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Software EngineeringSoftware Engineering
Muhammad Fahad Muhammad Fahad KhanKhan
[email protected]@uettaxila.edu.pkkUniversity Of Engineering & University Of Engineering &
Technology Taxila,PakistanTechnology Taxila,Pakistan
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Today’s ClassToday’s Class Rapid software developmentRapid software development
chapter(17 Sommerville)chapter(17 Sommerville)
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ObjectivesObjectives
To explain how an iterative, incremental development process leads to faster delivery of more useful software
To discuss the essence of agile development methods
To explain the principles and practices of extreme programming
To explain the roles of prototyping in the software process
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Topics coveredTopics covered
Agile methodsAgile methods Extreme programmingExtreme programming Rapid application developmentRapid application development Software prototypingSoftware prototyping
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Software vs. Software vs. HardwareHardware
Because of rapidly changing business Because of rapidly changing business environments, businesses have to respond to environments, businesses have to respond to new opportunities and competition.new opportunities and competition.
This requires software and rapid development This requires software and rapid development and delivery is not often the most critical and delivery is not often the most critical requirement for software systems.requirement for software systems.
Businesses may be willing to accept lower Businesses may be willing to accept lower quality software if rapid delivery of essential quality software if rapid delivery of essential functionality is possible.functionality is possible.
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RequiremeRequirementsnts
Because of the changing environment, it is Because of the changing environment, it is often impossible to arrive at a stable, often impossible to arrive at a stable, consistent set of system requirements.consistent set of system requirements.
Therefore a waterfall model of development Therefore a waterfall model of development is impractical and an approach to is impractical and an approach to development based on iterative development based on iterative specification and delivery is the only way to specification and delivery is the only way to deliver software quickly.deliver software quickly.
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Characteristics of RAD Characteristics of RAD processesprocesses
The processes of specification, design and The processes of specification, design and implementation are concurrent. There is no detailed implementation are concurrent. There is no detailed specification and design documentation is specification and design documentation is minimized.minimized.
The system is developed in a series of increments. The system is developed in a series of increments. End users evaluate each increment and make End users evaluate each increment and make proposals for later increments.proposals for later increments.
System user interfaces are usually developed using System user interfaces are usually developed using an interactive development system.an interactive development system.
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An iterative development An iterative development processprocess
Validateincrement
Build systemincrement
Specify systemincrement
Design systemarchitecture
Define systemdeliverables
Systemcomplete?
Integrateincrement
Validatesystem
Deliver finalsystem
YES
NO
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Advantages of incremental Advantages of incremental developmentdevelopment
Accelerated delivery of customer servicesAccelerated delivery of customer services. . Each increment delivers the highest priority Each increment delivers the highest priority functionality to the customer.functionality to the customer.
User engagement with the systemUser engagement with the system. Users . Users have to be involved in the development which have to be involved in the development which means the system is more likely to meet their means the system is more likely to meet their requirements and the users are more committed requirements and the users are more committed to the system.to the system.
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Problems with incremental Problems with incremental developmentdevelopment
Management problemsManagement problems Progress can be hard to judge and problems hard to find Progress can be hard to judge and problems hard to find
because there is no documentation to demonstrate what because there is no documentation to demonstrate what has been done.has been done.
Contractual problemsContractual problems The normal contract may include a specification; without a The normal contract may include a specification; without a
specification, different forms of contract have to be used.specification, different forms of contract have to be used. Validation problemsValidation problems
Without a specification, what is the system being tested Without a specification, what is the system being tested against?against?
Maintenance problemsMaintenance problems Continual change tends to corrupt software structure Continual change tends to corrupt software structure
making it more expensive to change and evolve to meet making it more expensive to change and evolve to meet new requirements.new requirements.
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PrototypingPrototyping
For some large systems, incremental iterative For some large systems, incremental iterative development and delivery may be impractical; development and delivery may be impractical; this is especially true when multiple teams are this is especially true when multiple teams are working on different sites.working on different sites.
Prototyping, where an experimental system is Prototyping, where an experimental system is developed as a basis for formulating the developed as a basis for formulating the requirements may be used. This system is thrown requirements may be used. This system is thrown away when the system specification has been away when the system specification has been agreed.agreed.
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Incremental development and Incremental development and prototypingprototyping
Incrementaldevelopment
Throw-awayprototyping
Delivered system
Executable prototype +System specification
Outlinerequirements
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Conflicting objectivesConflicting objectives
The objective of The objective of incremental developmentincremental development is is to deliver a working system to end-users. The to deliver a working system to end-users. The development starts with those requirements development starts with those requirements which are best understood.which are best understood.
The objective of The objective of throw-away prototypingthrow-away prototyping is to is to validate or derive the system requirements. The validate or derive the system requirements. The prototyping process starts with those prototyping process starts with those requirements which are poorly understood.requirements which are poorly understood.
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Agile methodsAgile methods
Dissatisfaction with the overheads involved in design Dissatisfaction with the overheads involved in design methods led to the creation of agile methods. These methods led to the creation of agile methods. These methods:methods: Focus on user requirements rather than the designFocus on user requirements rather than the design Are based on an iterative approach to software Are based on an iterative approach to software
developmentdevelopment Are intended to deliver working software quickly Are intended to deliver working software quickly
and evolve this quickly to meet changing and evolve this quickly to meet changing requirements.requirements.
Agile methods are probably best suited to Agile methods are probably best suited to small/medium-sized business systems or PC products.small/medium-sized business systems or PC products.
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Agile methodsAgile methods
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Problems with agile methodsProblems with agile methods
It can be difficult to keep the interest of customers It can be difficult to keep the interest of customers who are involved in the process.who are involved in the process.
Team members may be unsuited to the intense Team members may be unsuited to the intense involvement that characterizes agile methods.involvement that characterizes agile methods.
Prioritizing changes can be difficult where there are Prioritizing changes can be difficult where there are multiple stakeholders.multiple stakeholders.
Maintaining simplicity requires extra work.Maintaining simplicity requires extra work.
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Types OfTypes Of Agile methodsAgile methods
Extreme programmingExtreme programming Pair programmingPair programming Visual programmingVisual programming COTS reuseCOTS reuse PrototypingPrototyping
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Extreme Extreme programmingprogramming
Perhaps the best-known and most widely used Perhaps the best-known and most widely used agile method.agile method.
Extreme Programming (XP) takes an ‘extreme’ Extreme Programming (XP) takes an ‘extreme’ approach to iterative development. approach to iterative development.
New versions may be built several times per dayNew versions may be built several times per day All tests must be run for every build and the All tests must be run for every build and the
build is only accepted if tests run successfully.build is only accepted if tests run successfully.
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Increments are delivered to customers every 2 Increments are delivered to customers every 2 weeksweeks
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The XP release cycleThe XP release cycle
Break downstories to tasks
Select userstories for this
releasePlan release
Releasesoftware
Evaluatesystem
Develop/integrate/test software
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XP and agile principlesXP and agile principles
Incremental development is supported Incremental development is supported through small, frequent system releases.through small, frequent system releases.
Customer involvement means full-time Customer involvement means full-time customer engagement with the team.customer engagement with the team.
People not process through pair People not process through pair programming, collective ownership and a programming, collective ownership and a process that avoids long working hours.process that avoids long working hours.
Change supported through regular system Change supported through regular system releases.releases.
Maintaining simplicity through constant Maintaining simplicity through constant refactoring of code.refactoring of code.
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Requirements scenariosRequirements scenarios
In XP, user requirements are expressed as In XP, user requirements are expressed as scenarios or user stories.scenarios or user stories.
These are written on cards and the These are written on cards and the development team break them down into development team break them down into implementation tasks. These tasks are the implementation tasks. These tasks are the basis of schedule and cost estimates.basis of schedule and cost estimates.
The customer chooses the stories for The customer chooses the stories for inclusion in the next release based on their inclusion in the next release based on their priorities and the schedule estimates.priorities and the schedule estimates.
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XP and changeXP and change
Conventional wisdom in software Conventional wisdom in software engineering is to design for change. It is engineering is to design for change. It is worth spending time and effort worth spending time and effort anticipating changes as this reduces anticipating changes as this reduces costs later in the life cycle.costs later in the life cycle.
Rather, it proposes constant code Rather, it proposes constant code improvement (refactoring) to make improvement (refactoring) to make changes easier when they have to be changes easier when they have to be implemented.implemented.
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Testing in XPTesting in XP
Test-first development.Test-first development. Incremental test development from Incremental test development from
scenarios.scenarios. User involvement in test development and User involvement in test development and
validation.validation. Automated test harnesses are used to run all Automated test harnesses are used to run all
component tests each time that a new component tests each time that a new release is built.release is built.
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Test-first developmentTest-first development
Writing tests before code clarifies the Writing tests before code clarifies the requirements to be implemented.requirements to be implemented.
Tests are written as programs rather than data so Tests are written as programs rather than data so that they can be executed automatically. The test that they can be executed automatically. The test includes a check that it has executed correctly.includes a check that it has executed correctly.
All previous and new tests are automatically run All previous and new tests are automatically run when new functionality is added. Thus checking when new functionality is added. Thus checking that the new functionality has not introduced that the new functionality has not introduced errors.errors.
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Pair Pair programmingprogramming
In XP, programmers work in pairs, sitting together In XP, programmers work in pairs, sitting together to develop code.to develop code.
This helps develop common ownership of code This helps develop common ownership of code and spreads knowledge across the team.and spreads knowledge across the team.
It serves as an informal review process as each It serves as an informal review process as each line of code is looked at by more than 1 person.line of code is looked at by more than 1 person.
It encourages refactoring as the whole team can It encourages refactoring as the whole team can benefit from this.benefit from this.
Measurements suggest that development Measurements suggest that development productivity with pair programming is similar to productivity with pair programming is similar to that of two people working independently.that of two people working independently.
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Rapid application Rapid application developmentdevelopment
Agile methods have received a lot of attention but Agile methods have received a lot of attention but other approaches to rapid application other approaches to rapid application development have been used for many years.development have been used for many years.
These are designed to develop data-intensive These are designed to develop data-intensive business applications and rely on programming business applications and rely on programming and presenting information from a database.and presenting information from a database.
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RAD environment RAD environment toolstools
Database programming languageDatabase programming language Interface generatorInterface generator Links to office applicationsLinks to office applications Report generatorsReport generators
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A RAD environmentA RAD environment
DBprogramming
language
Interfacegenerator
Officesystems
Reportgenerator
Database management system
Rapid applicationdevelopment environment
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Interface generationInterface generation
Many applications are based around Many applications are based around complex forms and developing these forms complex forms and developing these forms manually is a time-consuming activity.manually is a time-consuming activity.
RAD environments include support for RAD environments include support for screen generation including:screen generation including: Interactive form definition using drag and Interactive form definition using drag and
drop techniques.drop techniques. Form linking where the sequence of forms Form linking where the sequence of forms
to be presented is specified.to be presented is specified. Form verification where allowed ranges in Form verification where allowed ranges in
form fields is defined.form fields is defined.
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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 prototype is developed by creating a user interface from standard items and user interface from standard items and associating components with these associating components with these itemsitems
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 These may be tailored to suit the specific application requirementsspecific application requirements
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Problems with visual Problems with visual developmentdevelopment
Difficult to coordinate team-based development.Difficult to coordinate team-based development. No explicit system architecture.No explicit system architecture. Complex dependencies between parts of the Complex dependencies between parts of the
program can cause maintainability problems.program can cause maintainability problems.
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COTS reuseCOTS reuse
An effective approach to rapid development is to An effective approach to rapid development is to configure and link existing off the shelf systems.configure and link existing off the shelf systems.
For example, a requirements management For example, a requirements management system could be built by using:system could be built by using: A database to store requirements.A database to store requirements. A word processor to capture requirements and A word processor to capture requirements and
format reports.format reports. A spreadsheet for traceability management.A spreadsheet for traceability management.
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Compound documentsCompound documents
For some applications, a prototype can be For some applications, a prototype can be created by developing a compound document.created by developing a compound document.
This is a document with active elements (such as This is a document with active elements (such as a spreadsheet) that allow user computations.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 is application which is invoked when that element is selected.selected.
The document itself is the integrator for the The document itself is the integrator for the different applications.different applications.
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Application linkingApplication linking
Word processor Spreadsheet Audio player
Text 1 Text 2 Text 3
Text 5
Table 1 Sound 1
Text 4Table 2 Sound 2
Compound document
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Software prototypingSoftware prototyping
A prototype is an initial version of a system used A prototype is an initial version of a system used to demonstrate concepts and try out design to demonstrate concepts and try out design options.options.
A prototype can be used in:A prototype can be used in: The requirements engineering process to help The requirements engineering process to help
with requirements elicitation and validation.with requirements elicitation and validation. In design processes to explore options and In design processes to explore options and
develop a UI design.develop a UI design. In the testing process to run back-to-back In the testing process to run back-to-back
tests.tests.
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Benefits of prototypingBenefits of prototyping
Improved system usability.Improved system usability. A closer match to users’ real needs.A closer match to users’ real needs. Improved design quality.Improved design quality. Improved maintainability.Improved maintainability. Reduced development effort.Reduced development effort.
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Back to back testingBack to back testingTest data
Resultscomparator
Systemprototype
Applicationsystem
Differencereport
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The prototyping processThe prototyping process
Establishprototypeobjectives
Defineprototype
functionality
Developprototype
Evaluateprototype
Prototypingplan
Outlinedefinition
Executableprototype
Evaluationreport
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Throw-away prototypesThrow-away prototypes
Prototypes should be discarded after Prototypes should be discarded after development as they are not a good basis for a development as they are not a good basis for a production system:production system: It may be impossible to tune the system to It may be impossible to tune the system to
meet non-functional requirements.meet non-functional requirements. Prototypes are normally undocumented.Prototypes are normally undocumented. The prototype structure is usually degraded The prototype structure is usually degraded
through rapid change.through rapid change. The prototype probably will not meet normal The prototype probably will not meet normal
organizational quality standards.organizational quality standards.
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Key pointsKey points
An iterative approach to software development An iterative approach to software development leads to faster delivery of software.leads to faster delivery of software.
Agile methods are iterative development methods Agile methods are iterative development methods that aim to reduce development overhead and so that aim to reduce development overhead and so produce software faster.produce software faster.
Extreme programming includes practices such as Extreme programming includes practices such as systematic testing, continuous improvement and systematic testing, continuous improvement and customer involvement.customer involvement.
The approach to testing in XP is a particular The approach to testing in XP is a particular strength where executable tests are developed strength where executable tests are developed before the code is written.before the code is written.
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Key pointsKey points
Rapid application development environments Rapid application development environments include database programming languages, form include database programming languages, form generation tools and links to office applications.generation tools and links to office applications.
A throw-away prototype is used to explore A throw-away prototype is used to explore requirements and design options.requirements and design options.
When implementing a throw-away prototype, When implementing a throw-away prototype, start with the requirements you least understand; start with the requirements you least understand; in incremental development, start with the best-in incremental development, start with the best-understood requirements.understood requirements.
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Question & Review session
For any query feel free to contact For any query feel free to contact [email protected]@uettaxila.edu.pk
