Lecture 03. Software Process Models PDF

SOFTWARE ENGINEERING Software Process Models  Topics covered Classical Models Agile Method 30/10/2014 Chapter 2 Software Processes 2  Software process models 30/10/2014 Chapter 2 Software Processes 3 Classical Models  Waterfall Mo...

SOFTWARE ENGINEERING Software Process Models  Topics covered Classical Models Agile Method 30/10/2014 Chapter 2 Software Processes 2  Software process models 30/10/2014 Chapter 2 Software Processes 3 Classical Models  Waterfall Model The waterfall model is a sequential, plan driven-process where you must plan and schedule all your activities before starting the project. Each activity in the waterfall model is represented as a separate phase arranged in linear order. It has the following phases: Requirements Design Implementation Testing Deployment Maintenance  The waterfall model 30/10/2014 Chapter 2 Software Processes 6  V Model The V model (Verification and Validation model) is an extension of the waterfall model. All the requirements are gathered at the start and cannot be changed. You have a corresponding testing activity for each stage. For every phase in the development cycle, there is an associated testing phase. V-model  Incremental Model The incremental model divides the system’s functionality into small increments that are delivered one after the other in quick succession. The most important functionality is implemented in the initial increments. The subsequent increments expand on the previous ones until everything has been updated and implemented. Incremental development is based on developing an initial implementation, exposing it to user feedback, and evolving it through new versions. The process’ activities are interwoven by feedback. 30/10/2014 Chapter 2 Software Processes 9 Incremental Model  Iterative Model The iterative development model develops a system through building small portions of all the features. This helps to meet initial scope quickly and release it for feedback. In the iterative model, you start off by implementing a small set of the software requirements. These are then enhanced iteratively in the evolving versions until the system is completed. This process model starts with part of the software, which is then implemented and reviewed to identify further requirements. Iterative Model  RAD Model The Rapid Application Development (RAD model) is based on iterative development and prototyping with little planning involved. You develop functional modules in parallel for faster product delivery. It involves the following phases: Business modeling Data modeling Process modeling Application generation Testing and turnover RAD Model  Spiral Model The spiral model is a risk driven iterative software process model. The spiral model delivers projects in loops. Unlike other process models, its steps aren’t activities but phases for addressing whatever problem has the greatest risk of causing a failure. It was designed to include the best features from the waterfall and introduces risk-assessment. You have the following phases for each cycle: 1. Address the highest-risk problem and determine the objective and alternate solutions 2. Evaluate the alternatives and identify the risks involved and possible solutions 3. Develop a solution and verify if it’s acceptable 4. Plan for the next cycle Spiral Model  Agile methods 30/10/2014 Chapter 3 Agile Software Development 17  Agile methods Dissatisfaction with the overheads involved in software design methods of the 1980s and 1990s led to the creation of agile methods. These methods: Focus on the code rather than the design Are based on an iterative approach to software development Are intended to deliver working software quickly and evolve this quickly to meet changing requirements. The aim of agile methods is to reduce overheads in the software process (e.g. by limiting documentation) and to be able to respond quickly to changing requirements without excessive rework. 30/10/2014 Chapter 3 Agile Software Development 18  Agile manifesto We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value: Individuals and interactions over processes and tools Working software over comprehensive documentation Customer collaboration over contract negotiation Responding to change over following a plan That is, while there is value in the items on the right, we value the items on the left more. 30/10/2014 Chapter 3 Agile Software Development 19  The principles of agile methods Principle Description Customer involvement Customers should be closely involved throughout the development process. Their role is provide and prioritize 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 recognized and exploited. Team members should be left to develop their own ways of working without prescriptive processes. Embrace change Expect the system requirements to change and so design the system to accommodate these changes. Maintain simplicity Focus on simplicity in both the software being developed and in the development process. Wherever possible, actively work to eliminate complexity from the system. 30/10/2014 Chapter 3 Agile Software Development 20  Agile method applicability Product development where a software company is developing a small or medium-sized product for sale. Virtually all software products and apps are now developed using an agile approach Custom system development within an organization, where there is a clear commitment from the customer to become involved in the development process and where there are few external rules and regulations that affect the software. 30/10/2014 Chapter 3 Agile Software Development 21 Agile development techniques 30/10/2014 Chapter 3 Agile Software Development 22  Extreme programming A very influential agile method, developed in the late 1990s, that introduced a range of agile development techniques. 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. 30/10/2014 Chapter 3 Agile Software Development 23 The extreme programming release cycle 30/10/2014 Chapter 3 Agile Software Development 24  Extreme programming practices (a) Principle or practice Description Incremental planning Requirements are recorded on story cards and the stories to be included in a release are determined by the time available and their relative priority. The developers break these stories into development ‘Tasks’. See Figures 3.5 and 3.6. Small releases The minimal useful set of functionality that provides business value is developed first. Releases of the system are frequent and incrementally add functionality to the first release. Simple design Enough design is carried out to meet the current requirements and no more. Test-first development An automated unit test framework is used to write tests for a new piece of functionality before that functionality itself is implemented. Refactoring All developers are expected to refactor the code continuously as soon as possible code improvements are found. This keeps the code simple and maintainable. 30/10/2014 Chapter 3 Agile Software Development 25  Extreme programming practices (b) Pair programming Developers work in pairs, checking each other’s work and providing the support to always do a good job. Collective ownership The pairs of developers work on all areas of the system, so that no islands of expertise develop and all the developers take responsibility for all of the code. Anyone can change anything. Continuous integration As soon as the work on a task is complete, it is integrated into the whole system. After any such integration, all the unit tests in the system must pass. Sustainable pace Large amounts of overtime are not considered acceptable as the net effect is often to reduce code quality and medium term productivity On-site customer A representative of the end-user of the system (the customer) should be available full time for the use of the XP team. In an extreme programming process, the customer is a member of the development team and is responsible for bringing system requirements to the team for implementation. 30/10/2014 Chapter 3 Agile Software Development 26  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. 30/10/2014 Chapter 3 Agile Software Development 27  Influential XP practices Extreme programming has a technical focus and is not easy to integrate with management practice in most organizations. Consequently, while agile development uses practices from XP, the method as originally defined is not widely used. Key practices User stories for specification Refactoring Test-first development Pair programming 30/10/2014 Chapter 3 Agile Software Development 28  User stories for requirements In XP, a customer or user is part of the XP team and is responsible for making decisions on requirements. User requirements are expressed as user stories or scenarios. 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. 30/10/2014 Chapter 3 Agile Software Development 29  Refactoring 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. 30/10/2014 Chapter 3 Agile Software Development 30  Refactoring Programming team look for possible software improvements and make these improvements even where there is no immediate need for them. This improves the understandability of the software and so reduces the need for documentation. Changes are easier to make because the code is well-structured and clear. However, some changes requires architecture refactoring and this is much more expensive. 30/10/2014 Chapter 3 Agile Software Development 31  Examples of refactoring Re-organization of a class hierarchy to remove duplicate code. Tidying up and renaming attributes and methods to make them easier to understand. The replacement of inline code with calls to methods that have been included in a program library. 30/10/2014 Chapter 3 Agile Software Development 32  Test-first development Testing is central to XP and XP has developed an approach where the program is tested after every change has been made. XP testing features: 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. 30/10/2014 Chapter 3 Agile Software Development 33  Test-driven 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. Usually relies on a testing framework such as Junit. All previous and new tests are run automatically when new functionality is added, thus checking that the new functionality has not introduced errors. 30/10/2014 Chapter 3 Agile Software Development 34  Customer involvement The role of the customer in the testing process is to help develop acceptance tests for the stories that are to be implemented in the next release of the system. The customer who is part of the team writes tests as development proceeds. All new code is therefore validated to ensure that it is what the customer needs. However, people adopting the customer role have limited time available and so cannot work full-time with the development team. They may feel that providing the requirements was enough of a contribution and so may be reluctant to get involved in the testing process. 30/10/2014 Chapter 3 Agile Software Development 35  Test automation Test automation means that tests are written as executable components before the task is implemented These testing components should be stand-alone, should simulate the submission of input to be tested and should check that the result meets the output specification. An automated test framework (e.g. Junit) is a system that makes it easy to write executable tests and submit a set of tests for execution. As testing is automated, there is always a set of tests that can be quickly and easily executed Whenever any functionality is added to the system, the tests can be run and problems that the new code has introduced can be caught immediately. 30/10/2014 Chapter 3 Agile Software Development 36  Problems with test-first development Programmers prefer programming to testing and sometimes they take short cuts when writing tests. For example, they may write incomplete tests that do not check for all possible exceptions that may occur. Some tests can be very difficult to write incrementally. For example, in a complex user interface, it is often difficult to write unit tests for the code that implements the ‘display logic’ and workflow between screens. It difficult to judge the completeness of a set of tests. Although you may have a lot of system tests, your test set may not provide complete coverage. 30/10/2014 Chapter 3 Agile Software Development 37  Pair programming Pair programming involves programmers working in pairs, developing code together. 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 improving the system code. 30/10/2014 Chapter 3 Agile Software Development 38  Pair programming In pair programming, programmers sit together at the same computer to develop the software. Pairs are created dynamically so that all team members work with each other during the development process. The sharing of knowledge that happens during pair programming is very important as it reduces the overall risks to a project when team members leave. Pair programming is not necessarily inefficient and there is some evidence that suggests that a pair working together is more efficient than 2 programmers working separately. 30/10/2014 Chapter 3 Agile Software Development 39 Agile project management with Scrum 30/10/2014 Chapter 3 Agile Software Development 40  Agile project management The principal responsibility of software project managers is to manage the project so that the software is delivered on time and within the planned budget for the project. The standard approach to project management is plan-driven. Managers draw up a plan for the project showing what should be delivered, when it should be delivered and who will work on the development of the project deliverables. Agile project management requires a different approach, which is adapted to incremental development and the practices used in agile methods. 30/10/2014 Chapter 3 Agile Software Development 41  Scrum Scrum is an agile method that focuses on managing iterative development rather than specific agile practices. There are three phases in Scrum. The initial phase is an outline planning phase where you establish the general objectives for the project and design the software architecture. This is followed by a series of sprint cycles, where each cycle develops an increment of the system. The project closure phase wraps up the project, completes required documentation such as system help frames and user manuals and assesses the lessons learned from the project. 30/10/2014 Chapter 3 Agile Software Development 42  Scrum terminology (a) Scrum term Definition A self-organizing group of software developers, which should be no Development team more than 7 people. They are responsible for developing the software and other essential project documents. The software increment that is delivered from a sprint. The idea is that this should be ‘potentially shippable’ which means that it is in a Potentially shippable finished state and no further work, such as testing, is needed to product increment incorporate it into the final product. In practice, this is not always achievable. This is a list of ‘to do’ items which the Scrum team must tackle. They may be feature definitions for the software, software requirements, user stories or descriptions of supplementary tasks Product backlog that are needed, such as architecture definition or user documentation. An individual (or possibly a small group) whose job is to identify product features or requirements, prioritize these for development and continuously review the product backlog to ensure that the Product owner project continues to meet critical business needs. The Product Owner can be a customer but might also be a product manager in a software company or other stakeholder representative. Chapter 3 Agile Software Development 43  Scrum terminology (b) Scrum term Definition A daily meeting of the Scrum team that reviews progress and prioritizes Scrum work to be done that day. Ideally, this should be a short face-to-face meeting that includes the whole team. The ScrumMaster is responsible for ensuring that the Scrum process is followed and guides the team in the effective use of Scrum. He or she is responsible for interfacing with the rest of the company and for ensuring that the Scrum team is not diverted by outside interference. The Scrum ScrumMaster developers are adamant that the ScrumMaster should not be thought of as a project manager. Others, however, may not always find it easy to see the difference. A development iteration. Sprints are usually 2-4 weeks long. Sprint An estimate of how much product backlog effort that a team can cover in a single sprint. Understanding a team’s velocity helps them estimate Velocity what can be covered in a sprint and provides a basis for measuring improving performance. 30/10/2014 Chapter 3 Agile Software Development 44  Scrum sprint cycle 30/10/2014 Chapter 3 Agile Software Development 45  The Scrum sprint cycle Sprints are fixed length, normally 2–4 weeks. The starting point for planning is the product backlog, which is the list of work to be done on the project. The selection phase involves all of the project team who work with the customer to select the features and functionality from the product backlog to be developed during the sprint. 30/10/2014 Chapter 3 Agile Software Development 46  The Sprint cycle Once these are agreed, the team organize themselves to develop the software. During this stage the team is isolated from the customer and the organization, with all communications channelled through the so-called ‘Scrum master’. The role of the Scrum master is to protect the development team from external distractions. At the end of the sprint, the work done is reviewed and presented to stakeholders. The next sprint cycle then begins. 30/10/2014 Chapter 3 Agile Software Development 47  Teamwork in Scrum The ‘Scrum master’ is a facilitator who arranges daily meetings, tracks the backlog of work to be done, records decisions, measures progress against the backlog and communicates with customers and management outside of the team. The whole team attends short daily meetings (Scrums) where all team members share information, describe their progress since the last meeting, problems that have arisen and what is planned for the following day. This means that everyone on the team knows what is going on and, if problems arise, can re-plan short-term work to cope with them. 30/10/2014 Chapter 3 Agile Software Development 48  Scrum benefits The product is broken down into a set of manageable and understandable chunks. Unstable requirements do not hold up progress. The whole team have visibility of everything and consequently team communication is improved. Customers see on-time delivery of increments and gain feedback on how the product works. Trust between customers and developers is established and a positive culture is created in which everyone expects the project to succeed. 30/10/2014 Chapter 3 Agile Software Development 49  Distributed Scrum 30/10/2014 Chapter 3 Agile Software Development 50