agility_principles.ppt
- 2. Common Fears for Developers • The project will produce the wrong product. • The project will produce a product of inferior quality. • The project will be late. • We’ll have to work 80 hour weeks. • We’ll have to break commitments. • We won’t be having fun.
- 3. What is “Agility”? • Effective (rapid and adaptive) response to change • Effective communication among all stakeholders • Drawing the customer onto the team • Organizing a team so that it is in control of the work performed Yielding … • Rapid, incremental delivery of software
- 4. An Agile Process • Is driven by customer descriptions of what is required (scenarios) • Recognizes that plans are short-lived • Develops software iteratively with a heavy emphasis on construction activities • Delivers multiple ‘software increments’ • Adapts as changes occur
- 5. Principles of agile methods Principle Description Customer involvement The customer should be closely involved throughout the development process. Their role is provide and prioritise new system requirements and to evaluate the iterations of the system. Incremental delivery The software is developed in increments with the customer specifying the requirements to be included in each increment. People not process The skills of the development team should be recognised and exploited. The team should be left to develop their own ways of working without prescriptive processes. Embrace change Expect the system requirements to change and design the system so that it can accommodate these changes. Maintain simplicity Focus on simplicity in both the software being developed and in the development process used. Wherever possible, actively work to eliminate complexity from the system.
- 6. Agile process models • Extreme Programming (XP) • Scrum • Adaptive Software Development • Dynamic System Development Method (DSDM) • Crystal • Feature Driven Development • Agile Modeling (AM)
- 7. Extreme Programming (XP) • Perhaps the best-known and most widely used agile method. • Extreme Programming (XP) takes an ‘extreme’ approach to iterative development. – New versions may be built several times per day; – Increments are delivered to customers every 2 weeks; – All tests must be run for every build and the build is only accepted if tests run successfully. • XP Values – Communication – Simplicity – Feedback – Courage – Respect
- 9. Extreme Programming (XP) • XP Planning – Begins with the creation of user stories – Agile team assesses each story and assigns a cost – Stories are grouped to for a deliverable increment – A commitment is made on delivery date – After the first increment project velocity is used to help define subsequent delivery dates for other increments
- 10. Extreme Programming (XP) • XP Design – Follows the KIS (keep it simple) principle – Encourage the use of CRC (class-responsibility- cards) cards – For difficult design problems, suggests the creation of spike solutions — a design prototype – Encourages refactoring — an iterative refinement of the internal program design • XP Coding – Recommends the construction of a unit test for a store before coding commences – Encourages pair programming
- 11. Extreme Programming (XP) • XP Testing – All unit tests are executed daily – Acceptance tests are defined by the customer and executed to assess customer visible functionality
- 12. XP and agile principles • Incremental development is supported through small, frequent system releases. • Customer involvement means full-time customer engagement with the team. • People not process through pair programming, collective ownership and a process that avoids long working hours. • Change supported through regular system releases. • Maintaining simplicity through constant refactoring of code.
- 13. Customer involvement • Customer involvement is a key part of XP where the customer is part of the development team. • The role of the customer is: – To help develop stories that define the requirements – To help prioritize the features to be implemented in each release – To help develop acceptance tests which assess whether or not the system meets its requirements.
- 14. Requirements scenarios • In XP, user requirements are expressed as scenarios or user stories. • These are written on cards and the development team break them down into implementation tasks. These tasks are the basis of schedule and cost estimates. • The customer chooses the stories for inclusion in the next release based on their priorities and the schedule estimates.
- 15. Story card for document downloading Downloading and printing an article First, you select the article that you want f rom a displayed list. You then have to tell the system how you will pay for it - this can either be through a subscription, through a company account or by credit card. After this, you get a copyright f orm from the system to fill in and, when you have submitted this, the article you want is downloaded onto your computer. You then choose a printer and a copy ofthe article is printed. You tell the system ifprinting has been successful. Ifthe article is a print-only article, you canÕt keep the PDF version so it is automatically deleted from your computer.
- 16. XP and change • Conventional wisdom in software engineering is to design for change. It is worth spending time and effort anticipating changes as this reduces costs later in the life cycle. • XP, however, maintains that this is not worthwhile as changes cannot be reliably anticipated. • Rather, it proposes constant code improvement (refactoring) to make changes easier when they have to be implemented.
- 17. Refactoring • Refactoring is the process of code improvement where code is reorganised and rewritten to make it more efficient, easier to understand, etc. • Refactoring is required because frequent releases mean that code is developed incrementally and therefore tends to become messy. • Refactoring should not change the functionality of the system. • Automated testing simplifies refactoring as you can see if the changed code still runs the tests successfully.
- 18. Testing in XP • Test-first development. • Incremental test development from scenarios. • User involvement in test development and validation. • Automated test harnesses are used to run all component tests each time that a new release is built.
- 19. Task cards for document downloading Task 1: Implement principal workflow Task 2: Implement article catalog and selection Task 3: Implement payment collection Payment may be made in 3 different ways. The user selects which way they wish to pay. Ifthe user has a library subscription, then they can input the subscriber key which should be checked by the system. Alternatively, they can input an organisational account number. Ifthis is valid, a debit of the cost of the article is posted to this account. Finally, they may input a 16 digit credit card number and expiry date. This should be checked for validity and, if valid a debit is posted to that credit card account.
- 20. Test case description Test 4: Test credit card validity Input: Astring re pr e sentingthecred itcardnumbera nd twointege rsr eprese nting the month and year when the card expires Tests: Check that all bytes in the string are digits Check that the month lies between 1 and 12 and the year is greater than or equal to the current year . Using the first 4 digits ofthe credit card number , check that the card issuer is valid by looking up the card issuer table. Check credit card validity by submitting the card number and expiry date information to the card issuer Output: OK or error message indicating that the card is invalid
- 21. Test-first development • Writing tests before code clarifies the requirements to be implemented. • Tests are written as programs rather than data so that they can be executed automatically. The test includes a check that it has executed correctly. • All previous and new tests are automatically run when new functionality is added. Thus checking that the new functionality has not introduced errors.
- 22. Pair programming • In XP, programmers work in pairs, sitting together to develop code. • This helps develop common ownership of code and spreads knowledge across the team. • It serves as an informal review process as each line of code is looked at by more than 1 person. • It encourages refactoring as the whole team can benefit from this. • Measurements suggest that development productivity with pair programming is similar to that of two people working independently.
- 23. Problems with XP • Customer involvement – This is perhaps the most difficult problem. It may be difficult or impossible to find a customer who can represent all stakeholders and who can be taken off their normal work to become part of the XP team. For generic products, there is no ‘customer’ - the marketing team may not be typical of real customers. • Architectural design – The incremental style of development can mean that inappropriate architectural decisions are made at an early stage of the process. – Problems with these may not become clear until many features have been implemented and refactoring the architecture is very expensive.
- 24. • Test complacency – It is easy for a team to believe that because it has many tests, the system is properly tested. – Because of the automated testing approach, there is a tendency to develop tests that are easy to automate rather than tests that are ‘good’ tests.
- 25. Key points • Extreme programming includes practices such as systematic testing, continuous improvement and customer involvement. • Customers are involved in developing requirements which are expressed as simple scenarios. • The approach to testing in XP is a particular strength where executable tests are developed before the code is written. • Key problems with XP include difficulties of getting representative customers and problems of architectural design.