Software Engineering

Course Instructor: Aisha Azeem

Types of Software Applications System software: such as compilers, editors, file

management utilities

Application software: stand-alone programs for specific needs.

Engineering/scientific software: Characterized by “number crunching”algorithms. such as automotive stress analysis, molecular biology, orbital dynamics etc

Embedded software resides within a product or system. (key pad control of a microwave oven, digital function of dashboard display in a car)

Product-line software focus on a limited marketplace to address mass consumer market. (word processing, graphics, database management)

WebApps (Web applications) network centric software. As web 2.0 emerges, more sophisticated computing environments is supported integrated with remote database and business applications.

AI software uses non-numerical algorithm to solve complex problem. Robotics, expert system, pattern recognition game playing

Types of Software Applications

FAQ about software engineeringQuestion Answer

What is software? Computer programs, data structures and associated documentation. Software products may be developed for a particular customer or may be developed for a general market.

What are the attributes of good software?

Good software should deliver the required functionality and performance to the user and should be maintainable, dependable and usable.

What is software engineering? Software engineering is an engineering discipline that is concerned with all aspects of software production.

What is the difference between software engineering and computer science?

Computer science focuses on theory and fundamentals; software engineering is concerned with the practicalities of developing and delivering useful software.

What is the difference between software engineering and system engineering?

System engineering is concerned with all aspects of computer-based systems development including hardware, software and process engineering. Software engineering is part of this more general process.

Essential attributes of good software

Product characteristic

Description

Maintainability Software should be written in such a way so that it can evolve to meet the changing needs of customers. This is a critical attribute because software change is an inevitable requirement of a changing business environment.

Dependability and security

Software dependability includes a range of characteristics including reliability, security and safety. Dependable software should not cause physical or economic damage in the event of system failure. Malicious users should not be able to access or damage the system.

Efficiency Software should not make wasteful use of system resources such as memory and processor cycles. Efficiency therefore includes responsiveness, processing time, memory utilisation, etc.

Acceptability Software must be acceptable to the type of users for which it is designed. This means that it must be understandable, usable and compatible with other systems that they use.

Software Engineering

In order to build software that meets challenges of 21st century, following must be recognized:

Understand the problem before you build a solution

Design is a pivotal software engineering activity

Both quality and maintainability are an outgrowth of good design

How do we define software engineering? Software engineering is a layered technology:

A Layered Technology

A quality Process     Any engineering approach must rest on an quality. The "Bed Rock" that supports software Engineering is Quality

focus

Process Foundation for SE is the Process Layer SE process is the GLUE that holds all the technology layers

together and enables the timely development of computer software.

It forms the base for management control of software project in which:

technical methods are applied, work products(models, documents, data , reports, forms etc)are produced, milestones, quality is ensured & change is properly managed.

A Layered Technology

Methods SE methods provide the "Technical Questions" for

building Software. Methods contain a broad array of tasks that include

communication, requirement analysis, design, modeling, program construction, testing and support.

Tools SE tools provide automated or semi-automated

support for the "Process" and the "Methods". Tools are integrated so that information created by

one tool can be used by another.

Elements of Software Process Process is a collection of:

Activities Strives to achieve a broad objectives e.g.

communication with stakeholders regardless of project size, application domain, complexity of effort

Elements of Software Process Actions

Consists of set of tasks that produces a major work product i.e.

Architectural design model

Task Focuses on small , but well defined objectives e.g.

Conducting an unit test to produce tangible outcomes

The Software Process In software engineering, a process is not a rigid

prescription for how to build computer software

Rather, it is adaptable approach that enables people(software teams) to pick and choose appropriate work actions & tasks

The intent is to deliver the software in time and with quality to satisfy those who sponsored its creation and those who will use it(customers).

Software process framework activities Five generic process framework activities are:

Communication communicate with customer to understand objectives and gather

requirements

Planning creates a “map” defines the work by describing the tasks, risks

and resources, work products and work schedule.

Modeling Create a “sketch”, what it looks like architecturally, how the

constituent parts fit together and other characteristics.

Construction code generation and the testing

Deployment Delivered to the customer who evaluates the products and

provides feedback based on the evaluation.

These five framework activities can be used to all software development regardless of the application domain, size of the project, complexity of the efforts etc, though the details will be different in each case.

For many software projects, these framework activities are applied iteratively as a project progresses.

Each iteration produces a software increment that provides a subset of overall software features and functionality.

Cont . . .

Software Myths Describes a number of common beliefs or myths that

software managers, customers, and developers believe falsely

Misleading attitudes that have caused serious problems for managers and practitioners

Managers with software responsibility, like management in most disciplines, are often under pressure to maintain:

Budgets Keep schedules Improve quality

To lessen the pressure the software mangers often grasp at beliefs in software myths.

Management Myths

Management’s Myths Myth: "We already have a book that is full of

standards and procedures for building software. Won't that provide my people with everything they need to know?"

Reality: the book standards may exist, but is it used? Are the practitioners aware of its existence? Is it up to date and complete? Is it streamlined to deliver on time and still maintain quality?

Not used, not up to date, not complete, not focused on quality, time, and money

Myth: "If we get behind, we can add more programmers and catch up"

Reality: software development is not a mechanistic process like manufacturing.

Adding people to a late software project makes it later Training time to newcomers, reduced productive

development effort.

Myth:"If I decide to outsource the software project to a third party, I can just relax and let that firm build it"

Reality: If an organization does not understand that how to manage and control s/w projects internally. It will always struggle when it outsource software projects.

Cont . . .

A customer who requests computer software May be a person at the next desk A technical group Marketing /sales department Or outside company

Customers believes myths about software because S/w managers and practitioners do little to correct misinformation.

Myths lead to false expectation and ultimately dissatisfaction with the developer.

Customer’s Myths

Customer’s Myths g432222432 Myth:"A general statement of objectives is sufficient

to begin writing programs – we can fill in the details later“

Reality: although a comprehensive and stable statement of requirement is not always possible

Ambiguous statement of objectives spells disaster Unambiguous requirement are developed via effective and continuous

communication between the customer and developer.

Myth:"Project requirements continually change, but change can be easily accommodated because software is flexible"

Impact of change depends on where and when it occurs in the software life cycle (requirements analysis, design, code, test)

Myths that are still believed by software practitioners have been forwarded by over 50 years culture.

Early days programming was viewed as an art form.

Old ways and attitude die hard

Practitioner's myths

Practitioner’s Myth Myth:"Once we write the program and get it to work, our

job is done" 60% to 80% of all effort spent on software occurs after it is delivered

to customer. Myth:"Until I get the program running, I have no way of

assessing its quality Formal technical reviews of requirements analysis documents, design

documents, and source code (more effective than actual testing) Myth:"The only deliverable work product for a successful

project is the working program" Software, documentation, test drivers, test results

Myth:"Software engineering will make us create voluminous and unnecessary documentation and will invariably slow us down"

Creates quality, quality reduces rework and provides software on time and within the budget

Phases in Software Development When ever we develop a program or build something,

there are some activities we perform. Requirement Analysis Design Coding Testing

Software Engineering For large software's where the problem solving activities

may last for many years and where many people are involved in development, performing theses activities without proper documentation will not work.

In most commercial software developments there are some activities performed before the analysis requirement takes place called feasibility analysis phase in order to calculate cost and profit.

Software Engineering

Requirement Analysis Requirement analysis is done in order to understand the

problem which the software system is to solve.

The problem could be automating an existing manual system or developing a new system

For large system where there are a lot of features, understanding the requirement is a major problem.

Software Engineering In this phase the emphasis is given on identifying what is

needed from the system and not how the system will achieve the goals

Two parties are involved in this process A client ………… A developer

Software Engineering There are two major activities in this phase

Problem understanding or analysis and requirement specification (software Requirement specification)

This phase ends with the validation of the requirements specified in the document.

Software Engineering Software Design

The purpose of the design phase is to plan a solution of the problem specified by the requirement document.

Design stage takes us towards how to satisfy the needs.

Most important part of the software Blue print of the software

Software Engineering The design activity is often divided into two parts

System design Detailed design

This phase produces a design document Partitioning and Abstraction Validation

Software Engineering Coding

The goal of this phase is to translate the design into a code in a given Language

The coding phase affects both the testing and maintenance phase.

Single entry------Single exit construct

Software Engineering Testing

Testing is the major control measure employed during software development

Its basic purpose is to detect errors in the software. Unit testing Integration testing System Testing

Software Engineering For testing to be successful, proper selection of test cases

are essential.

Test Plan: It identifies all the testing activities that must be

performed and specifies the schedule, cost, resources, different units to be tested and the manner in which all the modules will be integrated, different test cases etc.

Software Engineering Maintenance

It is not a part of software development but extremely important activity in software product.

It always start after the software is delivered to the customer

Two major forms of maintenance are Adaptive maintenance Corrective maintenance

Adaptive maintenance: Over time the original environment e.g OS, CPU or

other business rules for which the software was developed is likely to change.

So adaptive maintenance results in modification of s/w to accommodate such changes to its external environment.

Corrective maintenance When the customer is using the software he is likely to

uncover defects and the correction of such changes will come under corrective maintenance.

Cont . . .