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Software engineering (2IP25) Software engineering (2IP25)

Prof.dr. Mark van den Brand

Practical issues

• Docent:

P f d M k d B d ( j d b d@t l) HG5 59

• Prof.dr. Mark van den Brand (m.g.j.v.d.brand@tue.nl), HG5.59
• Meer informatie over SE (2IP25):
• http://www win tue nl/~mvdbrand/courses/se/0910/
• http://www.win.tue.nl/~mvdbrand/courses/se/0910/

− slides − opdrachten − achtergrond artikelen g

• boek (verplicht):

− Software Engineering van Hans van Vliet, 3de editie, Wiley

/ Faculteit Wiskunde en Informatica

PAGE 1 3-2-2010

Practical issues

• Examen:
• Schriftelijk examen (70%)

− Materiaal: lid − slides − artikelen − boek boe

• Praktische opgave: analyseren van URD (30%)

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Why Software Engineering in general?

• The nature of software …
• Software is everywhere

− dependable − robust

• Software is intangible

− hard to understand development effort

• Software is easy to reproduce

− cost is in its development − in other engineering products, manufacturing is the costly stage

• The industry is labor-intensive

− hard to automate

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Why Software Engineering?

• The nature of software …
• Untrained people can hack something together

− quality problems are hard to notice S ft i t dif

• Software is easy to modify

− people make changes without fully understanding it

• Software does not ‘wear out’

So t a e does

• t

ea out − it deteriorates by having its design changed: − erroneously, or − in ways that were not anticipated, thus making it complex

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Why Software Engineering?

• The nature of software …
• Conclusions

− Much software has poor design and is getting worse D d f ft i hi h d i i − Demand for software is high and rising − We are in an ever lasting ‘software crisis’ − We have to learn to ‘engineer’ software e a e to ea to e g ee so t a e

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Why Software Engineering?

• Types of software …

y

• Custom

− For a specific customer G i

• Generic

− Sold on open market − Often called O te ca ed − COTS (Commercial Off The Shelf) − Shrink-wrapped

• Embedded

− Built into hardware − Hard to change

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Hard to change

Why Software Engineering?

• Within 30 years the amount of software in cars went

y from 0 lines of code to more than 10,000,000 lines of code

• More than 2000 functions are controlled by software
• More than 2000 functions are controlled by software

in high-end cars

• 50/70% of the development costs of hard/software

p are software costs

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Why Software Engineering?

• Embedded Software as Innovation Driver
• Software is today the most crucial innovation driver for

technical systems, in general

• By software
• By software

− we realize innovative functions, − we find new ways of implementing known functions with reduced costs, less weight or higher quality, − we save energy and, what is, in particular, important, − we combine functions and correlate them into multi- − we combine functions and correlate them into multi- functional systems

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What is Software Engineering?

• Software engineering is the establishment and use
• f sound engineering principles in order to obtain
• f sound engineering principles in order to obtain

economically software that is reliable and works efficiently on real machines

• Other definitions:
• The process of solving customers’ problems by the systematic
• The process of solving customers problems by the systematic

development and evolution of large, high-quality software systems within cost, time and other constraints

• IEEE: (1) the application of a systematic, disciplined, quantifiable

( ) pp y , p , q approach to the development, operation, maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1).

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What is Software Engineering?

• Software engineering concerns the development of

large programs large programs

• Moving from programming-in-the-small to programming-in-

the-large

• Mastering complexity
• Evolution

Effi i f ft d l t

• Efficiency of software development
• Cooperation between people is an integrated part
• f programming-in-the-large

p g g g

• Software has to supports its users effectively
• …

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What is Software Engineering?

• Solving customers’ problems

g

• This is the goal of software engineering
• Sometimes the solution is to buy, not build

Addi f t d t h l l th

• Adding unnecessary features does not help solve the

problem

• Software engineers must communicate effectively to

identify and understand the problem

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What is Software Engineering?

• Systematic development and evolution

y

• An engineering process involves applying well

understood techniques in an organized and disciplined way way

• Many well-accepted practices have been formally

standardized b h IEEE ISO − e.g. by the IEEE or ISO

• Most development work is evolution

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What is Software Engineering?

• Large, high quality software systems
• Software engineering techniques are needed because
• Software engineering techniques are needed because

large systems cannot be completely understood by

• ne person
• Identification of missing quality aspects before

building

• Teamwork and co-ordination are required

q

• Key challenge: dividing up the work and ensuring that

the parts of the system work properly together

• The end product must be of high quality
• The end-product must be of high quality

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What is Software Engineering?

• Cost, time and other constraints
• Finite resources
• The benefit must outweigh the cost
• Others are competing to do the job cheaper and faster
• Inaccurate estimates of cost and time have caused many

project failures

• Quality attributes:
• Usability, efficiency, reliability, maintainability, reusability
• The different qualities can conflict

− increasing efficiency can reduce maintainability − increasing usability can reduce efficiency

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Stakeholders in Software engineering

• 1. Users
• Those who use the software
• 2. Customers
• Those who pay for the software
• 3. Software developers

4 Development Managers

• 4. Development Managers

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Software Quality...

• Usability
• Users can learn it and fast and get their job done easily
• Users can learn it and fast and get their job done easily
• Efficiency
• It doesn’t waste resources such as CPU time and memory
• Reliability
• It does what it is required to do without failing

M i t i bilit

• Maintainability
• It can be easily changed
• Reusability
• Its parts can be used in other projects, so reprogramming

is not needed

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Software Quality and the Stakeholders

User:

easy to learn;

Customer:

solves problems at an acceptable cost in efficient to use; helps get work done an acceptable cost in terms of money paid and resources used QUALITY SOFTWARE

Developer:

easy to design;

Development manager:

sells more and pleases customers easy to maintain; easy to reuse its parts pleases customers while costing less to develop and maintain

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Software Quality: Conflicts and Objectives Objectives

• The different qualities can conflict
• Increasing efficiency can reduce maintainability or

reusability

• Increasing usability can reduce efficiency

g y y

• Setting objectives for quality is a key engineering

activity

• You then design to meet the objectives
• Avoids ‘over-engineering’ which wastes money

O ti i i i l ti

• Optimizing is also sometimes necessary
• E.g. obtain the highest possible reliability using a fixed

budget

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