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Software Process

Week 3 Lecture 6

Instructors name: Saliha Zahoor

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The incremental

The core product is used by the customers and

as a result of use a plan is developed for the

next increment.

The incremental process model like

prototyping and other evolutionary is iterative

in nature.

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The Incremental Model

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Incremental Model

Functionality produced and delivered in small increments

Focus attention first on essential features and add functionality only if and

when needed

May be hard to add features later

Variant: Incremental implementation only Follow waterfall down to implementation

During requirements analysis and system design

Define useful subsets that can be delivered

Define interfaces that allow adding later smoothly

Different parts implemented, tested, and delivered according to differentpriorities and at different times.

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The incremental model

This is a combination of the linear sequentialmodel and the iterative model.

The problem is broken into increments, and eachincrement is tackled as a linear sequence.

Further increments can either be done after theprevious ones, or can overlap with the previousones.

Incremental delivery focuses on the delivery of anoperational product with each increment.

Early increments are stripped-down versions ofthe final product.

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Incremental model advantages

Less staffing is required than in a RAD project

Early delivery is guaranteed

Progress of the whole project is not delayed if one of theresources is not available for part of it

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The RAD Model

Rapid Application Development(RAD) is an incremental

software development process model that emphasizes an

extremely short development cycle.

The RAD model is a high speed adaptation of the linear

sequential model in which rapid development is achieved by

using component based construction.

If requirements are well understood and project scope is

constrained the RAD Process enables the team to create a

fully functional system within very short time periods e.g 60to 90 days.

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The RAD Model

A component-based construction approach isused.

To use this approach, the project scope must be

constrained and the requirements should be wellunderstood.

A task that should take no more than ninety daysto complete is modelled, generated and

implemented. There can be several teams working on different

components during this ninety day time-box.

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Iterative Models-RAD

RAD

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The RAD Model Phases

Communication

Modeling

Business Modeling

Data Modeling

Process Modeling

Construction

Application Generation

Testing and Turnover

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RAD Model Phases

Business Modeling: What information drives thebusiness process? What information isgenerated? Who generate it? Where does theinformation go? Who processes it?

Data Modeling: The information flow as part ofthe business modeling phase is refined into set ofdata objects that are needed to support the

business. The characteristics of each object areidentified and the relationship between theseobjects defined.

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The RAD Model Phases

Process Modeling: Process descriptions are created foradding ,modifying , deleting or retrieving a data object.

Application Generation: The RAD process works toreuse existing program components or create reusable

components. Emphasizes the use of preexistingsoftware components and the application of automaticcode generation.

Testing and turnover: Since RAD process emphasisreuse, many of the program components have already

been tested. This reduces overall testing time. Howevernew components must be tested and all interfacesmust be fully exercised.

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The RAD model

90

days

Team 1

Testing &

Turnover

Application

Generation

Business

modelling

Data

modelling

Process

modelling

Team 2

Testing &

Turnover

Application

Generation

Business

modelling

Data

modelling

Process

modelling

Team 3

Testing &

Turnover

Application

Generation

Business

modelling

Data

modelling

Process

modelling

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Problems with RAD

For large, scalable projects, RAD requires sufficient human

resources to create the right number of RAD teams

RAD requires developers and customers who are committed

to the rapid-fire activities necessary to complete a system in

this time frame, or failure will result.

RAD is not suitable for many project types.

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Spiral development

Process is represented as a spiral rather thanas a sequence of activities with backtracking

Each loop in the spiral represents a phase in

the process. No fixed phases such as specification or

design - loops in the spiral are chosen

depending on what is required Risks are explicitly assessed and resolved

throughout the process

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The spiral model

It explicitly embraces prototyping and an iterativeapproach to software development.Start by developing a small prototype.

Followed by a mini-waterfall process, primarily to gather

requirements.Then, the first prototype is reviewed.

In subsequent loops, the project team performs furtherrequirements, design, implementation and review.

The first thing to do before embarking on each new loopis risk analysis.

Maintenance is simply a type of on-going development.

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Spiral Model

Precede each phaseby

Alternatives

Risk analysis

Follow each phaseby

Evaluation

Planning of nextphase

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Spiral model detailsSpiral model is divided into a number of framework activities, named as task regions.3-6

task regions. Each task region has its own task sets.

Customer

communication

Construction and release

Engineering

Risk analysis

Planning

Customer

evaluation

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Process iteration

Modern development processes take iteration asfundamental, and try to provide ways ofmanaging, rather than ignoring, the risk

System requirements ALWAYS evolve in thecourse of a project so process iteration whereearlier stages are reworked is always part of theprocess for large systems

Iteration can be applied to any of the genericprocess models

Two (related) approaches Incremental development

Spiral development

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Component Based Development

Object oriented technologies provide the technicalframework for a component based process model forsoftware engineering.

This incorporates many of the characteristics of the spiral

model. It is evolutionary in nature, demanding an iterative approach

to the creation of software.

However, it composes applications from pre-packagedsoftware components.

The construction & release activity in Boehms model isreplaced by an Engineering construction and releaseactivity.

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ComponentBased

Development

Identify

candidate

components

Construct

nth

iteration of

system

Put new

component

s in library

Look up

component

s in library

Extract

component

s if available

Build

components

if unavailable

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The Formal Method Model

Encompasses a set of activities that leads to

formal mathematical specification of computer

software

Specify, develop and verify a computer based

system by applying a rigorous mathematical

notation.

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Advantages

Mechanism for eliminating ambiguity,

incompleteness, and inconsistency

Formal methods provide mathematical

analysis for ensuring correct analysis and

design

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Disadvantages

Quiet expensive and time consuming

Extensive Training required

Difficult to communicate for technically

unsophisticated customer

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Methods and tools

There are many methodologies and tools that are available.

The methodology should fit a particular process model that issuited to the task being undertaken, and the tool or set oftools should provide automated force at related parts of the

life cycle.The methodology should include diagrammatic techniques,such

as SSADM for linear sequential systems or Rational UnifiedProcess (RUP) for object-oriented systems.