Selection of an appropriate project approach
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This document discusses different approaches for software project management. It describes the waterfall model, prototyping, incremental delivery, and agile methods like Dynamic System Development Method (DSDM) and Extreme Programming (XP). The key factors in selecting an approach are the level of uncertainty in requirements and technologies, the type of application being developed, and project constraints. Evolutionary or incremental approaches are best suited to higher uncertainty, while waterfall can be used for well-defined projects with tight schedules. Agile methods emphasize frequent delivery, collaboration, and responding to changing requirements.
Selection of an appropriate project approach
- 1. 1 ©The McGraw-Hill Companies, 2 Software Project Management 4th Edition Selection of an appropriate project approach Chapter 4
- 2. 2 ©The McGraw-Hill Companies, 2 Selection of project approaches • In-house development: most of these issues resolved by IS planning and standards • Software houses: more applicable as different customers have different needs • Selection of approach governed by: – uncertainties of the project – properties of application to be built
- 3. 3 ©The McGraw-Hill Companies, 2 General approach • Look at risks and uncertainties e.g. – are requirement well understood? – are technologies to be used well understood? • Look at the type of application being built e.g. – information system? embedded system? – criticality? differences between target and development environments? • Clients’ own requirements – need to use a particular method
- 4. 4 ©The McGraw-Hill Companies, 2 Choice of process models • ‘waterfall’ also known as ‘one-shot’, ‘once- through’ • incremental delivery • evolutionary development Also use of ‘agile methods’ e.g. extreme programming
- 5. 5 ©The McGraw-Hill Companies, 2 Waterfall The waterfall model
- 6. 6 ©The McGraw-Hill Companies, 2 Waterfall • the ‘classical’ model • imposes structure on the project • every stage needs to be checked and signed off • BUT – limited scope for iteration
- 7. 7 ©The McGraw-Hill Companies, 2 V-process model Another way of looking at the waterfall model
- 8. 8 ©The McGraw-Hill Companies, 2 Evolutionary delivery: prototyping ‘ An iterative process of creating quickly and inexpensively live and working models to test out requirements and assumptions’ Sprague and McNurlin main types • ‘throw away’ prototypes • evolutionary prototypes what is being prototyped? • human-computer interface • functionality
- 9. 9 ©The McGraw-Hill Companies, 2 Reasons for prototyping • learning by doing • improved communication • improved user involvement • a feedback loop is established • reduces the need for documentation • reduces maintenance costs i.e. changes after the application goes live • prototype can be used for producing expected results
- 10. 10 ©The McGraw-Hill Companies, 2 Prototyping: some dangers • users may misunderstand the role of the prototype • lack of project control and standards possible • additional expense of building prototype • focus on user-friendly interface could be at expense of machine efficiency
- 11. 11 ©The McGraw-Hill Companies, 2 Other ways of categorizing prototyping • what is being learnt? – organizational prototype – hardware/software prototype (‘experimental’) – application prototype (‘exploratory’) • to what extent – mock-ups – simulated interaction – partial working models: vertical versus horizontal
- 12. 12 ©The McGraw-Hill Companies, 2 Incremental delivery design build install evaluate design build install evaluate design build install evaluate increment 1 increment 2 increment 3 first incremental delivery second incremental delivery third incremental delivery delivered system
- 13. 13 ©The McGraw-Hill Companies, 2 The incremental process Intentional incremental delivery
- 14. 14 ©The McGraw-Hill Companies, 2 Incremental approach:benefits • feedback from early stages used in developing latter stages • shorter development thresholds • user gets some benefits earlier • project may be put aside temporarily • reduces ‘gold-plating’: BUT there are some possible disadvantages • loss of economy of scale • ‘software breakage’
- 15. 15 ©The McGraw-Hill Companies, 2 The outline incremental plan • steps ideally 1% to 5% of the total project • non-computer steps should be included • ideal if a step takes one month or less: – not more than three months • each step should deliver some benefit to the user • some steps will be physically dependent on others
- 16. 16 ©The McGraw-Hill Companies, 2 Which step first? • some steps will be pre-requisite because of physical dependencies • others may be in any order • value to cost ratios may be used – V/C where – V is a score 1-10 representing value to customer – C is a score 0-10 representing value to developers
- 17. 17 ©The McGraw-Hill Companies, 2 V/C ratios: an example step value cost ratio profit reports 9 1 9 2nd online database 1 9 0.11 5th ad hoc enquiry 5 5 1 4th purchasing plans 9 4 2.25 3rd profit- based pay for managers 9 0 inf 1st
- 18. 18 ©The McGraw-Hill Companies, 2 ‘Agile’ methods structured development methods have some perceived advantages – produce large amounts of documentation which can be largely unread – documentation has to be kept up to date – division into specialist groups and need to follow procedures stifles communication – users can be excluded from decision process – long lead times to deliver anything etc. etc The answer? ‘Agile’ methods?
- 19. 19 ©The McGraw-Hill Companies, 2 Dynamic system development method • UK-based consortium • arguably DSDM can be seen as replacement for SSADM • DSDM is more a project management approach than a development approach • Can still use DFDs, LDSs etc!
- 20. 20 ©The McGraw-Hill Companies, 2 Nine core DSDM principles 1. Active user involvement 2. Teams empowered to make decisions 3. Frequent delivery of products 4. Fitness for business purpose 5. Iterative and incremental delivery 6. Changes are reversible 7. Requirements base-lined at a high level 8. Testing integrated with development 9. Collaborative and co-operative approach
- 21. 21 ©The McGraw-Hill Companies, 2 DSDM framework Figure 4.6 here DSDM process model
- 22. 22 ©The McGraw-Hill Companies, 2 DSDM: time-boxing • time-box fixed deadline by which something has to be delivered • typically two to six weeks • MOSCOW priorities – Must have - essential – Should have - very important, but system could operate without – Could have – Want - but probably won’t get!
- 23. 23 ©The McGraw-Hill Companies, 2 Extreme programming • increments of one to three weeks – customer can suggest improvement at any point • argued that distinction between design and building of software are artificial • code to be developed to meet current needs only • frequent re-factoring to keep code structured
- 24. 24 ©The McGraw-Hill Companies, 2 Extreme programming - contd • developers work in pairs • test cases and expected results devised before software design • after testing of increment, test cases added to a consolidated set of test cases
- 25. 25 ©The McGraw-Hill Companies, 2 Grady Booch’s concern Booch, an OO authority, is concerned that with requirements driven projects: ‘Conceptual integrity sometimes suffers because this is little motivation to deal with scalability, extensibility, portability, or reusability beyond what any vague requirement might imply’ Tendency towards a large number of discrete functions with little common infrastructure?
- 26. 26 ©The McGraw-Hill Companies, 2 Macro and micro processes A macro process containing three iterative micro processes
- 27. 27 ©The McGraw-Hill Companies, 2 ‘rules of thumb’ about approach to be used IF uncertainty is high THEN use evolutionary approach IF complexity is high but uncertainty is not THEN use incremental approach IF uncertainty and complexity both low THEN use one-shot IF schedule is tight THEN use evolutionary or incremental
- 28. 28 ©The McGraw-Hill Companies, 2 Combinations of approach yes yes no yes yes yes yes yes no evolutionary incremental evolutionaryincrementalone-shot one-shot installation construction one-shot or incremental installation - any construction approach possible evolutionary installation implies evolutionary construction
Editor's Notes
- #2: <number> This talk provides an overview of the basic steps needed to produce a project plan. The framework provided should allow students to identify where some of the particular issues discussed in other chapters are applied to the planning process. As the focus is on project planning, techniques to do with project control are not explicitly described. However, in practice, one element of project planning will be to decide what project control procedures need to be in place.
- #3: Sections 4.1 and 4.2 of the textbook discuss these issues. Different types of project need different types of approach. If you are working in one particular environment which specializes in one type of software, then the approach is likely not to change much from one project to another. Where you work for different clients in different organizations developing a variety of applications then the approach for each project may need to be tailored.
- #4: See section 4.2 of the textbook.
- #5: It could be argued that extreme programming is mainly a particular way of carrying out incremental and evolutionary development
- #6: Section 4.6 of the textbook discusses this topic. We have already touched upon the Waterfall approach in Lecture/Chapter 1 when we discussed the ISO 12207. The way that the Waterfall approach is usually interpreted, it implies that all work on one phase has to be completed and checked off before the next one can start. However, it can be argued that ISO 12207 is really a technical model showing the order technical processes need to be carried out on a software component. You might break down an application into component increments, but the technical processes relating to that increment are carried out in the ISO 12207 sequence. You can, within the ISO 12207 sequence, loop back in an iterative manner, but the technical sequence still remains.
- #8: Section 4.7 of the text book discusses this topic Essentially the testing phase of the Waterfall model is expanded. For each developmental activity going down the slope of the left hand side of the V, there is a matching testing or evaluation phase as you climb up the right hand side of the V. Each activity checks the implementation of each of the develoomental stages. For example, at the system testing stage systems analyst may be checking that the design that was specified has been correctly implemented. He or she may also be checking the design itself is adequate.
- #10: A prototype is a working model of one or more aspects of the project application. It is constructed quickly and inexpensively in order to test out assumptions. Sections 4.9, 4.10 and 4.11 discuss this topic. learning by doing - useful where requirements are only partially known improved communication - users are reluctant to read massive documents, but when system is ‘live’ you get a better feeling for it improved user involvement - user ideas and requests are quickly implemented the reduction of maintenance costs – the idea is that if you do not have a prototype then the first release of the application will effectively become a prototype as users will find things that they do not like and then ask for them to be changed. It is easier and safer to make such changes before the application becomes operational. testing - involves devising test cases and then documenting the results expected when the test cases are run. If these are done by hand, then effectively you have a manual prototype. Why not get the software prototype to generate the expected results?
- #12: When a prototype is to be produced as part of a student’s final year project, then the learning objectives that the prototypes will help be achieved need to defined at project inception. The details of what has been learnt through the development and exercising of the prototype should be documented during the project.
- #13: The application to be delivered is broken down into a number of components each of which will be actually used by the users. Each of these is then developed as a separate ‘mini-project’ or increment.
- #14: This approach has had a very vocal advocate in Tom Gilb (see the book Principles of Software Engineering Management published by Addison-Wesley (1988)). Gilb argues that the initial focus should be on high level business objectives. There may be many ways in which important objectives can be achieved and we ought to allow ourselves freedom in the way we try to achieve the objectives. Open technology plan – we need to ensure that the technologies we use are ones that facilitate the addition of components to an existing application. Plan increments – the nature and order of the increments to be delivered needs to be delivered to the users have to be planned at the outset.
- #15: Advantages of prototyping feedback from early stages used in developing latter stages shorter development thresholds - important when requirements are likely to change user gets some benefits earlier - may assist cash flow project may be put aside temporarily - more urgent jobs may emerge reduces ‘gold-plating’ i.e. features requested but not used But there are possible disadvantages loss of economy of scale - some costs will be repeated ‘software breakage’ - later increments might change earlier increments
- #20: A fuller explanation can be found in Jennifer Stapleton’s DSDM: A Framework for Business-Centred Development Addison-Wesley 2002 SSADM is Structured Systems Analysis and Design Method a very heavy-weight and bureaucratic methodology that was promoted by the UK government DFD = Data Flow Diagram LDS = Logical Data Structure, effectively an Entity-Relationship Diagram
- #21: This can be seen as a re-packaging of a lot of the ideas that have been discussed under the incremental and evolutionary approaches
- #22: The feasibility/business study stage will not only look at the business feasibility of the proposed project, but also as whether DSDM would be the best framework for it. Applications where there is a prominent user interface would be prime candidates.
- #23: Time-boxes mean that the focus moves from having a fixed set of functional requirements and then extending the planned project completion until they have all been developed. The deadline is fixed and we deliver what we have completed so far even if it is not everything that was originally planned. In order to make the delivered package coherent and as useful as possible to the users, requirements are prioritized according to the MoSCoW rules.
- #24: Associated with Kent Beck - see Extreme programming explained Developed originally on Chrysler C3 payroll (Smalltalk) project Agile methods include Jim Highsmith’s Adaptive Software Development and Alistair Cocburn’s Chrystal Lite methods
- #27: Section 4.14 discusses these ideas in a little more detail