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9/3/09 15:07 EEC 521: Software Engineering 1

EEC 521: Software Engineering

The Software ProcessPrescriptive Process Models


The Top Thrill Dragster• 420 ft tall• Max speed over 120

mph• World’s second

fastest roller coaster


Roller Coaster Process• The park conceptualizes what it wants• Hires a company to build it; communicates its concept to

the builder• Builder plans the coaster, and communicates its plans and

the budget to park for approval• Builder then makes models of the coaster and makes sure

that all the requirements are met• The models also help understand the physics a little

better than plain calculations• The actual coaster is built, and tested• The coaster is delivered to the park and is opened to

public

Concept

Communication

Planning

Modeling

Construction

Deployment


What is a Software Process?• A series of predictable steps that helps

produce a timely, high-quality result• What are the actual steps?

• Di!ers from one process model to another

• Important because it provides stability,control and organization

“A process de"nes who is doing what, when, and how to reach acertain goal” – Ivar Jacobson, Grady Booch, and James Rumbaugh


Software Engineering:A Layered Technology

A quality focus

Process

Methods

Tools

It shoulddo X.

It shoulddo Y.

I’m notsure…

Software Engineering

Software requirements are embodiedknowledge that is initially dispersed, tacit,

latent, and incomplete.

Software engineering encompasses aprocess, management and technical

methods, and tools.


Generic Software EngineeringPhases

• The de"nition phase• What product is going to be built?

• The development phase• How will the product be built, and how will it be

tested?• The support phase

• Incorporate changes from the four sources ofchange.• Correction• Adaptation• Enhancement• Prevention


Process Framework• Provides the foundation for a complete

software process• Identi"es framework activities

• Applicable to all software projects• De"nes a set of software engineering actions• Each action has a set of work tasks

• De"nes umbrella activities• Applicable to the process across all process stages• Focus is on project management, tracking, and control


Generic Framework Activities• Communication

– Communication/collaboration with customer• Planning

– Technical tasks, risks, resource requirements,schedule, etc.

• Modeling– Design, models, prototypes, customer feedback

• Construction– Coding, testing

• Deployment– Delivery


Umbrella Activities• Software project tracking and control• Risk management• Software quality assurance• Formal technical reviews• Measurement• Software con"guration management• Reusability management• Work product preparation and production


Process Variety• Prescriptive models

–Waterfall model–Spiral model–The Uni"ed Process–Formal methods

• In general, moredisciplined, and morerules

• Agile models– Extreme

programming– Adaptive software

development– Scrum– Feature-driven

Development

• Fewer rules, focus onend product


SEI CMMI• Level 0: Incomplete

• No process• Level 1: Performed

• Speci"c goals of process area are performed• Level 2: Managed

• Work in process area conforms to a de"ned policy• Level 3: De"ned

• The process is tailored to the speci"c organization• Level 4: Quantitatively Managed

• Quantitative objectives are established and reviewed• Level 5: Optimized

• Process is adapted and optimized based on statisticalevidence


Process Patterns• A consistent template for describing

important characteristics for the softwareprocess

• Provides suggested solutions to recurringproblems in the software process e.g.,customer-communication, project-teamassembly

• Can be reused in several di!erent contexts


General Characteristics ofPrescriptive Models• Framework activities populated with

explicit tasks for software engineeringactions

• The models prescribe how the variousactions are to be executed

• The models prescribe a work!ow


The Waterfall Model

• Sequential approach to softwaredevelopment

CommunicationProject initiationRequirements Planning

EstimationSchedulingTracking

ModelingAnalysisDesign Construction

CodeTest Deployment

DeliverySupportFeedback


The Waterfall Model (2)Good for projects that can be planned completely rightat the beginning

– Well-de"ned requirements– No changes anticipated

Most real projects cannot be built sequentiallyMost new projects have inherent uncertaintyNo way of checking if requirements are met


The Incremental Model

• Iterative application of the Waterfall• Product is “grown” through several

increments

CommunicationProject initiationRequirements

PlanningEstimationSchedulingTracking Modeling

AnalysisDesign

ConstructionCodeTest

DeploymentDeliverySupportFeedbackSo

ftwar

e fu

nctio

nalit

y

Project time



AnalysisDesign


DeploymentDeliverySupportFeedback



AnalysisDesign


DeploymentDeliverySupportFeedback

Release 1

Release 2

Release 3


The Incremental Model(2)• The model is an evolutionary approach

– The product gains more features with everyiteration

• Similar to Waterfall– Each increment is built sequentially– Changes are expensive inside an increment

• Each increment is a usable, "nishedproduct– Not a prototype


Prototyping• Requirements are very fuzzy

– Idea is there, but no details– Customer is not able to clearly state requirement

• Communication is key

Communication Quick plan

Modeling and Quick Design

Prototypeconstruction

Deployment, Delivery &Feedback


Prototyping (2)

Great way to elicit requirements– Can serve as requirements gathering

technique for other process models– Saves a lot of change later on in the life-cycle

Customer may not like the “throw-away”nature of the prototype

May want to shorten schedule

Bad development choices may be made


The Spiral Model

• The most mature of evolutionary models– Controlled and systematic, yet evolutionary

• Risk-driven process model– Cyclic approach

• Increase degree of de"nition and implementation• Decrease degree of risk

– Anchor point milestones


The Spiral Model (2)PlanningEstimationSchedulingRisk analysis

ModelingAnalysisDesign


DeploymentDeliveryFeedback

Communication

Start


The Spiral Model (3)

Realistic model for large projectsPeriodic risk evaluation leads to betterutilization of resourcesWhen is the project !nished?Considerable risk assessment expertise isrequired


The Uni"ed Process

• Uni"es important features of other processmodels

• Speci"cally targeted at Object-Orientedsystem development

• Based on the concept of use-cases• Includes a set of design tools

– Uni"ed Modeling Language


The Uni"ed Process (2)

Communication

Planning

Modeling

Construction

Deployment

Software incrementRelease

Inception

ElaborationConstruction

Transition

Production


The Uni"ed Process (3)• De"ned set of work products

– Use-case model (inception)– Non-functional requirements (elaboration)– Analysis model (elaboration)– Design model (construction)– Implementation model (construction)– Test cases (construction)– Beta test reports (transition)– User feedback reports (transition)


Other PrescriptiveModels• Component-Based Development

– Integrating components with well-de"nedinterfaces to build system

• Formal Methods Model– Speci"cation, development, and veri"cation

of system using rigorous mathematicalnotation


Reading AssignmentGilda Pour, Martin L. Griss, and Michael Lutz.The Push to Make Software EngineeringRespectable. IEEE Computer. May 2000. pages35 – 43.

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