Lesson 18

Software DevelopmentSoftware Development

W.C.UduwelaDepartment of Mathematics and Computer

Science

Why Rapid S/W DevelopmentWhy Rapid S/W Development

• Because of rapidly changing business environments, businesses have to respond to new opportunities and competition.

• Businesses may be willing to accept lower quality • Businesses may be willing to accept lower quality software if rapid delivery of essential functionality is possible.

Cont…Cont…

• Because of the changing environment, it is often impossible to arrive at a stable, consistent set of system requirements.

• Therefore a waterfall model of development is • Therefore a waterfall model of development is impractical and an approach to developmentbased on iterative specification and delivery is the only way to deliver software quickly.

What are the characteristics of rapid What are the characteristics of rapid S/W S/W development?development?

• The processes of specification, design and implementation are concurrent. There is no detailed specification and design documentation is minimized.is minimized.

• The system is developed in a series of increments. End users evaluate each increment and make proposals for later increments.

• System user interfaces are usually developed using an interactive development system.

Incremental Incremental development processdevelopment process

ValidateBuild systemSpecify systemDesign system

Define systemdeliverab les

Validateincrement

Build systemincrement

Specify systemincrement

Design systemarchitectur e

System

complete?Integ rate

increment

Valida te

system

Deliver final

systemYES

NO

Advantages of incremental developmentAdvantages of incremental development

• Accelerated delivery of customer services. Each increment delivers the highest priority functionality to the customer.

• User engagement with the system. Users have • User engagement with the system. Users have to be involved in the development which means the system is more likely to meet their requirements and the users are more committed to the system.

Problems with incremental developmentProblems with incremental development

• Management problems– Progress can be hard to judge and problems hard to find because

there is no documentation to demonstrate what has been done.

• Contractual 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.

• Validation problems– Without a specification, what is the system being tested against?

• Maintenance problems– Continual change tends to corrupt software structure making it more

expensive to change and evolve to meet new requirements.

Prototyping in incremental developmentPrototyping in incremental development

• For some large systems, incremental iterative development and delivery may be impractical; this is especially true when multiple teams are working on different sites.

• Prototyping, where an experimental system is developed as a basis for formulating the requirements may be used. This system is thrown away when the system specification has been agreed.

Conflicting objectivesConflicting objectives

• The objective of incremental development is to deliver a working system to end-users. The development starts with those requirements which are best understood.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.

Agile methodsAgile methods

• Dissatisfaction with the overheads involved in design methods led to the creation of agile methods. These methods:– Focus on the code rather than the design;

– Are based on an iterative approach to software development;development;

– Are intended to deliver working software quickly and evolve this quickly to meet changing requirements.

• Agile methods are probably best suited to small/medium-sized business systems or PC products.

Principles of agile methodsPrinciples of agile methods

Principle Description

Customer involvement The customer should be closely involved throughout the development process. Their role is provide and prioritise new system requirements and to evaluate the iterations of the system.

Incremental delivery The software is developed in increments with the customer specifying the requirements to be included in each increment. specifying the requirements to be included in each increment.

People not process The skills of the development team should be recognised and exploited. The team should be left to develop their own ways of working without prescriptive processes.

Embrace change Expect the system requirements to change and design the system so that it can accommodate these changes.

Maintain simplicity Focus on simplicity in both the software being developed and in the development process used. Wherever possible, actively work to eliminate complexity from the system.

Extreme programmingExtreme programming

• Perhaps the best-known and most widely used agile method.

• Extreme Programming (XP) takes an ‘extreme’ approach to iterative development. approach to iterative development. – New versions may be built several times per day;

– Increments are delivered to customers every 2 weeks;

– All tests must be run for every build and the build is only accepted if tests run successfully.

The XP release cycleThe XP release cycle

Break downstories to tasks

Select userstories for this

release

Plan release

Release

software

Evaluatesystem

Develop/integ rate/

test software

Extreme programming practices 1Extreme programming practices 1

Incremental planning Requirements are recorded on Story Cards and the Stories to beincluded in a release are determined by the time available andtheir relative priority. The developers break these Stories intodevelopment ŌTasksÕ.

Small Releases The minimal useful set of functionality that provides businessvalue is developed first. Releases of the system are frequent andincrementally add functionality to the first release.incrementally add functionality to the first release.

Simple Design Enough design is carried out to meet the current requirementsand no more.

Test first development An automated unit test framework is used to write tests for a newpiece of functionality before that functionality itself isimplemented.

Refactoring All developers are expected to refactor the code con tinuously assoon as possible code improvements are found. This keeps thecode simple and maintainable.

Extreme programming practices 2Extreme programming practices 2

Pair Programming Developers work in pairs, checking each otherÕs work andproviding the support to always do a good job.

Collective Ownership The pairs of developers work on all areas of the system, so thatno islands of expertise develop and all the developers own all thecode. Anyone can change anything.

Continuous Integration As soon as work on a task is complete it is integrated into theContinuous Integration As soon as work on a task is complete it is integrated into thewhole system. After any such integration, all the unit tests in thesystem must pass.

Sustainable pace Large amounts of over-time are not considered acceptable as thenet effect is often to reduce code qua lity and medium termproductivity

On-site Customer A representative of the end-user of the system (the Customer)should be available full time for the use of the XP team. In anextreme programming process, the customer is a member of thedevelopment team and is responsible for bringing systemrequirements to the team for implementation.

StoryStory card for document downloadingcard for document downloading

Downloading and printing an article

First, you select the article that you want from a displayed list. Youthen have to tell the system how you will pay for it - this can eitherbe through a subscription, through a company account or by creditcard.card.

After this, you get a copyright form from the system to fill in and,when you have submitted this, the article you want is downloadedonto your computer .

You then choose a printer and a copy of the article is printed. Youtell the system if printing has been successful.

If the article is a print-only article, you canÕ t keep the PDF versionso it is automatically deleted from your computer .

Rapid Rapid Application DevelopmentApplication Development

• Agile methods have received a lot of attention but other approaches to rapid application development have been used for many years.

• These are designed to develop data-intensive business applications and rely on programming and presenting information from a database.

RAD environment toolsRAD environment tools

• Database programming language

• Interface generator

• Links to office applications

• Report generators• Report generators

Design PatternsDesign Patterns

• What are Design Patterns?– A Software design pattern provides us a general solution to

a common problem in software design.– It is a description or template for how to solve a problem. – Patterns provide us reusable solutions to commonly

encountered programming challengesencountered programming challenges– This helps us speed up the Design and overall

Development Time and Effort thereby resulting in cost savings.

– since these patterns are time tested they provide solutions with known benefits and drawbacks

– Over a period of time patterns get improvised and new patterns emerge.

Cont…Cont…

• Creational patterns:

– Creational design patterns deal with object creation mechanisms

– Factory Design– Factory Design

• focuses on how the objects are created

Cont…Cont…

• Structural Patterns

• Behavioral Patterns

Lesson 27

Rapid Application DevelopmentRapid Application Development(RAD)(RAD)(RAD)(RAD)

W.C.UduwelaDepartment of Mathematics and Computer

Science

IntroductionIntroduction

“Rapid Application Development (RAD) is

a development lifecycle designed to give much faster development and higher-quality resultsthan those achieved with the traditional lifecycle. than those achieved with the traditional lifecycle. It is designed to take the maximum advantage of powerful development software that has evolved recently.”

James Martin

ContCont……

“an approach to building computer systems which combines Computer-Assisted Software Engineering (CASE) tools and techniques, user-driven prototyping, and stringent project delivery time limits into a potent, tested, reliable formula for top-limits into a potent, tested, reliable formula for top-notch quality and productivity. RAD drastically raisesthe quality of finished systems while reducing the time it takes to build them”

Professor Clifford Kettemborough of Whitehead College, University of

Redlands

ContCont……

• Reduces system development time (fast)

• Gives quality result

• Takes the advantage of powerful development software that has evolved recentlysoftware that has evolved recently

• saving valuable resources.

• With such conventional methods, there is a long delay before the customer gets to see any results and the development process can take so long that the customer’s business could fundamentally change before the system is even ready for usebefore the system is even ready for use

• RAD compresses the step-by-step development

of conventional methods into an iterative process.

• The RAD approach thus includes

– developing and refining the data models, process models, and prototype in parallel using an iterative process. iterative process.

– User requirements are refined, a solution is designed, the solution is prototyped, the prototype is reviewed, user input is provided, and the process begins again.

Aspects of RADAspects of RAD

• methodology,

• people,

• management,

• tool

Approach to RAD by McConnellApproach to RAD by McConnell

• Successful RAD approach

– Avoid classic mistakes

– Applying development fundamentals

– Managing risks to avoid terrible delays– Managing risks to avoid terrible delays

– Applying schedule oriented practice

Ten of McConnell’s 36 Classic Development Ten of McConnell’s 36 Classic Development MistakesMistakes

• Refer page 302

Advantages and Disadvantage of RADAdvantages and Disadvantage of RAD

• Advantages:

– Save time, money and human resource

– Fit between user requirements and system specificationspecification

– Ability to rapidly change system design as demanded by user

– System optimization

– System element from user viewpoint

Advantages and Disadvantage of RADAdvantages and Disadvantage of RAD

• Disadvantages– Speed and low cost may lead to low system

quality

– Danger of misalignments of system developed via RAD with the business due to missing information RAD with the business due to missing information on underlying business process

– May have inconsistent internal design within and across systems

– Insufficient documentation and violation of cording standards

ContCont……

– Difficulties with module reuse for future systems

– Lack of scalability

– Lack of attention to later systems administration built into the systembuilt into the system

– High costs of commitment on the part of key user personnel

Lesson 19

ComponentComponent--Based Software Based Software ComponentComponent--Based Software Based Software EngineeringEngineering

W.C.UduwelaDepartment of Mathematics and Computer

Science

ComponentComponent--based developmentbased development

• Component-based software engineering (CBSE) is an approach to software development that relies on software reuse.

• Components are more abstract than object classes and can be considered to be stand-alone service providers.

CBSE essentialsCBSE essentials

• Independent components specified by their interfaces.

• Component standards to facilitate component integration.integration.

• Middleware that provides support for component inter-operability.

• A development process that is geared to reuse.

CBSE and design principlesCBSE and design principles

• Apart from the benefits of reuse, CBSE is based on sound software engineering design principles:– Components are independent so do not interfere

with each other;Components are independent so do not interfere with each other;

– Component implementations are hidden;

– Communication is through well-defined interfaces;

– Component platforms are shared and reduce development costs.

CBSE problemsCBSE problems

• Component trustworthiness - how can a component with no available source code be trusted?

• Component certification - who will certify the quality of components?

• Emergent property prediction - how can the • Emergent property prediction - how can the emergent properties of component compositions be predicted?

• Requirements trade-offs - how do we do trade-off analysis between the features of one component and another?

Component definitionsComponent definitions

• Councill and Heinmann:

– A software component is a software element that conforms to a component model and can be independently deployed and composed without modification according to a composition standard.a composition standard.

• Szyperski:

– A software component is a unit of composition with contractually specified interfaces and explicit context dependencies only. A software component can be deployed independently and is subject to composition by third-parties.

ComponentsComponents

• Components provide a service without regard to where the component is executing or its programming language– A component is an independent executable

entity that can be made up of one or more A component is an independent executable entity that can be made up of one or more executable objects;

– The component interface is published and all interactions are through the published interface;

Component as a service providerComponent as a service provider

• The component is an independent, executable entity. It does not have to be compiled before it is used with other components.

• The services offered by a component are • The services offered by a component are made available through an interface and all component interactions take place through that interface.

Component characteristics 1Component characteristics 1

Standardised Component standardisation means that a component that isused in a CBSE process has to conform to some standardisedcomponent model. This model may define componentinterfaces, component meta-data, documentation, compositionand deployment.

Independen t A component should be independen t Š it should be possible toIndependen t A component should be independen t Š it should be possible tocompose and deploy it without having to use other specificcomponents. In situations where the component needsexternally provided services, these should be explicitly set outin a ŌrequiresÕ interface specification.

Composable For a component to be composable, all external interactionsmust take place through publicly defined interfaces. Inaddition, it must provide external access to information aboutitself such as its methods and attributes.

Component characteristics 2Component characteristics 2

Deployable To be deployable, a component has to be se lf-contained andmust be able to operate as a stand-alone entity on somecomponent platform that implements the component model.This usually means that the component is a binary componentThis usually means that the component is a binary componentthat does not have to be compiled before it is deployed.

Documented Components have to be fully documented so that potentialusers of the component can decide whether or not they meettheir needs. The syntax and, ideally, the semantics of allcomponent interfaces have to be specified.

Component interfacesComponent interfaces

• Provides interface

– Defines the services that are provided by the component to other components.

• Requires interface• Requires interface

– Defines the services that specifies what services must be made available for the component to execute as specified.

Component interfacesComponent interfaces

Provides int erfaceRequires int erface

Defines the services Defines the servicesthat are providedComponentfrom the component’s

environment that it

uses

that are providedby the componentto other components

Components and objectsComponents and objects

• Components are deployable entities.

• Components do not define types.

• Component implementations are opaque.

• Components are language-independent.• Components are language-independent.

• Components are standardized.

The CBSE processThe CBSE process

• When reusing components, it is essential to make trade-offs between ideal requirements and the services actually provided by available components.

• This involves:• This involves:– Developing outline requirements;

– Searching for components then modifying requirements according to available functionality.

– Searching again to find if there are better components that meet the revised requirements.

The CBSE processThe CBSE process

Identify candidate

components

Outline

system

requir ements

Modify

requir ements

according to discovered

components

Identify candidate

components

Architectur al

design

Compose

components to

create system

The component identification processThe component identification process

ComponentComponent ComponentComponentselection

Componentsearch

Componentvalidation

Component identification issuesComponent identification issues

• Trust. You need to be able to trust the supplier of a component. At best, an untrusted component may not operate as advertised; at worst, it can breach your security.

• Requirements. Different groups of components will • Requirements. Different groups of components will satisfy different requirements.

• Validation. – The component specification may not be detailed enough

to allow comprehensive tests to be developed.

– Components may have unwanted functionality. How can you test this will not interfere with your application?

ArianeAriane launcher failurelauncher failure

• In 1996, the 1st test flight of the Ariane 5 rocket ended in disaster when the launcher went out of control 37 seconds after take off.

• The problem was due to a reused component from a previous version of the launcher (the Inertial previous version of the launcher (the Inertial Navigation System) that failed because assumptions made when that component was developed did not hold for Ariane 5.

• The functionality that failed in this component was not required in Ariane 5.

Component compositionComponent composition

• The process of assembling components to create a system.

• Composition involves integrating components with each other and with the component with each other and with the component infrastructure.

• Normally you have to write ‘glue code’ to integrate components.

Types of compositionTypes of composition

• Sequential composition where the composed components are executed in sequence. This involves composing the provides interfaces of each component.

• Hierarchical composition where one component calls • Hierarchical composition where one component calls on the services of another. The provides interface of one component is composed with the requires interface of another.

• Additive composition where the interfaces of two components are put together to create a new component.

Types of compositionTypes of composition

A A

(a)

B B

A B

(b) (c)

Interface incompatibilityInterface incompatibility

• Parameter incompatibility where operations have the same name but are of different types.

• Operation incompatibility where the names of • Operation incompatibility where the names of operations in the composed interfaces are different.

• Operation incompleteness where the provides interface of one component is a subset of the requires interface of another.

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Thank You!Thank You!Thank You!Thank You!