Practical issues. Why Software Engineering in general? Practical issues. Examen: Schriftelijk examen (70%) Materiaal: artikelen

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1 Practical issues Software engineering (2IP25) Prof.dr. Mark van den Brand Docent: Prof.dr. Mark van den Brand HG Meer informatie over SE (2IP25): win tue nl/~mvdbrand/courses/se/0910/ slides opdrachten achtergrond artikelen boek (verplicht): Software Engineering van Hans van Vliet, 3 de editie, Wiley / Faculteit Wiskunde en Informatica PAGE 1 Practical issues Why Software Engineering in general? Examen: Schriftelijk examen (70%) Materiaal: slides artikelen boek Praktische opgave: analyseren van URD (30%) 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 / Faculteit Wiskunde en Informatica PAGE 2 / Faculteit Wiskunde en Informatica PAGE 3

2 Untrained people can hack something together quality problems are hard to notice Software is easy to modify people make changes without fully understanding it Software does not wear out it deteriorates by having its design changed: erroneously, or in ways that were not anticipated, thus making it complex Conclusions Much software has poor design and is getting worse Demand for software is high h and rising i We are in an ever lasting software crisis We have to learn to engineer ee software / Faculteit Wiskunde en Informatica PAGE 4 / Faculteit Wiskunde en Informatica PAGE 5 Types of software Custom For a specific customer Generic Sold on open market Often Ote called COTS (Commercial Off The Shelf) Shrink-wrapped Embedded Built into hardware Hard to change Within 30 years the amount of software in cars went from 0 lines of code to more than 10,000,000 lines of code More than 2000 functions are controlled by software in high-end cars 50/70% of the development costs of hard/software are software costs / Faculteit Wiskunde en Informatica PAGE 6 / Faculteit Wiskunde en Informatica PAGE 7

3 Embedded Software as Innovation Driver Software is today the most crucial innovation driver for technical systems, in general 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 multifunctional systems 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 Other definitions: 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 approach to the development, operation, maintenance of software; that is, the application of engineering to software. (2) The study of approaches as in (1). / Faculteit Wiskunde en Informatica PAGE 8 / Faculteit Wiskunde en Informatica PAGE 9 Software engineering concerns the development of large programs Moving from programming-in-the-small to programming-inthe-large Mastering complexity Evolution Efficiency i of software development Cooperation between people is an integrated part of programming-in-the-large g g Software has to supports its users effectively Solving customers problems This is the goal of software engineering Sometimes the solution is to buy, not build Adding unnecessary features does not help solve the problem Software engineers must communicate effectively to identify and understand the problem / Faculteit Wiskunde en Informatica PAGE 10 / Faculteit Wiskunde en Informatica PAGE 11

4 Systematic development and evolution An engineering process involves applying well understood techniques in an organized and disciplined way Many well-accepted practices have been formally standardized e.g. by the IEEE or ISO Most development work is evolution Large, high quality software systems Software engineering techniques are needed because large systems cannot be completely understood by one person Identification of missing quality aspects before building Teamwork and co-ordination are required 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 / Faculteit Wiskunde en Informatica PAGE 12 / Faculteit Wiskunde en Informatica PAGE 13 Stakeholders in 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 1. Users Those who use the software 2. Customers Those who pay for the software 3. Software developers 4. Development Managers / Faculteit Wiskunde en Informatica PAGE 14 / Faculteit Wiskunde en Informatica PAGE 15

5 Software Quality... Software Quality and the Stakeholders Usability 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 Maintainability i It can be easily changed Reusability Its parts can be used in other projects, so reprogramming is not needed Customer: solves problems at an acceptable cost in terms of money paid and resources used Developer: easy to design; easy to maintain; easy to reuse its parts QUALITY SOFTWARE User: easy to learn; efficient to use; helps get work done Development manager: sells more and pleases customers while costing less to develop and maintain Software Quality: Conflicts and Objectives The different qualities can conflict Increasing efficiency can reduce maintainability or reusability Increasing usability can reduce efficiency Setting objectives for quality is a key engineering activity You then design to meet the objectives Avoids over-engineering which wastes money Optimizing i i is also sometimes necessary E.g. obtain the highest possible reliability using a fixed budget 18