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- 2. 2 Course outline • Unit 1: Software Engineering Basics Unit 2: Process Models and Software Life Cycles • Unit 3: Software Requirements • Unit 4: Unified Modeling Language (UML) • Unit 5: Design Basics and Software Architecture • Unit 6: OO Analysis and Design • Unit 7: Design Patterns • Unit 8: Testing and Reliability • Unit 9: Software Engineering Management and Economics
- 3. 3 Reference • These slides are based on: – Lecture slides by Ian Summerville, see http://www.comp.lancs.ac.uk/computing/resources/ser/
- 4. 4 Overview • Build-and-fix model • Waterfall model • Rapid prototyping model • Incremental model • Evolutionary • Synchronize-and-stabilize model • Spiral model
- 5. 5 Software Life-Cycle Models • Life-cycle model (also, process model) • The software development and operation activities and their ordering – Requirements elicitation – Specification – Design – Implementation – Integration – Maintenance phase – Retirement – …
- 6. 6 New or changed requirements New or changed system Software Engineering Process What Is a Software Engineering Process? A process defines Who is doing What, When and How in the development of a software system – Roles and workflows – Workproducts – Milestones – Guideline – …
- 8. 8 An Effective Process ... • Provides guidelines for efficient development of quality software • Reduces risk and increases predictability • Captures and presents best practices – Learn from other’s experiences – Mentor on your desktop – Extension of training material • Promotes common vision and culture • Provides roadmap for applying tools • Delivers information on-line, at your finger tips
- 9. 9 Lightweight vs. Heavyweight Processes Document driven Elaborate workflow definitions Many different roles Many checkpoints High management overhead Highly bureaucratic Focus on working code rather than documentation Focus on direct communication (between developers and between developers and the customer) Low management overhead Heavyweight e.g., V-Process Customizable Framework e.g., Rational Unified Process (RUP) Agile (Lightweight) e.g., eXtreme Programming (XP)
- 10. 10 • Process used should depend on type of product which is being developed – For large systems, management is usually the principal problem so you need a strictly managed process. For smaller systems, more informality is possible. • High costs may be incurred if you force an inappropriate process on a development team Process choice ©Ian Sommerville 1995 [modified]
- 11. 11 Build and Fix Model • Properties – No planning or analysis – The working program is the only workproduct • Advantage – Appropriate for small programs written by one person • Disadvantage – Understandability and maintainability decrease rapidly with increasing program size – Totally unsatisfactory – Need a life-cycle model • “Game plan” • Phases • Milestones
- 12. 12 Waterfall Model • Characterized by – Sequential steps (phases) – Feedback loops (between two phases in development) – Documentation-driven • Advantages – Documentation – Maintenance easier • Disadvantages – Complete and frozen specification document up-front often not feasible in practice – Customer involvement in the first phase only – Sequential and complete execution of phases often not desirable – Process difficult to control – The product becomes available very late in the process
- 13. 13 Rapid Prototyping Model • Rapid prototyping phase followed by waterfall – Do not turn the rapid prototype into the product – Rapid prototyping may replace the specification phase—never the design phase • Comparison: – Waterfall model—try to get it right the first time – Rapid prototyping—frequent change, then discard
- 14. 14 Advantages and Disadvantages • Advantages – Requirements better specified and validated – Early feasibility analysis – Strong involvement of the customer in the prototyping phase • Disadvantage – Higher development effort – Danger that due to schedule slip, the prototype becomes part of the product
- 15. 15 Incremental Design Coding Test Deployment Design Coding Test Deployment Design Coding Test Deployment Requirements Release 1 Release 2 Release 3 Each release adds more functionality, i.e., a new increment (Some call it iterative)
- 16. 16 Incremental Model (contd) • Waterfall, rapid prototyping models – Operational quality complete product at end • Incremental model – Operational quality portion of product within weeks • Less traumatic • Smaller capital outlay, rapid return on investment
- 17. 17 Evolutionary Design Coding Test DeploymentRequirements Design Coding Test DeploymentRequirements Design Coding Test DeploymentRequirements Feedback Version 1 Version 1 Version 1 New versions implement new and evolving requirements (Some call it iterative)
- 18. 18 Evolutionary Model (contd) • Advantages – Constant customer involvement and validation – Allows for good risk management • Disadvantages – Build-and-fix danger – Contradiction in terms
- 19. 19 Spiral model • Waterfall model plus risk analysis preceding each phase and evaluation following each phase • Prototyping for high-risk specifications • Radial dimension: cumulative cost to date • Angular dimension: progress through the spiral • If all risks cannot be resolved, the project is immediately terminated • Appropriate only for big projects (high management overhead)
- 20. 20 Spiral model Risk analysis Risk analysis Risk analysis Risk analysisProto- type 1 Prototype 2 Prototype 3 Opera- tional protoype Conceptof Operation Simulations, models, benchmarks S/W requirements Requirement validation Design V&V Product design Detailed design Code Unittest Integration testAcceptance testService Develop, verify next-levelproduct Evaluate alternatives identify, resolve risks Determine objectives alternativesand constraints Plannextphase Integration andtestplan Development plan Requirementsplan Life-cycle plan REVIEW
- 21. 21 Process model risk problems • Waterfall – High risk for new systems because of specification and design problems – Low risk for well-understood developments using familiar technology • Prototyping – Low risk for new applications because specification and program stay in step – High risk because of lack of process visibility • Evolutionary and Spiral – Middle ground between waterfall and prototyping
- 22. 22 Hybrid process models • Large systems are usually made up of several sub-systems • The same process model need not be used for all subsystems • Prototyping for high-risk specifications • Waterfall model for well-understood developments • Taylor the process to a problem
- 23. 23 Use of the Models in Practice
- 24. 24 • The fundamental problem with software – The software process is badly managed • Understanding existing processes • Introducing process changes to achieve organisational objectives which are usually focused on quality improvement, cost reduction and schedule acceleration Process improvement ©Ian Sommerville 1995 [modified]
- 25. 25 Reference • These slides are based on: – Lecture slides by Ian Summerville, see http://www.comp.lancs.ac.uk/computing/resources/ser/
- 26. 26 Rational Unified Process – Main Characteristics • Iterative and incremental • Use-case-driven • Architecture-centric • Uses UML as its modeling notation • Process framework – Comprehensive set of document templates, process workflow templates, and process guidelines – Distributed by IBM/Rational on a CD
- 27. 27 Rational Unified Process Is Use- Case-Driven • Use cases are concise, simple, and understandable by a wide range of stakeholders – End users, developers and acquirers understand functional requirements of the system • Use cases drive numerous activities in the process: – Creation and validation of the design model – Definition of test cases and procedures of the test model – Planning of iterations – Creation of user documentation – System deployment • Use cases help synchronize the content of different models
- 28. 28 Rational Unified Process Is Architecture-Centric • Architecture is the focus of the elaboration phase – Building, validating, and baselining the architecture constitute the primary objective of elaboration • The Architectural Prototype validates the architecture and serves as the baseline for the rest of development • The Software Architecture Description is the primary artifact that documents the architecture chosen • Other artifacts derive from architecture: – Design guidelines including use of patterns and idioms – Product structure – Team structure
- 29. 29 Representing Architecture: The 4+1 View Model Process View Deployment View Logical View Implementation View Programmers Software management Performance Scalability Throughput System Integrators System topology Delivery, installation communication System Engineering Use-Case View Structure Analysts/ Designers End-user Functionality
- 30. 30 InceptionInception ElaborationElaboration ConstructionConstruction TransitionTransition Process Architecture - Lifecycle Phases The Rational Unified Process has four phases: – Inception - Define the scope of project – Elaboration - Plan project, specify features, baseline architecture – Construction - Build the product – Transition - Transition the product into end user community time
- 31. 31 InceptionInception ElaborationElaboration ConstructionConstruction TransitionTransition Phase Boundaries Mark Major Milestones Lifecycle Objective Milestone Lifecycle Architecture Milestone Initial Operational Capability Milestone Product Release time
- 32. 32 Iterations and Phases AnAn iterationiteration is a distinct sequence of activities with anis a distinct sequence of activities with an established plan and evaluation criteria, resulting inestablished plan and evaluation criteria, resulting in an executable release (internal or external)an executable release (internal or external) PreliminaryPreliminary IterationIteration Architect.Architect. IterationIteration Architect.Architect. IterationIteration Devel.Devel. IterationIteration Devel.Devel. IterationIteration Devel.Devel. IterationIteration TransitionTransition IterationIteration TransitionTransition IterationIteration InceptionInception ElaborationElaboration ConstructionConstruction TransitionTransition Minor Milestones: Releases
- 33. 33 Major Workflows Produce Models Analysis &Analysis & DesignDesign Design Model Implementation Model Test Model realized by implemented by verified by RequirementsRequirements ImplementationImplementation TestTest Use-Case Model BusinessBusiness ModelingModeling Business Model supported by
- 34. 34 RUP Overview Management Environment Business Modeling Implementation Test Architecture & Design Preliminary Iteration(s) Iter. #1 Phases Process Workflows Iterations Supporting Workflows Iter. #2 Iter. #n Iter. #n+1 Iter. #n+2 Iter. #m Iter. #m+1 Deployment Configuration Mgmt Requirements Elaboration TransitionInception Construction Workflows group activities logically In an iteration, you walk through all workflows
- 35. 35 XP Overview Characteristics • Evolutionary development • Collection of 12 „Best Practices“ • Focus on working code that implements customer needs (rather than documents) • Testing is a crucial element of the process • Focus on flexibility and efficiency of the process • Designed for small teams (<10) Write tests Planning Test Pair Programming + Refactoring Integration Min. daily Every 2-3 weeks Release
- 36. 36 XP Practices (I) • The planning game – Stakeholder meeting to plan the next iteration – Business people decide on business value of features – Developers on the technical risk of features and predicted effort per feature • Small releases – Start with the smallest useful feature set; release early and often, adding a few features each time • Metaphor – Each project has an organizing metaphor, a providing easy to remember naming conventions
- 37. 37 XP Practices (II) • Simple Design – Always use the simplest possible design that gets the job done (runs the tests and states intentions of the programmer) – No speculative genericity • Testing – Test-first: write test, then implement it – Programmers write unit tests and customers write acceptance tests • Refactoring – Refactoring is done continuously; the code is always kept clean
- 38. 38 XP Practices (III) • Pair programming – All production code written by two programmers – One programmer is thinking about implementing the current method, the other is thinking strategically about the whole system – Pairs are put together dynamically • Collective code ownership – Any programmer that sees an opportunity to add value to any portion of the code is required to do so at any time • Continuous integration – Use of version and configuration management (e.g., CVS) – All changes are integrated into the code-base at least daily – The tests have to run 100% before and after the integration
- 39. 39 XP Practices (IV) • 40-h week – Programmers go home on time – Overtime is a symptom of a serious problem – No errors by tired developers; better motivated developers • On-site customer – Development team has continuous access to a real life customer/user • Coding standards – Everyone codes to the same standards – Ideally, you should not be able to tell by looking at it who has written a specific piece of code
- 40. 40 XP Advantages • Integrated, simple concept • Low management overhead (no complicated procedures to follow, no documentation to maintain, direct communication, pair programming) • Continuous risk management (early feedback from the customer) • Continuous effort estimation • Emphasis on testing; tests help in evolution and maintenance
- 41. 41 XP Disadvantages • Appropriate for small teams (up to 10 developers) only (does not scale) • Large development groups may require more structures and documents • If maintainers are not the people that developed the code, good documentation is necessary • Generic design may be necessary to enable expected future development
- 42. 42 Reading • RUP – Craig Larman, Applying UML and Patterns: An Introduction to Object- Oriented Analysis and Design and the Unified Process, Prentice-Hall, 2002 (2nd edition) – Kendall Scott. The Unified Process Explained. Addison Wesley, 2001 • Agile development – Kent Beck, Extreme Programming: Explained, Addison-Wesley, 1999 – R. Jeffries, C. Hendrikson, A. Anderson, Extreme Programming Installed, Addison-Wesley, 2001 • http://member.netease.com/~wooce/tip/se/ – Alistair Cockburn, Agile Software Development, Addison-Wesley 2002 • Online-Ressourcen – http://www.xprogramming.com – http://www.xprogramming.org – http://groups.yahoo.com/group/extremeprogramming – http://c2.com
- 43. 43 Process improvement stages • Process analysis – Model and analyse (quantitatively if possible) existing processes • Improvement identification – Identify quality, cost or schedule bottlenecks • Process change introduction – Modify the process to remove identified bottlenecks • Process change training – Train staff involved in new process proposals • Change tuning – Evolve and improve process improvements ©Ian Sommerville 1995
- 44. 44 Software process improvement initiatives • Capability maturity model (CMM) – http://www.sei.cmu.edu/cmm/cmms/cmms.html • ISO 9000-series • ISO/IEC 15504 – Standard for Software Process Assessment (SPICE) – http://www-sqi.cit.gu.edu.au/spice/ ©Steven Schach 2002 [modified]
- 45. 45 Capability Maturity Model • A set of strategies for improving the software process – SW–CMM for software – P–CMM for human resources (“people”) – SE–CMM for systems engineering – IPD–CMM for integrated product development – SA–CMM for software acquisition • These strategies are being unified into CMMI (capability maturity model integration) • Developed by Software Engineering Institute (SEI) ©Steven Schach 2002 [modified]
- 46. 46 SW–CMM • A strategy for improving the software process • Put forward in 1986 by the SEI • Fundamental ideas: – Improving the software process leads to • Improved software quality • Delivery on time, within budget – Improved management leads to • Improved techniques • Five levels of “maturity” are defined • Organization advances stepwise from level to level ©Steven Schach 2002
- 47. 47 Level 1. Initial Level • Ad hoc approach – Entire process is unpredictable – Management consists of responses to crises • Most organizations world-wide are at level 1 ©Steven Schach 2002
- 48. 48 Level 2. Repeatable Level • Basic software management – Management decisions should be made on the basis of previous experience with similar products – Measurements (“metrics”) are made – These can be used for making cost and duration predictions in the next project – Problems are identified, immediate corrective action is taken ©Steven Schach 2002
- 49. 49 Level 3. Defined Level • The software process is fully documented – Managerial and technical aspects are clearly defined – Continual efforts are made to improve quality, productivity – Reviews are performed to improve software quality – CASE tools are applicable now (and not at levels 1 or 2) ©Steven Schach 2002
- 50. 50 Level 4. Managed Level • Quality and productivity goals are set for each project – Quality, productivity are continually monitored – Statistical quality controls are in place ©Steven Schach 2002
- 51. 51 Level 5. Optimizing Level • Continuous process improvement – Statistical quality and process controls – Feedback of knowledge from each project to the next ©Steven Schach 2002
- 52. 52 SW–CMM Summary ©Steven Schach 2002
- 53. 53 • Any type of measurement which relates to a software system, process or related documentation – Lines of code in a program, number of person-days required to develop a component • Allow the software and the software process to be quantified • Should be captured automatically and monitored if possible Software metrics ©Ian Sommerville 1995 [modified]
- 54. 54 • A quality metric should be a predictor of product quality • Most quality metrics are design quality metrics and are concerned with measuring the coupling or the complexity of a design • The relationship between these metrics and quality has to be judged by a human (no automatic connection to quality possible) • Outliers may point to problems • There are no “magic thresholds,” rather the trend of metrics over time needs to be monitored Product quality metrics ©Ian Sommerville 1995 [modified]
- 55. 55 Traditional Software Metics • Coupling metrics (associated with a structure chart in Yourdon's Structured Design) – High number of calling functions or called functions suggests high coupling • Cyclomatic complexity is a measure of control structure complexity – Metric has two drawbacks • It is inaccurate for data-driven programs as it is only concerned with control constructs. • It places the same weight on nested and non-nested loops. Deeply nested structures, however, are usually harder to understand. • Oviedo's metric modifies this to take data references into account – C = aE +bN (with N external data entities, E edges to the data entities and constants a,b) ©Ian Sommerville 1995 [modified]
- 56. 56 Metrics for Object-Oriented Software • Traditional (still usable) – Cyclomatic complexity (CC) • New OO metrics – Coupling • Coupling between objects (CBO) • Depth of inheritance tree (DIT) • … – Cohesion • Lack of cohesion of methods (LCOM) • … – Complexity • Weighted methods per class (WMC) • …
- 57. 57 • Time taken for process activities to be completed – E.g. Calendar time or effort to complete an activity or process • Resources required for processes or activities – E.g. Total effort in person-days • Number of occurrences of a particular event – E.g. Number of defects discovered • Process improvement requires process measurement! Classes of process measurement (Process Metrics) ©Ian Sommerville 1995 [modified]
- 58. 58 • Goals – What is the organisation trying to achieve? The objective of process improvement is to satisfy these goals • Questions – Questions about areas of uncertainty related to the goals. You need process knowledge to derive these • Metrics – Measurements to be collected to answer the questions Goal-Question-Metric Paradigm ©Ian Sommerville 1995 [modified]
Notes de l'éditeur
- The UML is a generic modeling language. With UML, you can produce blueprints for any kind of software system. The Rational Unified Process (RUP) is a generic process that uses UML as a modeling language. RUP can be used for any kind of software system.
- The focus of the process is the production of high-quality executables with a minimum of overhead, rather than what documents to produce. By providing a “written-down”, very detailed set of procedures for developing software according to Rational’s six best practices, the process is easier to apply and repeatable. This results in software projects that are more predicable and successful. Another feature of the Rational Unified Process is that it is not just theory. It instructs the developer on how to implement the activities using the tools the developer is using. Finally, the process is available on-line as a Website. While hardcopy books have their place, most developers prefer to reference the process from their desktops when they need help. Both hardcopy and on-line versions are available.
- Use of component-based architectures is one of the six best practices already discussed. Architecture is used in the Rational Unified Process as a primary artifact for conceptualizing, constructing, managing, and evolving the system under development. The Rational Unified Process emphasizes early development and validation of software architecture as a core concept. It defines two primary artifacts related to architecture: the Software Architecture Description (SAD) which describes the architectural views relevant to the project and the Architectural Prototype. The Rational Unified Process also defines a worker, called the Architect, who is responsible for the architecture. The bulk of the activities related to architectural design are described in the analysis and design workflow, but it spills over to the requirements workflow, the implementation workflow, and the project management workflow.
- Many different parties are interested in the architecture (e.g., the system analyst, the designers, the end uses, etc.). To allow these parties or stakeholders to communicate, discuss and reason about architecture, we need to have an architectural representation that they understand. Because different stakeholders have different concerns and because architecture is quite complex, multiple views are required to represent architecture adequately. An architectural view is a simplified description (an abstraction) of a system from a particular perspective or vantage point, covering particular concerns,and omitting entities that are not relevant to this perspective. While many views of architecture can be useful, the Rational Unified Process identifies 4+1 views as a standard set: The logical view addresses the functional requirements of the system. It is an abstraction of the design model, identifying major design packages, subsystems and classes. The implementation view describes the organization of static software modules in the development environment, in terms of packaging, layering, and configuration management. The process view addresses the concurrent aspect of the system at run-time: tasks, threads or processes, and their interactions. The deployment view shows how the various executables and other run-time components are mapped onto the underlying platforms or computing nodes. The use-case view contains a few key scenarios or use cases that are used to drive the architecture and to validate it.
- During Inception, we define the scope of the project, what is included, and what is not. This is done by identifying all the actors and use cases, and by drafting the most essential use cases (usually approximately 20% of the complete model). A business plan is developed to determine whether resources should be committed to the project. During Elaboration, we focus on two things: get a good grasp of the requirements (90% complete) and establish an architectural baseline. If we have a good grasp of the requirements and the architecture, we can eliminate a lot of the risks and will have a good idea what amount of work remains to be done. Detailed cost/resource estimations can be made at the end of Elaboration. During Construction, we build the product in several iterations up to a beta release. During Transition, we transition the product to the end user and focus on end user training, installation, and support. The amount of time spent in each phase varies. For a very complex project with a lot of technical unknowns and unclear requirements, Elaboration may include 3-5 iterations. For a very simple project where requirements are known and the architecture is simple, Elaboration may include only a single iteration.
- At each of the major milestones,the project is reviewed and a decision made as to whether to proceed with the project as planned, to abort the project, or to revise it. The criteria used to make this decision vary by phase. The evaluation criteria for the inception phase (LCO) include: stakeholder concurrence on scope definition and cost/schedule estimates; requirements understanding as evidenced by the fidelity of the primary use cases; credibility of cost/schedule estimates, priorities, risks, and development process; depth and breadth of any architectural prototype; actual expenditures versus planned expenditures. The evaluation criteria for the elaboration phase (LCA) include: stability of the product vision and architecture; resolution of major risk elements; adequate planning and reasonable estimates for project completion; stakeholder acceptance of the product vision and project plan; acceptable expenditure level. The evaluation criteria for the construction phase (IOC) include: stability and maturity of the product release (I.e., is it ready to be deployed?); readiness of the stakeholders for the transition; acceptable expenditure level. At the end of the transition phase, a decision is made whether to release the product. This will be based primarily on the level of user satisfaction achieved during the transition phase. Often this milestone coincides with the initiation of another development cycle to improve or enhance the product. In many cases, this new development cycle by already be underway.
- Within each phase, there is a series of iterations. The number of iterations per phase will vary. Each iteration results in an executable release encompassing larger and larger subsets of the final application. An internal release is kept within the development environment and (optionally) demonstrated to the stakeholder community. An external release is provided to stakeholders (usually users) for installation in their own environment. External releases are much more expensive (they require user documentation and technical support) and normally occur only during the transition phase. The end of an iteration marks a minor milestone. It is a point in time when technical results are assessed and future plans revised as necessary.
- The Rational Unified Process is a model-driven approach. Several models are needed to fully describe the evolving system. Each major workflow produces one of those models. The models are developed incrementally across iterations. The Business Model is a model of what the business processes are and the business environment. It can be used to generate requirements on supporting information systems. The Use-Case Model is a model of what the system is supposed to do and the system environment. The Design Model is an object model describing the realization of use cases. It serves as an abstraction of the implementation model and its source code. The Implementation Model is a collection of components, and the implementation subsystems that contain them. The Test Model encompasses all of the test cases and procedures required to test the system.
- This graphic illustrates how phases and iterations, or the time dimension, relates to the development activities performed, or the workflow dimension. The relative size of the color area indicates how much of the activity is performed in each phase/iteration. Each iteration involves activities from all workflows. The relative amount of work related to the workflows changes between iterations. For instance, during late Construction, the main work is related to Implementation and Test and very little work on Requirements is done. Note that requirements are not necessarily complete by the end of Elaboration. It is acceptable to delay the analysis and design of well-understood portions of the system until Construction because they are low in risk.