软件工程评估和管理英文讲义process3.ppt

1、CSEM01 - Wk 3 - Process,1,Software Processes,CSEM01 SE Evolution Requirements elicitation and analysis; Requirements specification; Requirements validation.,CSEM01 - Wk 3 - Process,6,The requirements engineering process,CSEM01 - Wk 3 - Process,7,Software design and implementation,The process of conv

2、erting the system specification into an executable system. Software design Design a software structure that realises the specification; Implementation Translate this structure into an executable program; The activities of design and implementation are closely related and may be inter-leaved,CSEM01 -

3、 Wk 3 - Process,8,Design process activities,Architectural design Abstract specification Interface design Component design Data structure design Algorithm design,CSEM01 - Wk 3 - Process,9,The software design process,CSEM01 - Wk 3 - Process,10,Structured methods,Systematic approaches to developing a s

4、oftware design. The design is usually documented as a set of graphical models. Possible models Object model; Sequence model; State transition model; Structural model; Data-flow model.,CSEM01 - Wk 3 - Process,11,Programming and debugging,Translating a design into a program and removing errors from th

5、at program. Programming is a personal activity - there is no generic programming process. Programmers carry out some program testing to discover faults in the program and remove these faults in the debugging process.,CSEM01 - Wk 3 - Process,12,The debugging process,Locate,error,Design,error,repair,R

6、epair,error,Re-test,program,CSEM01 - Wk 3 - Process,13,Software validation,Verification and validation (V Components may be functions or objects or coherent groupings of these entities. System testing Testing of the system as a whole. Testing of emergent properties is particularly important. Accepta

7、nce testing Testing with customer data to check that the system meets the customers needs.,CSEM01 - Wk 3 - Process,16,Testing phases,R,equir,ements,specifica,tion,S,ystem,specifica,tion,S,ystem,design,Detailed,design,Module and,unit code,and test,Sub-system,integ,r,a,tion,test plan,S,ystem,integ,r,a

8、,tion,test plan,Acceptance,test plan,Service,Acceptance,test,S,ystem,integ,r,a,tion test,Sub-system,integ,r,a,tion test,CSEM01 - Wk 3 - Process,17,Software evolution,Software is inherently flexible and can change. As requirements change through changing business circumstances, the software that supp

9、orts the business must also evolve and change. Although there has been a demarcation between development and evolution (maintenance) this is increasingly irrelevant as fewer and fewer systems are completely new.,CSEM01 - Wk 3 - Process,18,System evolution,CSEM01 - Wk 3 - Process,19,Mid point review,

10、The software process A structured set of activities required to develop a software system Specification; Design; Validation; Evolution. A software process model an abstract representation of a process. It presents a description of a process from some particular perspective.,CSEM01 - Wk 3 - Process,2

11、0,Generic software process models,The waterfall model Separate and distinct phases of specification and development. Evolutionary development Specification, development and validation are interleaved. Component-based software engineering The system is assembled from existing components. There are ma

12、ny variants of these models e.g. formal development where a waterfall-like process is used but the specification is a formal specification that is refined through several stages to an implementable design.,CSEM01 - Wk 3 - Process,21,Waterfall model,Requirements,definition,System and,software design,

13、Implementation,and unit testing,Integration and,system testing,Operation and,maintenance,CSEM01 - Wk 3 - Process,22,Waterfall model problems,The difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase. Inflexible partitioning o

14、f the project into distinct stages - so it is then difficult to respond to changing customer requirements. Only appropriate when the requirements are well understood; changes will be fairly limited during the design process. Few business systems have stable requirements.,CSEM01 - Wk 3 - Process,23,E

15、volutionary development,Exploratory development Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements and add new features as proposed by the customer. Throw-away prototyping Objective is to understand t

16、he system requirements. Should start with poorly understood requirements to clarify what is really needed.,CSEM01 - Wk 3 - Process,24,Evolutionary development,CSEM01 - Wk 3 - Process,25,Evolutionary development,Problems Lack of process visibility; Systems are often poorly structured; Special skills

17、(e.g. in languages for rapid prototyping) may be required. Applicability For small or medium-size interactive systems; For parts of large systems (e.g. the user interface); For short-lifetime systems.,CSEM01 - Wk 3 - Process,26,Component-based software engineering,Based on systematic reuse where sys

18、tems are integrated from existing components or COTS (Commercial-off-the-shelf) systems. Process stages Component analysis; Requirements modification; System design with reuse; Development and integration. This approach is becoming increasingly used as component standards have emerged.,CSEM01 - Wk 3

19、 - Process,27,Reuse-oriented development,CSEM01 - Wk 3 - Process,28,Process iteration,System requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems. Iteration can be applied to any of the generic pr

20、ocess models. Two (related) approaches Incremental delivery; Spiral development.,CSEM01 - Wk 3 - Process,29,Incremental delivery,Rather than deliver the system as a single delivery, the development and delivery is broken down into increments with each increment delivering part of the required functi

21、onality. User requirements are prioritised and the highest priority requirements are included in early increments. Once the development of an increment is started, the requirements are frozen though requirements for later increments can continue to evolve.,CSEM01 - Wk 3 - Process,30,Incremental deve

22、lopment,CSEM01 - Wk 3 - Process,31,Incremental development advantages,Customer value can be delivered with each increment so system functionality is available earlier. Early increments act as a prototype to help elicit requirements for later increments. Lower risk of overall project failure. The hig

23、hest priority system services tend to receive the most testing.,CSEM01 - Wk 3 - Process,32,Extreme programming,An approach to development based on the development and delivery of very small increments of functionality. Relies on constant code improvement, user involvement in the development team, pa

24、ir programming,and frequent build.,CSEM01 - Wk 3 - Process,33,Spiral development,Process is represented as a spiral rather than as a sequence of activities with backtracking. Each loop in the spiral represents a phase in the process. No fixed phases such as specification or design - loops in the spi

25、ral are chosen depending on what is required. Risks are explicitly assessed and resolved throughout the process.,CSEM01 - Wk 3 - Process,34,Spiral model - Boehm,CSEM01 - Wk 3 - Process,35,Spiral model sectors,Objective setting Specific objectives for the phase are identified. Risk assessment and red

26、uction Risks are assessed and activities put in place to reduce the key risks. Development and validation A development model for the system is chosen which can be any of the generic models. Planning The project is reviewed and the next phase of the spiral is planned.,CSEM01 - Wk 3 - Process,36,The

27、Rational Unified Process,A modern process model derived from the work on the UML and associated process. Normally described from 3 perspectives A dynamic perspective that shows phases over time; A static perspective that shows process activities; A practive perspective that suggests good practice.,C

28、SEM01 - Wk 3 - Process,37,RUP phases,Inception Establish the business case for the system. Elaboration Develop an understanding of the problem domain and the system architecture. Construction System design, programming and testing. Transition Deploy the system in its operating environment.,CSEM01 -

29、Wk 3 - Process,38,RUP good practice,Develop software iteratively Manage requirements Use component-based architectures Visually model software Verify software quality Control changes to software,CSEM01 - Wk 3 - Process,39,The SEI process maturity model,CSEM01 - Wk 3 - Process,40,Key process areas,CS

30、EM01 - Wk 3 - Process,41,It focuses on project management rather than product development. It ignores the use of technologies such as rapid prototyping. It does not incorporate risk analysis as a key process area It does not define its domain of applicability,SEI model problems,CSEM01 - Wk 3 - Proce

31、ss,42,Wherever possible, quantitative process data should be collected Very difficult where organisations dont have clearly defined process standards, as you dont know what to measure - a process may have to be defined before any measurement is possible. Process measurements should be used to assess

32、 process improvements The improvements driver is the organizational objectives, not the measurements.,Process measurement,CSEM01 - Wk 3 - Process,43,Time taken for process activities to be completed - e.g. Calendar time or effort to complete an activity or process. Resources required for processes o

33、r activities - e.g. Total effort in person-days. Number of occurrences of a particular event - e.g. Number of defects discovered.,Classes of process measurement,CSEM01 - Wk 3 - Process,44,Key points,Software processes are the activities involved in producing and evolving a software system. Software process models are a