Download - Software Prototyping
Software PrototypingSoftware Prototyping
Rapid software Rapid software development to validate development to validate requirementsrequirements
ObjectivesObjectives To describe the use of prototypes in different To describe the use of prototypes in different
types of development projecttypes of development project To discuss evolutionary and throw-away To discuss evolutionary and throw-away
prototypingprototyping To introduce three rapid prototyping To introduce three rapid prototyping
techniques - high-level language development, techniques - high-level language development, database programming and component reusedatabase programming and component reuse
To explain the need for user interface To explain the need for user interface prototypingprototyping
Topics coveredTopics covered Prototyping in the software processPrototyping in the software process Prototyping techniquesPrototyping techniques User interface prototypingUser interface prototyping
System prototypingSystem prototyping Prototyping is the rapid development of a systemPrototyping is the rapid development of a system In the past, the developed system was normally In the past, the developed system was normally
thought of as inferior in some way to the required thought of as inferior in some way to the required system so further development was requiredsystem so further development was required
Now, the boundary between prototyping and Now, the boundary between prototyping and normal system development is blurred and many normal system development is blurred and many systems are developed using an evolutionary systems are developed using an evolutionary approachapproach
Uses of system prototypesUses of system prototypes The principal use is to help customers and The principal use is to help customers and
developers understand the requirements for the developers understand the requirements for the systemsystem Requirements elicitation. Users can experiment with a Requirements elicitation. Users can experiment with a
prototype to see how the system supports their workprototype to see how the system supports their work Requirements validation. The prototype can reveal Requirements validation. The prototype can reveal
errors and omissions in the requirementserrors and omissions in the requirements
Prototyping can be considered as a risk reduction Prototyping can be considered as a risk reduction activity which reduces requirements risksactivity which reduces requirements risks
Prototyping benefitsPrototyping benefits Misunderstandings between software Misunderstandings between software
users and developers are exposedusers and developers are exposed Missing services may be detected and Missing services may be detected and
confusing services may be identifiedconfusing services may be identified A working system is available early in the A working system is available early in the
processprocess The prototype may serve as a basis for The prototype may serve as a basis for
deriving a system specificationderiving a system specification The system can support user training and The system can support user training and
system testingsystem testing
Prototyping processPrototyping process
Establishprototypeobjectives
Defineprototype
functionality
Developprototype
Evaluateprototype
Prototypingplan
Outlinedefinition
Executableprototype
Evaluationreport
Prototyping benefitsPrototyping benefits
Improved system usabilityImproved system usability Closer match to the system neededCloser match to the system needed Improved design qualityImproved design quality Improved maintainabilityImproved maintainability Reduced overall development effortReduced overall development effort
Prototyping in the Prototyping in the software processsoftware process Evolutionary prototypingEvolutionary prototyping
An approach to system development where an initial An approach to system development where an initial prototype is produced and refined through a number of prototype is produced and refined through a number of stages to the final systemstages to the final system
Throw-away prototypingThrow-away prototyping A prototype which is usually a practical implementation A prototype which is usually a practical implementation
of the system is produced to help discover requirements of the system is produced to help discover requirements problems and then discarded. The system is then problems and then discarded. The system is then developed using some other development processdeveloped using some other development process
Prototyping objectivesPrototyping objectives The objective of The objective of evolutionary prototypingevolutionary prototyping is is
to deliver a working system to end-users. to deliver a working system to end-users. The development starts with those The development starts with those requirements which are best understood.requirements which are best understood.
The objective of The objective of throw-away prototypingthrow-away prototyping is is to validate or derive the system to validate or derive the system requirements. The prototyping process requirements. The prototyping process starts with those requirements which are starts with those requirements which are poorly understoodpoorly understood
Approaches to Approaches to prototypingprototyping
Evolutionaryprototyping
Throw-awayPrototyping
Deliveredsystem
Executable Prototype +System Specification
OutlineRequirements
Evolutionary prototypingEvolutionary prototyping Must be used for systems where the Must be used for systems where the
specification cannot be developed in specification cannot be developed in advance e.g. AI systems and user interface advance e.g. AI systems and user interface systemssystems
Based on techniques which allow rapid Based on techniques which allow rapid system iterationssystem iterations
Verification is impossible as there is no Verification is impossible as there is no specification. Validation means specification. Validation means demonstrating the adequacy of the systemdemonstrating the adequacy of the system
Evolutionary prototypingEvolutionary prototyping
Build prototypesystem
Develop abstractspecification
Use prototypesystem
Deliversystem
Systemadequate?
YES
N
Evolutionary prototyping Evolutionary prototyping advantagesadvantages
Accelerated delivery of the systemAccelerated delivery of the system Rapid delivery and deployment are Rapid delivery and deployment are
sometimes more important than functionality sometimes more important than functionality or long-term software maintainabilityor long-term software maintainability
User engagement with the systemUser engagement with the system Not only is the system more likely to meet Not only is the system more likely to meet
user requirements, they are more likely to user requirements, they are more likely to commit to the use of the systemcommit to the use of the system
Evolutionary prototypingEvolutionary prototyping
Specification, design and implementation are Specification, design and implementation are inter-twinedinter-twined
The system is developed as a series of The system is developed as a series of increments that are delivered to the customerincrements that are delivered to the customer
Techniques for rapid system development are Techniques for rapid system development are used such as CASE tools and 4GLsused such as CASE tools and 4GLs
User interfaces are usually developed using a User interfaces are usually developed using a GUI development toolkitGUI development toolkit
Evolutionary prototyping Evolutionary prototyping problemsproblems
Management problemsManagement problems Existing management processes assume a Existing management processes assume a
waterfall model of developmentwaterfall model of development Specialist skills are required which may not be Specialist skills are required which may not be
available in all development teamsavailable in all development teams
Maintenance problemsMaintenance problems Continual change tends to corrupt system Continual change tends to corrupt system
structure so long-term maintenance is expensivestructure so long-term maintenance is expensive
Contractual problemsContractual problems
Prototypes as Prototypes as specificationsspecifications
Some parts of the requirements (e.g. Some parts of the requirements (e.g. safety-critical functions) may be safety-critical functions) may be impossible to prototype and so don’t impossible to prototype and so don’t appear in the specificationappear in the specification
An implementation has no legal standing An implementation has no legal standing as a contractas a contract
Non-functional requirements cannot be Non-functional requirements cannot be adequately tested in a system prototypeadequately tested in a system prototype
Incremental developmentIncremental development System is developed and delivered in increments System is developed and delivered in increments
after establishing an overall architectureafter establishing an overall architecture Requirements and specifications for each increment Requirements and specifications for each increment
may be developedmay be developed Users may experiment with delivered increments Users may experiment with delivered increments
while others are being developed. therefore, these while others are being developed. therefore, these serve as a form of prototype systemserve as a form of prototype system
Intended to combine some of the advantages of Intended to combine some of the advantages of prototyping but with a more manageable process prototyping but with a more manageable process and better system structureand better system structure
Incremental development Incremental development processprocess
Validateincrement
Build systemincrement
Specify systemincrement
Design systemarchitecture
Define systemdeliverables
Systemcomplete?
Integrateincrement
Validatesystem
Deliver finalsystem
YES
NO
Throw-away prototypingThrow-away prototyping Used to reduce requirements riskUsed to reduce requirements risk The prototype is developed from an initial The prototype is developed from an initial
specification, delivered for experiment then specification, delivered for experiment then discardeddiscarded
The throw-away prototype should NOT be The throw-away prototype should NOT be considered as a final systemconsidered as a final system Some system characteristics may have been left outSome system characteristics may have been left out There is no specification for long-term maintenanceThere is no specification for long-term maintenance The system will be poorly structured and difficult to The system will be poorly structured and difficult to
maintainmaintain
Throw-away prototypingThrow-away prototypingOutline
requirementsDevelopprototype
Evaluateprototype
Specifysystem
Developsoftware
Validatesystem
Deliveredsoftwaresystem
Reusablecomponents
Prototype deliveryPrototype delivery
Developers may be pressurised to deliver a Developers may be pressurised to deliver a throw-away prototype as a final systemthrow-away prototype as a final system
This is not recommendedThis is not recommended It may be impossible to tune the prototype to meet It may be impossible to tune the prototype to meet
non-functional requirementsnon-functional requirements The prototype is inevitably undocumentedThe prototype is inevitably undocumented The system structure will be degraded through The system structure will be degraded through
changes made during developmentchanges made during development Normal organisational quality standards may not Normal organisational quality standards may not
have been appliedhave been applied
Rapid prototyping Rapid prototyping techniquestechniques
Various techniques may be used for rapid Various techniques may be used for rapid developmentdevelopment Dynamic high-level language developmentDynamic high-level language development Database programmingDatabase programming Component and application assemblyComponent and application assembly
These are not exclusive techniques - they are These are not exclusive techniques - they are often used togetheroften used together
Visual programming is an inherent part of Visual programming is an inherent part of most prototype development systemsmost prototype development systems
Dynamic high-level Dynamic high-level languageslanguages
Languages which include powerful data Languages which include powerful data management facilitiesmanagement facilities
Need a large run-time support system. Not Need a large run-time support system. Not normally used for large system developmentnormally used for large system development
Some languages offer excellent UI Some languages offer excellent UI development facilitiesdevelopment facilities
Some languages have an integrated support Some languages have an integrated support environment whose facilities may be used in environment whose facilities may be used in the prototypethe prototype
Prototyping languagesPrototyping languages
Choice of prototyping Choice of prototyping languagelanguage
What is the application domain of the What is the application domain of the problem?problem?
What user interaction is required?What user interaction is required? What support environment comes with the What support environment comes with the
language?language? Different parts of the system may be Different parts of the system may be
programmed in different languages. However, programmed in different languages. However, there may be problems with language there may be problems with language communicationscommunications
Database programming Database programming languageslanguages
Domain specific languages for business systems Domain specific languages for business systems based around a database management systembased around a database management system
Normally include a database query language, a Normally include a database query language, a screen generator, a report generator and a screen generator, a report generator and a spreadsheet. spreadsheet.
May be integrated with a CASE toolsetMay be integrated with a CASE toolset The language + environment is sometimes known The language + environment is sometimes known
as a fourth-generation language (4GL)as a fourth-generation language (4GL) Cost-effective for small to medium sized business Cost-effective for small to medium sized business
systemssystems
Database programmingDatabase programming
DBprogramming
language
Interfacegenerator Spreadsheet
Reportgenerator
Database management system
Fourth-generation language
Component and application Component and application assemblyassembly
Prototypes can be created quickly from a set Prototypes can be created quickly from a set of reusable components plus some of reusable components plus some mechanism to ‘glue’ these component togethermechanism to ‘glue’ these component together
The composition mechanism must include The composition mechanism must include control facilities and a mechanism for control facilities and a mechanism for component communicationcomponent communication
The system specification must take into The system specification must take into account the availability and functionality of account the availability and functionality of existing componentsexisting components
Prototyping with reusePrototyping with reuse Application level developmentApplication level development
Entire application systems are integrated with the Entire application systems are integrated with the prototype so that their functionality can be sharedprototype so that their functionality can be shared
For example, if text preparation is required, a For example, if text preparation is required, a standard word processor can be usedstandard word processor can be used
Component level developmentComponent level development Individual components are integrated within a Individual components are integrated within a
standard framework to implement the systemstandard framework to implement the system Frame work can be a scripting language or an Frame work can be a scripting language or an
integration framework such as CORBAintegration framework such as CORBA
Reusable component Reusable component compositioncomposition
Componentcompositionframework
Executableprototype
Reusablesoftware
components
Control andintegration code
Compound documentsCompound documents For some applications, a prototype can be For some applications, a prototype can be
created by developing a compound documentcreated by developing a compound document This is a document with active elements (such This is a document with active elements (such
as a spreadsheet) that allow user computationsas a spreadsheet) that allow user computations Each active element has an associated Each active element has an associated
application which is invoked when that element application which is invoked when that element is selectedis selected
The document itself is the integrator for the The document itself is the integrator for the different applicationsdifferent applications
Application linking in compound Application linking in compound documentsdocuments
Compound document
Word processor Spreadsheet Audio player
Text 1 Text 2 Text 3
Text 4 Text 5
Table 1
Table 2
Sound 1
Sound 2
Visual programmingVisual programming
Scripting languages such as Visual Basic Scripting languages such as Visual Basic support visual programming where the support visual programming where the prototype is developed by creating a user prototype is developed by creating a user interface from standard items and interface from standard items and associating components with these itemsassociating components with these items
A large library of components exists to A large library of components exists to support this type of developmentsupport this type of development
These may be tailored to suit the specific These may be tailored to suit the specific application requirementsapplication requirements
Visual programming with Visual programming with reusereuse
File Edit Views Layout Options Help
GeneralIndex
Hypertextdisplay componentDate component
Range checkingscript
Tree displaycomponent
12th January 2000
3.876
Draw canvascomponent
User promptcomponent +
script
Problems with visual Problems with visual developmentdevelopment
Difficult to coordinate team-based Difficult to coordinate team-based developmentdevelopment
No explicit system architectureNo explicit system architecture Complex dependencies between parts of Complex dependencies between parts of
the program can cause maintainability the program can cause maintainability problemsproblems
User interface User interface prototypingprototyping
It is impossible to pre-specify the look and feel of a It is impossible to pre-specify the look and feel of a user interface in an effective way. prototyping is user interface in an effective way. prototyping is essentialessential
UI development consumes an increasing part of UI development consumes an increasing part of overall system development costsoverall system development costs
User interface generators may be used to ‘draw’ User interface generators may be used to ‘draw’ the interface and simulate its functionality with the interface and simulate its functionality with components associated with interface entitiescomponents associated with interface entities
Web interfaces may be prototyped using a web Web interfaces may be prototyped using a web site editorsite editor
Key pointsKey points A prototype can be used to give end-users a A prototype can be used to give end-users a
concrete impression of the system’s capabilitiesconcrete impression of the system’s capabilities Prototyping is becoming increasingly used for Prototyping is becoming increasingly used for
system development where rapid development is system development where rapid development is essentialessential
Throw-away prototyping is used to understand the Throw-away prototyping is used to understand the system requirementssystem requirements
In evolutionary prototyping, the system is In evolutionary prototyping, the system is developed by evolving an initial version to the final developed by evolving an initial version to the final versionversion
Key pointsKey points Rapid development of prototypes is essential. This Rapid development of prototypes is essential. This
may require leaving out functionality or relaxing may require leaving out functionality or relaxing non-functional constraintsnon-functional constraints
Prototyping techniques include the use of very Prototyping techniques include the use of very high-level languages, database programming and high-level languages, database programming and prototype construction from reusable componentsprototype construction from reusable components
Prototyping is essential for parts of the system Prototyping is essential for parts of the system such as the user interface which cannot be such as the user interface which cannot be effectively pre-specified. Users must be involved in effectively pre-specified. Users must be involved in prototype evaluationprototype evaluation