cycle

10. Key Material from Part A 11. Requirements

12. Classical Analysis

13. Object-Oriented Analysis 14. Design

15. Implementation

16. Postdelivery Maintenance 17. More on UML

18. Emerging Technologies

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Team Projects Form teams of 3 (± 1?) students DEADLINE: Sept 28, 2014

After that, teams assigned randomly Project Ideas:

Pls refer to the project presentation ppt.

No more than two (2) groups working on the same pr oject

One (1) new project allowed

• Email your project idea ASAP, before proposal is due, fo r feedback.

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Project Deliverables

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Item Due date

Software Engineeri

ng

1. Proposal Sept 28

2. First report (Specification only)

• Part 1 (Statement of Work & Requirements) • Part 2 (Functional Requirements Spec & UI) • Full Report #1

Oct 31 Oct 31 Oct 31 3. Second report (Design only)

• Part 1 (Interaction Diagrams)

• Part 2 (Class Diagram and System Architecture) • Full Report #2

Dec 1 Dec 8 Dec 15

4. First demo Dec 2 ..

SE Practice

5. Third report (All reports collated) Dec 27

6. final demo Dec 31 ...

7. Electronic Project Archive Dec 3

Assignment + Attendance= 30%

Project=70%

Each group will have a mentor to guide the development of the project.

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Reference book:

1. Stephen R Schach, Object Oriented And Classical Software Engineering 8th Edition, McGraw-Hill.

2. Bruegge & Dutoit: Object-Oriented Software Engineering, Using UML, Patterns and Java, Third Edition, Prentice Hall, 2010.

3. Sommerville, Ian: Software Engineering,9^th Edition, Addison Wesley.

4. Miles & Hamilton: Learning UML 2.0, O’Reilly Media, 2006. ISBN: 0- 596-00982-8

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Why should we learn SE ？ Why should we learn SE?

• Because you are from Computer Science

• SE is the best jobs

• best job of 2011, Career Cast

Best Jobs in America 1. Software engineer 2. College professor 3. Financial advisor

4. Human resources manager 5. Physician assistant

6. Market research analyst 7. Computer/IT analyst 8. Real estate appraiser 9. Pharmacist

10. Psychologist

Money Magazine recently published

"Best Jobs in America"

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Source: US Department of Labor/Bureau of Labor Statistics (Occupational Employment Surveys)

According to the BLS, software engineering unemployment was 4.6% in 2010, compared to 5.4% for electrical engineers.

Average Annual Wages

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Software

Q : If you have to write a 10,000 line program in C to solve a problem, how long will it take?

Answers: generally range from 2-4 months Let us analyze the productivity

• Productivity = output/input resources

• In SW output is considered as LOC

• Input resources is effort - person months; overhea d cost modeled in rate for person month

• Though not perfect, some productivity measure is needed, as project has to keep it high

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Software …

The productivity is 2.5-5 KLOC/PM

Q: What is the productivity in a typical commercial SW organization ?

A: Between 100 to 2000 LOC/PM

Q: Why is it low, when your productivity is so high?

(people like you work in the industry)

A: What the student is building and what the indust ry builds are two different things

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Software…

Students build: student software

Industry builds: industrial strength Systems What is the difference between

• student software and

• industrial strength software

for the same problem?

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Software…

Student

Developer is the use r

• Works for the typical case most of the tim e

• Bugs are tolerable

• UI not important

• No documentation

Industrial Strength Others are the users

• Works robustly

• Bugs not tolerated

• UI very important iss ue

• Documents needed f or the user as well as for the organization a nd the project

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Software…

Student

SW not in critical use Reliability, robustness not important

No investment

Don’t care about port ability

Industrial Strength Supports important fu nctions / business

Reliability , robustnes s are very important Heavy investment

Portability is a key iss ue here

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Industrial Strength Software

Student programs != industrial strength softwa re

Key difference is in quality (including usability, reliability, portability, etc.)

• High quality requires heavy testing, which consum es 30-50% of total development effort

• Requires development be broken in stages such t hat bugs can be detected in each

• Good UI, backup, fault-tolerance, following of stds etc all increase the size for the same functionality

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Industrial strength software

If 1/5^th productivity, and increase in size by a fac tor of 2, industrial strength software will take 10 times effort

Brooks thumb-rule: Industrial strength SW cos ts 10 time more than student SW

In this course, software == industrial strength so ftware

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What is software?

Computer programs and associated docu mentation

Software products may be developed for a p articular customer or may be developed for a general market

Software products may be

• Generic - developed to be sold to a range of differ ent customers

• Bespoke (custom) - developed for a single custo mer according to their specification

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Software is Expensive



Rough cost estimate…

 Productivity = 500 LOC/PM

 Cost to the company = $10K/PM

 Cost per LOC = $20

 So each line of delivered code costs about $20.



A simple application for a business may have 2 0KLOC to 50KLOC

 Cost = $100K to $1Million

 Can easily run on $10K-$20K hardware

 So HW costs <<< SW costs.

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Software is Expensive…

The HW/SW ratio for a computer system has shown a reversal from the early years.

• In 50s , HW:SW :: 80:20

• In 80s , HW:SW :: 20:80

So, SW is very expensive

• Importance of optimizing HW is not much

• More important to optimize SW

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Software is Complex

Complex  complicated

Complex = composed of many simple parts related to one another

Complicated = not well understood, or explained

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Complexity Example:

Scheduling Fence Construction Tasks

Setting posts [ 3 time units ]

Cutting wood [ 2 time units ]

Painting

[ 5 time units for uncut wood;

4 time units otherwise ] Nailing

[ 2 time units for unpainted;

3 time units otherwise ]

Setting posts  Nailing, Painting Cutting  Nailing

…shortest possible completion time = ?

[  “simple” problem, but hard to solve without a pen and paper ]

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More Complexity

Suppose today is Monday, Sept 9, 2013 What day will be on January 3, 2014?

[ To answer, we need to bring the day names and the day numbers into coordination, and for that we may need again a pen and paper ]

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Late & Unreliable

20-25% of SW projects never complete

• Because after some time they realize that the fina l cost will be much higher

Many companies report “runaways”

• Budget & cost out of control

• Consulting companies to help control them

One defense survey found that 70% of the eq uipment problems are due to SW

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Why is SW Unreliable?

SW failures are different from failures of mecha nical or electrical systems

• In software, failures are not due to aging related pro blems

• Failures occur due to bugs or errors that get introduc ed during development

• The bug that causes a failure typically exists from st art, only manifests later

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Maintenance

Once SW delivered, it enters maintenance phas e

Why is maintenance needed for SW when it do es not wear with age?

• Residual errors requiring corrective maintenance

• Upgrades and environment changes – adaptive mai ntenance

Over SW lifetime, maintenance can cost more t han the development cost of SW

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What is Software Engineering?

Problem domain discussed before, now we discu ss the area of SE

SE (IEEE): systematic approach to developm ent [….] of software

Systematic approach: methodologies and practic es that can be used to solve a problem from prob lem domain

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What is SE?

The SWEBOK Knowledge Areas (KAs) Software requirements

Software design Software construction

Software testing Software maintenance

Software configuration management Software engineering management

Software engineering process

Software engineering tools and methods Software quality

http://www.computer.org/portal/web/swebo k/html/ch1

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Basic Problem

CS3130 SOFTWARE ENGINEERING – Summer 2011

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The Role of Software Engg. (1)

Customer Customer

Programmer A bridge from customer needs to programming implementation

First law of software engineering

Software engineer is willing to learn the problem domain

(problem cannot be solved without understanding it first)

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The Role of Software Engg. (2)

30 Customer:

Requires a computer system to achieve some business goals by user interaction or interaction with the environment

in a specified manner

System-to-be

Software-to-be System-to-be

Software-to-be User

Software Engineer’s task:

To understand how the system-to-be needs to interact with the user or the environment so that customer’s requirement is met and design the software-to-be

Programmer’s task:

To implement the software-to-be designed by the software engineer

Environment

May be the same person

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Second Law of Software Engineering

Software should be written for people first

• ( Computers run software, but hardware quickly becomes outd ated )

• Useful + good software lives log

• To nurture software, people must be able to understand it

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Software Engineering Blueprints



Specifying software problems and solutions is li ke cartoon strip writing



Unfortunately, most of us are not artists, so we will use something less exciting:

UML symbols



^{However …}

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What is software engineering?

Software engineering is an engineering discipline which is concerned with all aspects of software pr oduction

Software engineers should

• adopt a systematic and organised approach to their w ork

• use appropriate tools and techniques depending on

• the problem to be solved,

• the development constraints and

• the resources available

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What is the difference between softwar e engineering and computer science?

Computer Science Software Engineering

is concerned with

Computer science theories are currently insufficient to act as a complete

underpinning for software engineering 

 

 theory

 fundamentals

 the practicalities of developing

 delivering useful software

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Software Engineering Computer Scientist

• Proves theorems about algorithms, designs languages, defines knowl edge representation schemes

• Has infinite time…

Engineer

• Develops a solution for an application-specific problem for a client

• Uses computers & languages, tools, techniques and methods

• Has finite (usually not enough) time…

Software Engineer

• Works in multiple application domains

• Has only 3 months...

• …while changes occurs in requirements and available technology

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What is the difference between softwar e engineering and system engineerin

g?

System engineering is concerned with all aspects of c omputer-based systems development including hardwar e, software and process engineering

Software engineering is part of this process

System engineers are involved in

system specification, architectural design, integ ration and deployment

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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 develop ment constraints

• Development - production of the software system

• Validation - checking that the software is what the custom er wants

• Evolution - changing the software in response to changing demands

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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, evoluti on costs often exceed development costs

Costs vary depending on the type of system bein g developed and the requirements of system attrib utes such as performance and system reliability

Distribution of costs depends on the developme nt model that is used

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What are the attributes of good software?

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 design ed

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

dependable and usable

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What are the key challenges

facing software engineering?

Software engineering in the 21^st century faces three k ey challenges:

Legacy systems

• Old, valuable systems must be maintained and updated

Heterogeneity

• Systems are distributed and include a mix of har dware and software

Delivery

• There is increasing pressure for faster delivery of software

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Professional and ethical responsibility

Software engineering involves wider responsibilitie s than simply the application of technical skills

Software engineers must behave in an honest and e thically responsible way if they are to be respected as professionals

Ethical behaviour is more than simply uphold ing the law

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Thanks

shengbin@cs.sjtu.edu.cn