Introduction to Software Development (Software Engineering - I) Course Instructor: Kashif Ihsan...

Introduction to Introduction to Software DevelopmentSoftware Development(Software Engineering - I)(Software Engineering - I)

Course Instructor:

Kashif Ihsan

1Kashif Ihsan, Lecturer CS, MIHE

Chapter # 03Chapter # 03Process ModelsProcess Models

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Table of Contents: Introduction Linear Sequential Model System Development Life Cycle (SDLC) Prototyping Model

Throw Away Prototype Evolutionary Prototype

Rapid Application Development Model Evolutionary Software Model

The Incremental Model The Spiral Model

Software Development Software Development ProcessProcessSoftware development process is a

coherent (logically, orderly) set of activities for specifying, designing, implementing and testing software systems.

A software process model is an abstract (theoritical) representation of a process. It presents a description of a process from some particular perspective.

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Software Development Software Development ProcessProcessA software development process

model defines software development phases, their sequence, tools and methods to be used, while trying to maximize quality of software and minimize resource usage such as money and time and man-power.

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Software Process ModelSoftware Process ModelThe software process model maybe

defined as a simplified description of a software process, presented from a particular perspective.

Examples of process perspectives are◦ Work-flow perspective◦ Data-flow perspective◦ Role perspective

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Work-Flow PerspectiveWork-Flow PerspectiveThe work-flow model shows the

sequence of activities in the process along with their inputs, outputs and dependencies.

The activities in the model represent human actions.

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Data-Flow PerspectiveData-Flow PerspectiveThe data-flow model

represents the process as a set of activities, each of which carries out some data transformation.

It shows how the input provided to the process is transformed to an output.

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Role PerspectiveRole PerspectiveThe role perspective

represents the roles of people involved in the software process and the activities for which they are responsible.

It represents who does what.

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Linear Sequential Model Linear Sequential Model (LSM)(LSM)It is also called Waterfall Model.

This model suggests a systematic sequential approach to software development.

Linear sequential model starts at the system level and go through analysis, design, coding and testing.

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Linear Sequential ModelLinear Sequential Model

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Analysis

design

coding

testing

implementation

Requirementgathering

Advantages of LSMAdvantages of LSMThe oldest and mostly used model.

Formal review at the end of each phase allows maximum management control.

It provide a template into which method for analysis, design, coding and testing can be placed.

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Disadvantages of LSMDisadvantages of LSMThe end-user does not see the solution

until the system is nearly complete.

Users get a system that meets the need as understood by the developers; this may not be what was really needed.

Often, users’ needs go unstated or are misunderstood.

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Disadvantages of LSMDisadvantages of LSMUsers cannot easily review

intermediate products and evaluate whether a particular product meets their business requirements.

The activities can not be reversed back at any stage.

It is time consuming.

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System Development Life System Development Life CycleCycleSDLC use the linear sequential approach toward the development of s/w. The only change that makes SDLC different from LSM is that the activities can be reversed back at any stage.

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Requirementgathering

Analysis

design

coding

testing

implementation

System Development Life System Development Life CycleCycle

Prototyping ModelPrototyping ModelOne of the major disadvantage of

Linear Sequential Model was that the customer can not tell all the requirements at the start.

So, in order to get all the requirements from the user efficiently, prototyping model was introduced.

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PrototypePrototypeBefore designing the actual

product, a rough sketch (driving s/w) is drawn which is known as prototype.

Prototype means an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.

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Stages of PrototypingStages of Prototyping

Prototyping model consist of three stages: Listen to the customer Build & revise stage Customer test stage

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Stages of PrototypingStages of Prototyping

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Prototyping ModelPrototyping Model

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Requirementgathering

analysis design coding testing

Types of PrototypingTypes of Prototyping

Basically there are two types of prototyping:

Throw Away Prototype

Evolutionary Prototype

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Throw Away PrototypeThrow Away PrototypeThis approach is also called

Closed Ended Approach.

This approach suggests that the constructed prototype should be discarded and the software should be build from the scratch.

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Throw Away PrototypeThrow Away PrototypeThe objective of throw-away

prototyping is to validate or derive the system requirements. The prototyping process starts with those requirements which are poorly understood.

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Evolutionary PrototypeEvolutionary PrototypeThis is also called Open Ended

Approach.In this approach, the prototype

constructed will be finally converted into the final product.

The main goal when using Evolutionary Prototyping is to build a very robust prototype in a structured manner and constantly refine it.

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Evolutionary PrototypeEvolutionary PrototypeThe objective of evolutionary

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

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Evolutionary PrototypingEvolutionary Prototyping

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Build prototypesystem

Develop abstractspecification

Use prototypesystem

Deliversystem

Systemadequate?

YES

N

Advantages of PrototypingAdvantages of PrototypingEarly visibility of the prototype gives

users an idea of what the final system looks like.

Encourages active participation among end users and the developer/producer.

Helps to deliver the product in the best possible quality.

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Disadvantages of Disadvantages of PrototypingPrototyping

As the prototype is given to the customer, the customer may realize that this is the final product.

Structure of system can be damaged since many changes could be made.

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Disadvantages of Disadvantages of PrototypingPrototyping

It is not suitable for very large applications /softwares.

It may slow the development process, if there are large number of end users to satisfy.

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RAD ModelRAD ModelRAD stands for “Rapid Application

Development”.It is an incremental software

development model with very short time period (development cycle).

In this model, the software engineer use the linear sequential approach using component based construction.

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RAD ModelRAD ModelThe development process starts with

the development of preliminary data models and business process models.

In the next stage, requirements are verified using prototyping, eventually to refine the data and process models. These stages are repeated iteratively.

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RAD Model

RAD ModelRAD ModelBusiness Modeling: 

The information flow among business functions is defined by answering questions like what information drives the business process, what information is generated, who generates it, where does the information go, who process it and so on.

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RAD ModelRAD ModelData Modeling: 

The information collected from business modeling is refined into a set of data objects (entities) that are needed to support the business. The attributes (character of each entity) are identified and the relation between these data objects (entities) is defined.

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RAD ModelRAD ModelProcess Modeling: 

The data objects defined in the data modeling phase are transformed to achieve the information flow necessary to implement a business function. Processing descriptions are created for adding, modifying, deleting or retrieving a data object.

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RAD ModelRAD ModelApplication Generation:

Automated tools are used to facilitate construction of the software.

Testing:Many of the programming components have already been tested since RAD emphasizes re-use. This reduces overall testing time. But new components must be tested and all interfaces must be fully exercised.

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Advantages of RAD ModelAdvantages of RAD Model

It use already existent components.

Development life cycle is very short.

Testing is reduced.

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Disadvantages of RAD Disadvantages of RAD ModelModel

For large system, RAD model requires sufficient human resources.

The customer and developer should be active, because the laziness of any one may lead to failure.

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Evolutionary Software Evolutionary Software ModelModelEvolutionary software model is

the combination of Linear Sequential Model and the Prototyping.

There are two main types of Evolutionary Software Models:i. The Incremental Model

ii. The Spiral Model

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Incremental ModelIncremental ModelIncremental model use the linear

sequential approach with the iterative nature of prototyping.

Incremental model delivers the software in small but usable pieces called the “increment”.

First increment is called the core product in which the basic requirement are fulfilled.

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Incremental ModelIncremental ModelThe core product than act as

input for further increments.

More specifically, the model is designed, implemented and tested as a series of incremental builds until the product is finished.

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Incremental ModelIncremental Model

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Validateincrement

Build systemincrement

Specify systemincrement

Design systemarchitecture

Define systemdeliverables

Systemcomplete?

Integrateincrement

Validatesystem

Deliver finalsystem

YES

NO

Advantages of Incremental Advantages of Incremental ModelModelIt is well suited in the case where

the staffing is unavailable at the start.

Each iteration delivers a functionally operational product and thus customers can get to see the working version of the product at each stage.

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Users may experiment with delivered increments while others are being developed. therefore, these serve as a form of prototype system.

The main DISADVANTAGE is that it is too time consuming.

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Advantages of Incremental Advantages of Incremental ModelModel

Spiral ModelSpiral ModelThe Spiral Model is an evolutionary

software process model that couples the iterative nature of prototyping with the controlled and systematic aspects of the Linear Sequential Model.

Using the Spiral Model. the software is developed in a series of incremental releases.

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Spiral ModelSpiral ModelUnlike the Iteration Model, where

in the first product is a core product, in the Spiral Model the early iterations could result in a paper model or a prototype.

However, during later iterations, more complex functionalities could be added.

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Spiral ModelSpiral Model

A Spiral Model is divided into a number of framework activities, also called task regions. These task regions could vary from 3-6 in number and they are:

Customer Communication - tasks required to establish effective communication between the developer and customer.

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Spiral ModelSpiral ModelPlanning - tasks required to define

resources, timelines and other project related information /items.

Risk Analysis - tasks required to assess the technical and management risks.

Engineering - tasks required to build one or more representation of the application. Kashif Ihsan, Lecturer CS, MIHE 48

Spiral ModelSpiral ModelConstruction & Release - tasks

required to construct, test and support (e.g. Documentation and training)

Customer evaluation - tasks required to obtain periodic customer feedback so that there are no last minute surprises.

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Advantages of Spiral Advantages of Spiral ModelModelIt is a realistic approach to the

development because the software evolves as the process progresses. In addition, the developer and the client better understand and react to risks at each evolutionary level.

The model uses prototyping as a risk reduction mechanism and allows for the development of prototypes at any stage of the evolutionary development.

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Advantages of Spiral Advantages of Spiral ModelModelIt maintains a systematic

stepwise approach, like the classic waterfall model, and also incorporates into it an iterative framework that more reflect the real world.

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Disadvantages of Spiral Disadvantages of Spiral ModelModelIf in first stages the risk are not

managed then it will create problem.

It has not been employed as much proven models and hence may prove difficult to ‘sell’ to the client.

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The End

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