1. Software lifecycle

2. CS351 - Software Engineering (AY2004)2 Software lifecycle “student view” Design & Specification Coding Testing (optional) Hand it in >90% <10%

3. CS351 - Software Engineering (AY2004)3 Comments The “student lifecycle model” clearly has many limitations: –It doesn’t always earn you the grades you want. –It doesn’t scale. –You have little assurance of quality – somewhat of an issue for paying customers! –It isn’t consistent. We need a better model, a better process to follow, to give us a chance of delivering quality code in a timely manner.

4. CS351 - Software Engineering (AY2004)4 Software production process models Ad–hoc approach: “Code and Fix” –intuitive “model” –undesirable even for small tasks –impossible for large tasks Many formal process models exist –Waterfall Model –Spiral Model –Prototyping/Evolutionary Model Build first version Modify until Client is satisfied Operations mode Retirement Development Maintenance

5. CS351 - Software Engineering (AY2004)5 Waterfall model – overview A process model addresses these questions: –What shall we do next? –How long shall we continue to do it? A framework for software development methodology Clearly identifies –Deliverables –Standards Waterfall model provides a sequential, linear flow between phases

6. CS351 - Software Engineering (AY2004)6 Minimal waterfall model Analysis Design Code Testing Maintenance

7. CS351 - Software Engineering (AY2004)7 Waterfall model – requirements stages Feasibility study –Cost/benefit analysis –Needs understanding of problem –Deliverable - a feasibility study document Costs alternative solutions Requirements –Analysis Functionality etc of software –Specification document “Contract” between customer and software engineers Complete, precise, modifiable Specifies –Functional requirements –Non-functional requirements –Development and maintenance procedures

8. CS351 - Software Engineering (AY2004)8 Waterfall model – final stages Design and specification –Modules Preliminary and detailed design –Deliverable - design specification document –Standards Coding and module testing –Deliverable - tested modules –Standards for coding and testing, quality control Integration and system testing –Delivers running application - alpha tested within organization

9. CS351 - Software Engineering (AY2004)9 Waterfall model – final stages Delivery and maintenance –Beta testing then product delivery –Maintenance Problems –Time between requirements and maintenance phases –Integrating changes into correct phases

10. CS351 - Software Engineering (AY2004)10 Detailed waterfall model Requirements Verify Specification Verify Planning Verify Design Verify Implementation Test Integration Test Operations Mode Retirement Changed Requirements Verify Development Maintenance

11. CS351 - Software Engineering (AY2004)11 Waterfall model – example/analysis Documentation, verification and management –“Document driven" –Quality control: reviews, walk-throughs and inspections –Management: methodology, configuration and personnel Analysis –Linear, rigid, monolithic –Disciplined –Disadvantages Commitments too early Rigidity and linearity make feedback difficult Change often achieved as a "fix": distorts maintenance phase Somewhat bureaucratic

12. CS351 - Software Engineering (AY2004)12 Waterfall model - reality Requirements analysis System design Program design Program implementation Unit testing Integration testing System testing Delivery Maintenance

13. CS351 - Software Engineering (AY2004)13 Rapid prototyping model Rapid Prototyping Verify Specification Verify Planning Verify Design Verify Implementation Test Integration Test Operations Mode Retirement Changed Requirements Verify Development Maintenance

14. CS351 - Software Engineering (AY2004)14 Evolutionary model Requirements Verify Specification Verify Planning Verify Architectural design Verify For each build: perform detailed design, implementation and integration. Test. Deliver to client Operations Mode Retirement Development Maintenance

15. CS351 - Software Engineering (AY2004)15 Evolutionary model Incremental development to –Deliver partial functionality early (non-monolothic) –Provide feedback on requirements May be associated with incremental delivery –Delivered increment is a product –User provides feedback for design of next increment Approach may be combined with waterfall model –During implementation phases Requirements document identifies subsets Allowance for later change –At all stages Finer grained application of waterfall model to each increment

16. CS351 - Software Engineering (AY2004)16 Evolutionary model – prototyping Prototyping –“Throw-away” Build system once - as basis for understanding requirements Discard and rebuild –Build-upon Iterative process –Decide objectives of prototype –Plan, build and document prototype –Evaluate prototype Eventually refine into a completed system Provides feedback on requirements and functionality Facilitates understanding of requirements and interfaces Flexible Inherently less disciplined - needs careful management

17. CS351 - Software Engineering (AY2004)17 Evolutionary model – prototyping SpecificationDesign Implementation & Integration Deliver to client SpecificationDesign Implementation & Integration Deliver to client SpecificationDesign Implementation & Integration Deliver to client Build 1 Build n Build 3 Build 2 Specification team Design team Implementation/integration team SpecificationDesign Implementation & Integration Deliver to client..................

18. CS351 - Software Engineering (AY2004)18 Spiral model Verify Risk analysis Risk analysis Risk analysis Risk analysis Risk analysis R.A. Rapid prototype Specification Implementation Design Planning Integration

19. CS351 - Software Engineering (AY2004)19 Spiral model A Meta–model really –Any of the other process models can be used with it Cyclic, not linear Attempts to identify risks Usually coupled with prototyping Each “turn” around the spiral resolves more risks and (possibly) yields a prototype

20. CS351 - Software Engineering (AY2004)20 Spiral model – prototyping

21. CS351 - Software Engineering (AY2004)21 Is it worth it? Estimates for a 200,000 line data processing product: CMMDurationEffortFaults detectedFaults deliveredTotal cost Level(months)(personduring to clientof months)developmentand installeddevelopment Level 129.8593.5134861$5,440,000 Level 218.5143.032812$1,311,000 Level 315.279.51827$728,000 Level 412.542.8975$392,000 Level 59.016.0371$146,000 CMM = Capability Maturity Model CMM is a measure of an organizations ability to follow a process and refine it to suit that organization’s activities. It is covered in more detail in CS460.

22. CS351 - Software Engineering (AY2004)22 Observations We need to understand the software development lifecycle and have a process in place to help us deliver software on-time and within budget. Error rates and cost of development decrease the more we understand the software process. While discussion on requirements gathering etc is defered until CS460, we can certainly do a great deal to improve our own software by understanding what we do when we build software systems. As individuals, we most likely follow one of the lifecycle models described earlier – or a hybrid of one or more of the models. We may skip some steps, we may not pay sufficient attention to some aspects.

23. CS351 - Software Engineering (AY2004)23 Our behavior A better understanding of our personal behavior will help us fit into a team environment better, and will help us deliver higher quality code. To understand what we do, we must objectively assess what we do. –This is difficult as we first have to overcome our belief that we are doing everything correctly. –We have to examine what we do and constantly ask “how can I improve?” –We have to measure what we do in order to know if the changes we make are working, and to identify those aspects of our behavior that require change.

24. CS351 - Software Engineering (AY2004)24 Personal software process We have already seen the personal software process as a means to identify several of the common errors we make. You should apply the PSP to all code you write – not just for this subject. Over time you will gather the information on yourself that you need to see what needs improving. –It will then, of course, be up to you to address those deficiencies and improve. –You should continue to use the PSP to measure the success of your changes and to identify further areas for improvement.

25. CS351 - Software Engineering (AY2004)25 Journal If addition to the use of the PSP, we also recommend you need a journal. A journal is where you record all of your thoughts, design your algorithms, plan the testing strategy for these algorithms, make notes on the performance of your code, make notes on the kinds of errors you make, record how you ntend to rectify these deficiencies, … You record everything related to software development. You should throw nothing away. Ideally, the journal is a bound book with numbered pages. At regular intervals (every few months), you should read through your journal and look for trends, look for errors you regularly make, look for things you don’t understand. Once identified, plan a strategy to deal with these issues – record the plan in the journal and stick to it.

26. CS351 - Software Engineering (AY2004)26 Summary This course focuses on your personal ability to produce high quality software. You should make observations in your journal of errors you make including: –Not fully understanding the requirements –Poor testing –Typical coding errors –Poorly designed interfaces –Integration issues These are all aspects of the software lifecycle If we can get things right as an individual, we have a better chance of getting things right in a team.