processmodels1

8/7/2019 processmodels1

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Process Models


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Software Process

Process consists of activities/steps to becarried out in a particular order

Software process deals with both technicaland management issues

Consists of different types of process

Process for software development: produces

software as end-result multiple such processes may exist

a project follows a particular process


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Characteristics of a Good Process

Should be precisely defined no ambiguity aboutwhat is to be done, when, how, etc.

It must be predictable-Predictable with respect to

effort, cost Facilitates early detection of and removal of

defects

It should facilitate monitoring and improvement


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PRESCRIPTIVE PROCESSMODELS

A prescriptive model prescribes how a new software system should

be developed.

Prescriptive models are used as guidelines or frameworks to

organize and structure how software development activitiesshould be performed, and in what order.

Describe a set of process elements-activities,engineering

actions,tasks,work products,quality assurance,change controlmechanisms.


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PRESCRIPTIVE PROCESSMODELS

Water fall model

Incremental process model

Incremental model

RAD model

Evolutionary process models

Prototyping Spiral model

Concurrent development model

Agile process models


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The first model proposed was the waterfall

model [Royce 1970]

Water fall Model


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A series of steps where each steps falls

to the next step. One phase has to be complete before moving

onto the next phase.

Separate and distinct phases of specification and

development.


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drawbacks

1.The main drawback of the waterfall model is the difficulty of

acommodating change after the process is underway.difficult

to correct the previous stages

2. Inflexible partitioning of the project into distinct stages makesit difficult to respond to changing customer requirements.

3. Therefore, this model is only appropriate when the

requirements are well-understood and changes will be fairly

limited during the design process.

4.A working version will be available only late in the project time

span.

The waterfall model is mostly used for large systems engineering projects

where a system is developed at several sites.


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Incremental process model

Rather than deliver the system as a single delivery, the

development and delivery is broken down into increments

with each increment delivering part of the required

functionality.

User requirements are prioritised and the highest priority

requirements are included in early increments.

Once the development of an increment is started, the

requirements are frozen though requirements for later

increments can continue to evolve.


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1.Incremental model


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1.Incremental model

First step gets a quick version that doespart of project.

Second increment gets a better, moredetailed version.

Successive increments get better andmore complete software.


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1.Incremental model

The incremental model combines elements of the waterfall

model applied in iterative fashion.

It also applies linear sequence in a staggered fashion as

calendar time progress. Each linear sequence produces deliverable increments of the

software.

First incremental is core product featuring the basic

requirements .

Core products is used by customer ,evaluated and a modified

plan for the next increment is given

Ex: word processing.(i, increment, ii, increment, iii, increment


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2.RAD model


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Traditional vs RAD


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2.RAD Model

RAD is an incremental software process model

that emphasizes a short development cycle.

It is a high speed adaptation of the water fallmodel.

It process enables a development team to

create a fully functional system within a very

short time period.

Its goals are: faster, better, cheaper


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2.RAD Model

The RAD model follows a component based approach.

Separate the project to modules

In this approach individual components developed by different

people are assembled to develop a large software system.

Put together a team of Smart Guys from multiple disciplines

Show it to the U

SERS

Get Feedback

Incorporate for the final product

It encourages the development of program component

reusable.


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Drawbacks

criticized because it lacks a methodology and a

designed architecture

flexibility of RAD systems decreases as applications

grow

RAD tends to fail when

Application must interoperate with existing programs

Performance and reliability are critical

The system cannot be modularized

New technologies are used


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Evolutionary process model


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Evolutionary process model

It is also iterative, they are characterized in a

manner that enables software engineers to

develop increasingly more complete versions

of the software.

Core product with requirement specification is

defined but details of the product has to be

yet defined

Product will evolves over time


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1.PROTOTYPING

Co m m u n ic a t io n

Q u ic k p l a n

Co n st r u ct io no f

p r o t o t y p e

M o d e li n g

Q u ic k d e s ig n

D e liv e r y

& F e e d b a c k

D e p l o y m e n t


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1.PROTOTYPING

In this model the developer and client interact to establishedthe requirements of the software.

Define the broad set of objectives.

This is follow up by the quick design, in which the visibleelements of the software, the input and the output aredesigned.

The quick design stresses the clients view of the software .

The final product of the design is a prototype.

The client the evaluates the prototype and provides itsrecommendations and suggestion to the analyst.

The process continues in an iterative manner until the all theuser requirements are met.


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1.PROTOTYPING

Drawbacks:

Customers like the prototype and want to

place it in production. Developers forget the design decisions and

their mistakes leak into the prototype which

they have developed quickly.

Documentation may get neglected

Effort in building a prototype may be wasted

Difficult to plan and manage


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2.Spiral Model

The spiral model developed by Boehm combines thephilosophy ofINM,RAD and LSM models with the use of

prototyping.

The spiral model is recommended where the requirements and

solution call for developing full-fledge , large, complicatedsystem with lots of features and facilities from the scratch.

It is used when experimenting on technology , trying out new

skills and when the user is not able to offer requirements in

clear terms.

It emphasis at the quick development of the software, which is

released in increments.


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2.Spiral Model

commu ication

planning

modeling

constructiondeployment

delivery

feedback

start

analysis

design

code

test

estimation

scheduling

risk analysis


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2.Spiral Model

The process is represented as a spiral, each loop in the

spiral representing a process phase

Five sectors per loop: communication, risk assessment and

reduction, development and validation, planning At each cycle through the spiral, milestones are achieved

and risk is reevaluated.

Risk is explicitly taken into consideration which helps to

reduce technical risk. This model is more in tune with large real-life project development.

It is suitable for application that can be use an object oriented approach

to develop software.


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2.Spiral Model-disadvantages

The spiral model has the following disadvantages:

It can cause problems in negotiating a development

contract with the client.

It requires considerable experience in risk

management for the project to be successful.

It requires a lot of patience and time in years before

this models effectiveness can be assessed accurately.


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U n d e rre v i e w

B a s e l i n e d

D o n e

U n d e r

re v i s i o n

A w a i t i n g

c h a n g e s

U n d e r

d e v e l o p m e n t

n o n e

M o d e l i n g a ct i v i t y

re p re s e n t s t h e st a t e

o f a s o ft w a re e n gi n e e r i n g

a c t i v i t y ort a s k

3.Concurrent development model

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