Software Engineering

Saeed Akhtar

The University of Lahore

Lecture 3Originally shared for:

mashhoood.webs.com

Review of Last LectureWhat is a software process?

What are the activities of a software process?

Software specification consist of ?

Testing Stages are?

Characteristics of a Good Process are?

Objectives

To introduce software Process Models and types of SDLC

To set out the answers to key questions about software Process Models

Software Process Model

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

Waterfall modelRequirements

definition

System andsoftware design

Implementationand unit testing

Integration andsystem testing

Operation andmaintenance

Waterfall model phases

Requirements analysis and definition

System and software design

Implementation and unit testing

Integration and system testing

Operation and maintenance

Advantages of Waterfall Model

Staged development cycle enforces discipline

Every phase has a defined start and end point

Minimal wastage of time and resources

Drawbacks of Waterfall ModelThe main drawback of the waterfall model is

the difficulty of accommodating change after the process is underway. One phase has to be complete before moving onto the next phase.

Inflexible partitioning of the project into distinct stages makes it difficult to respond to changing customer requirements.

Therefore, this model is only appropriate when the requirements are well-understood and changes will be fairly limited during the design process.

Drawbacks Cont’dFew business systems have stable

requirements.

The waterfall model is mostly used for large systems engineering projects where a system is developed at several sites.

customer must have patience, not fast enough for delivery of modern internet based software

Component-based software engineeringBased on systematic reuse where systems are

integrated from existing components or COTS (Commercial-off-the-shelf) systems.

CBSE Process stages

Component analysis

Requirements modification

System design with reuse

Development and integration

Reuse-oriented development

Requirementsspecification

Componentanalysis

Developmentand integration

System designwith reuse

Requirementsmodification

Systemvalidation

CBSE Advantages

Management of Complexity

Reduce Development Time

Increased Productivity

Improved Quality

Less Expensive

Disadvantages of CBSEDevelopment of Components

Lack of Components

Component Maintenance Costs

Reliability and Sensitivity to changes

Unsatisfied Requirements

Incremental ModelRather 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.

Incremental Model

Validateincrement

Develop systemincrement

Design systemarchitecture

Integrateincrement

Validatesystem

Define outline requirements

Assign requirements to increments

System incomplete

Finalsystem

Incremental development advantagesCustomer value can be delivered with each

increment so system functionality is available earlier.

Early increments act as a prototype to help elicit requirements for later increments.

Lower risk of overall project failure.

The highest priority system services tend to receive the most testing.

Incremental development disadvantagesEach phase of an iteration is rigid and do not overlap

each other

Common software facilities may be difficult to identify

Mapping requirements to increments may be not easy

Problems may arise pertaining to system architecture because not all requirements are gathered up front for the entire software life cycle

Thank You