武汉理工软件工程课件4.ppt

1、 4.1 Phototyping in software process 4.2 Phototyping techniques 4.3 User intercase phototyping Key points Evolutionary prototyping An approach to system development where an initial prototype is produced and refined through a number of stages to the final system.Throw-away prototyping A prototype wh

2、ich is usually a practical implementation of the system is produced to help discover requirements problems and then discarded.The system is then developed using some other development process.The objective of evolutionary prototyping is to deliver a working system to end-users.The development starts

3、 with those requirements which are best understood.The objective of throw-away prototyping is to validate or derive the system requirements.The prototyping process starts with those requirements which are poorly understood.Must be used for systems where the specification cannot be developed in advan

4、ce e.g.AI systems and user interface systems.Based on techniques which allow rapid system iterations.Verification is impossible as there is no specification.Validation means demonstrating the adequacy of the system.Accelerated delivery of the system Rapid delivery and deployment are sometimes more i

5、mportant than functionality or long-term software maintainability.User engagement with the system Not only is the system more likely to meet user requirements,they are more likely to commit to the use of the system.Specification,design and implementation are inter-twined.The system is developed as a

6、 series of increments that are delivered to the customer.Techniques for rapid system development are used such as CASE tools and 4GLs.User interfaces are usually developed using a GUI development toolkit.Management problems 1.Existing management processes assume a waterfall model of development.2.Sp

7、ecialist skills are required which may not be available in all development teams.Maintenance problems Continual change tends to corrupt system structure so long-term maintenance is expensive.Contractual problems Some parts of the requirements(e.g.safety-critical functions)may be impossible to protot

8、ype and so dont appear in the specification.An implementation has no legal standing as a contract.Non-functional requirements cannot be adequately tested in a system prototype.System is developed and delivered in increments after establishing an overall architecture.Requirements and specifications f

9、or each increment may be developed.Users may experiment with delivered increments while others are being developed.therefore,these serve as a form of prototype system.Intended to combine some of the advantages of prototyping but with a more manageable process and better system structure.Used to redu

10、ce requirements risk.The prototype is developed from an initial specification,delivered for experiment then discarded.The throw-away prototype should NOT be considered as a final system.1.Some system characteristics may have been left out.2.There is no specification for long-term maintenance.3.The s

11、ystem will be poorly structured and difficult to maintain.Developers may be pressurised to deliver a throw-away prototype as a final system.This is not recommended 1.It may be impossible to tune the prototype to meet non-functional requirements.2.The prototype is inevitably undocumented.3.The system

12、 structure will be degraded through changes made during development.4.Normal organisational quality standards may not have been applied.Various techniques may be used for rapid development 1.Dynamic high-level language development.2.Database programming.3.Component and application assembly.These are

13、 not exclusive techniques-they are often used together.Visual programming is an inherent part of most prototype development systems.Languages which include powerful data management facilities.Need a large run-time support system.Not normally used for large system development.Some languages offer exc

14、ellent UI development facilities.Some languages have an integrated support environment whose facilities may be used in the prototype.What is the application domain of the problem?What user interaction is required?What support environment comes with the language?Different parts of the system may be p

15、rogrammed in different languages.However,there may be problems with language communications.Domain specific languages for business systems based around a database management system.Normally include a database query language,a screen generator,a report generator and a spreadsheet.May be integrated wi

16、th a CASE toolset.The language+environment is sometimes known as a fourth-generation language(4GL).Cost-effective for small to medium sized business systems.Prototypes can be created quickly from a set of reusable components plus some mechanism to glue these component together.The composition mechan

17、ism must include control facilities and a mechanism for component communication.The system specification must take into account the availability and functionality of existing components.Application level development 1.Entire application systems are integrated with the prototype so that their functio

18、nality can be shared.2.For example,if text preparation is required,a standard word processor can be used.Component level development 1.Individual components are integrated within a standard framework to implement the system.2.Frame work can be a scripting language or an integration framework such as

19、 CORBA For some applications,a prototype can be created by developing a compound document.This is a document with active elements(such as a spreadsheet)that allow user computations.Each active element has an associated application which is invoked when that element is selected.The document itself is

20、 the integrator for the different applications.Scripting languages such as Visual Basic support visual programming where the prototype is developed by creating a user interface from standard items and associating components with these items.A large library of components exists to support this type o

21、f development.These may be tailored to suit the specific application requirements.Difficult to coordinate team-based development.No explicit system architecture.Complex dependencies between parts of the program can cause maintainability problems.It is impossible to pre-specify the look and feel of a

22、 user interface in an effective way.prototyping is essential.UI development consumes an increasing part of overall system development costs.User interface generators may be used to draw the interface and simulate its functionality with components associated with interface entities.Web interfaces may

23、 be prototyped using a web site editor.A prototype can be used to give end-users a concrete impression of the systems capabilities.Prototyping is becoming increasingly used for system development where development is essential.Throw-away prototyping is used to understand the system requirements.In e

24、volutionary prototyping,the system is developed by evolving an initial version to the final version.Rapid development of prototypes is essential.This may require leaving out functionality or relaxing non-functional constraints.Prototyping techniques include the use of very high-level languages,database programming and prototype construction from reusable components.Prototyping is essential for parts of the system such as the user interface which cannot be effectively pre-specified.Users must be involved in prototype evaluation.