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 - urces.html has, in addition to an also otherwise good set of links, also links to descriptions of failed software projects. urces.html 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, 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), assembler loc (lines of code) Unix System V, relese 4.0 with Xnews and X11, over loc Nokia NMS/2000 network management system, over loc NASA Space Shuttle software, 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.