se-2002 software engineering today - motivation: - software engineering: why? - software...
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SE-2002
SOFTWARE ENGINEERING
• Today - motivation:
- Software Engineering: Why?- Software Engineering: What?
SE-2002
WHY SOFTWARE ENGINEERING?
• High failure rate of software projects.• Expensive or dramatic failures
- http://www.csc.calpoly.edu/~jdalbey/205/Resources/resources.html has, in addition to an also otherwise good set of links, also links to descriptions of failed software projects.
• Also the partially succesfull software projects have problems.
• A belief that systematic work could improve things.
SE-2002
HOW TO IDENTIFY SOFTWARE PROJECT SUCCESS
• The product is accepted or sells
• Economical profit
• Low error rate
• Schedule and budget are kept
SE-2002
SUCCESS FACTORS
• Good project management• Understanding the needs and freezing the
requirements• Controlled implementation and delivery• Skilled project personnel• Sufficient resources• Good communication between groups
SE-2002
MAJOR ERRORS
• Too optimistic design• Over-emphasizing technology• Management problems• No profitability pre-evaluation• Unrealistic resources• Communication problems
SE-2002
SUCCESS STUDIES - ONNI’88 (Finland)
• Over 100 projects
• Good success: 33%• Questionable: 42%• Failure: 25%
SE-2002
ONNI’88 -REASONS FOR FAILURE
• Inabilities of the Software Engineering personnel
• Insufficient resources
• Management problems
SE-2002
SUCCESS STUDIES:USA’82 - Gibson & Singer
• 18 projects
• Good success: 17%• Partly usable/in use: 28%• Satisfactory (just about?) 11%• Failure: 22%• No evaluation: 11%
SE-2002
USA’82 -REASONS FOR FAILURE
• Organisational problems
• New work methods and salary policies
• Unexpected changes in business
SE-2002
FORSMAN’S STUDIES (FINLAND)
• From Forsman’s book ”ATK-projektin läpivienti”, Suomen ATK-kustannus Oy, 1995
• 17 projects
• Good success: 18%• Partially usable/in use: 29%• Satisfactory (just about?): 29%• Failure: 24%
SE-2002
FORSMAN -REASONS FOR FAILURE
• Problems in organisation and attitudes• The customer could not decide what it wants• Problems with customer and software producer
communication• Inexperience of the software producer
SE-2002
EXAMPLES OF FAILING SOFTWARE RISKS:
• Nuclear war• General technical device malfunction
(e.g. failing life-support devices)• Economical transaction failures• Economical losses in business• Personal tragedies from faulty information• Y2K was considered to imply several different
kinds of risks, but all went reasonably well
SE-2002
A BELIEF IN SYSTEMATIC WORK AND METHODS
• There is no way to guarantee success• Sometimes also the not so good practices seem to
bring some success• However, the studies suggest that the way
software is made is meaningful for the success, at least statistically
• Practical observations support the belief
SE-2002
LARGE SYSTEMS
• Some problems grow with the size of the software, below we give example sizes:
• Dutch KLM airline reservation system (1993), 2 000 000 assembler loc (lines of code)
• Unix System V, relese 4.0 with Xnews and X11, over 3 700 000 loc
• Nokia NMS/2000 network management system, over 2 400 000 loc
• NASA Space Shuttle software, 40 000 000 lines of object code
• IBM OS360: 5000 man years of development
SE-2002
SOFTWARE ENGINEERING - WHAT
• IEEE: Software engineering is the systematic approach to the development, operation, maintenance, and retirement of software
• An earlier definition: Software engineering is the establishment and use of sound engineering principles in order to obtain economically software that is reliable and works efficiently on real machines.
SE-2002
SOFTWARE ENGINEERING - WHAT (observations)
• Software engineering concerns the construction of large programs.
• Mastering complexity is essential.• Regular co-operation between people is an integral
part of the process.• Software evolves.• Software development efficiency is important• The software has to serve its purpose and users.