introductiontosoftwareengineering-100410000635-phpapp01

7/28/2019 introductiontosoftwareengineering-100410000635-phpapp01

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Software is (1) instructions (computer programs) that when executed provide

desired features, function, and performance; (2) data structures that enable the

programs to adequately manipulate information; and (3) documents that describe

the operation and use of the programs.

Software Characteristics:

1. Software is developed or engineered; it is not manufactured in the classical

sense.

2. Software does not wear out

Wear out

Infant mortality

Failure curve for hardware

Increased failure rate due to side effects

Change Actual Curve

Idealized curve

Failure curve for software

3. Most software continue to be custom built

Types of Software

1. System Software is a collection of programs written to service other

programs. E.g. compilers, editors and file management utilities.

2. Application Software consists of standalone programs that solve a specific

business need


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3. Engineering/ Scientific software

4. Embedded software resides within a product or system and is used to

implement and control features and functions for the end user and for the

system itself

5. Product-line software are designed to provide a specific capability for use

by many different customers, product line software can focus o a limited

and esoteric marketplace.

6. Web-applications can be a little more than a set of linked hypertext files

that present information using text and limited graphics.

7. Artificial intelligence software makes use of non-numerical algorithms to

solve complex problems that are not amenable to computation or

straightforward analysis.

8. Legacy software

Nature of Software

1. Software is flexible, or open for changes

2. Software is developed for long term usage

3. Software is complex

4. Software involves communication with the machine

Software Engineering is the establishment and use of sound engineering

principles in order to obtain economically software that is reliable and works

efficiently on real machines. It is a layered technology.

The engineering approach must rest on an organizational commitment to

quality. The foundation of software engineering is the process layer, which

defines a framework for effective delivery of software engineering

technology. Methods provide the technical how-tos for building software.

Software engineering tools provide automated or semi-automated support for

the process and methods.


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Software engineering is about solving problems. It can be broken into

analyzing (problem) and synthesis (solution).

Evolution of Software Engineering

Emergence of Software Engineering

Computer Science Customer

Software

Engineering

Tools and

techniques to solve

problems

ProblemComputer

functions

Theories

Art

Craft

Engineering

Esoteric use of past

experience

Unorganized use of

past experience Systematic use of past

experience . Formulation

of scientific basis

Time

T

ec

h

n

o

l

o

g

y


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Software Engineering Challenges

1. Scale: Rules for small scale do not apply on large scale

2. Quality and productivity: These are the terms that are vaguely defined.Productivity directly depends upon the people in development. Quality

includes N number of parameters.

3. Consistently and repeatability: The methods for software development should

be repeatable across projects leading to consistency in the quality of

software produced.

4. Change: Software should accommodate and embrace change. Since as

businesses change, they require that the software supporting it should

change.

5. Heterogeneity: Developing techniques for building software that can cope

with heterogeneous platforms and execution environments;6. Delivery: Developing techniques that lead to faster delivery of software;

7. Trust: Developing techniques that demonstrate that software can be trusted

by its users.

What is good software?

Good software includes a few qualities that can be grouped into the followingcategories.

1. Quality of product

2. Quality of the process3. Quality in the context of business environment (ROI or Return On Investment)Essential qualities of a good software include correctness, reliability, robustness,performance, usability, verifiability, maintainability, repair ability, evolve ability,portability, understandability, interoperability, productivity, timeliness, visibility andreusability, to name a few.

Measurable Characteristics for Software

Object Oriented Design

Data Flow Oriented

Design

Exploratory Style

Control Flow Oriented Design

Data Structure Oriented Design


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1. Functionality: The capability to provide functions which meet stated andimplied needs (suitability) when the software is used, accuracy and security.

2. Reliability: The capability to maintain a specified level of performance3. Usability: The capability to be understood (understandability), learned (learn

ability) and used (operability)4. Efficiency: The capability to provide appropriate performance relative to the

amount of resources used.5. Maintainability: The capability to be modified for purposes of making

corrections (changeability, testability), improvements, or adaptation(stability)

6. Portability: The capability to be adopted (adaptability) for different specifiedenvironments (install ability) without applying actions or means other thanthose provided for this purpose in the product.

Software crisis

There is a rise in software prices as compared to hardware prices. Also the software

is difficult to alter, debug and enhance. This is because of lack of adequate training

in software engineering. Large software has failed and has caused huge losses and

was called software runways.

Reasons for software Crisis

1. Lack of communication between developers and users2. Increase in size of software3. Increase in cost of developing software4. Increased complexity of problems5. Lack of understanding of problem and environment6. High optimistic estimates

7. Difficult estimation of time8. Quality parameters not standardized9. Maintenance problems with code

Software process

Software projects utilize a process to organize the execution of tasks to

achieve the goals on the cost, schedule and quality fronts.

A process model specifies a general process, usually as a set of stages in

which a project should be divided; the order in which the stages should be executed

and any other constraints and conditions on the execution of stages. A projectsprocess may utilize some process model.

The process that deals with the technical and management issues of software

development is called a software process.

The desired Characteristics of a Software Process are:


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1. Predictability: It determines how accurately the outcome of following the

process can be predicted. The fundamental basis for quality prediction is

that quality of the product is determined largely by the process followed

for developing it. Effective management of quality control activities

depends upon the predictability of the process.

2. Support Testability and Maintainability: One of the most importantobjectives of software development should be to reduce the maintenance

effort. The process used, should ensure that maintainability. Both testing

and maintenance depend heavily on the quality of design and code, and

these costs can be considerably reduced if the software is designed and

coded to make testing and maintenance easier.

3. Support change: Software changes are driven by business need, peoples

mindset etc. Thus change is prevalent, and a process that can handle

change easily is desirable.

4. Early Defect removal: We should attempt to detect errors that occur in a

phase, during that phase itself, to reduce effort and cost or removing

them. Error detection and correction should be a continuous process.

5. Process improvement and feedback: To satisfy the objectives of quality

improvement are cost reduction, the software process must be improved.

Software Components

In engineering disciplines, products are always constructed from parts or

components. Similarly, software engineering is component based. Until the early

1990s, components were routines and libraries. With advances in programming

languages, other mechanisms like generic constructs in languages as ADA and C++

and objects and frameworks in object oriented language also came.

A framework is a collection of related classes that are designed to be used

together in developing applications in a certain domain. Standard template library

in C++ is fine grained, code level component. While swing and Java Beans that

provide classes and objects for visual approach to software development are

medium grained components. Large grained components such as database

management systems act as components in the architecture.

A component is a software element that confirms to a component model and

can be independently deployed and composed without modification, according to a

composition standard. Components are standardized, Independent, comparable,

deployable and documented.

Software Costs

Software costs often dominate computer system costs. The costs of

software on a PC are often greater than the hardware costs.


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Software costs more to maintain than it does to develop. For systems

with a long life, maintenance costs may be several times development

costs.

Software engineering is concerned with cost-effective software

development.

Cost of the software includes the cost of developers, the hardware

resources used for development and the cost of infrastructure required

for such development.

Thus following points become important considerations for software engineering

Attempt to estimate cost/effort

Define plan

Prepare schedules

Involve user

Identify stages

Define milestones

Reviews

Define deliverables

Quality assurance steps (testing)

Job of a Software developer

Every developer has to become accurate in three forms of communication

1. Communication with the user. The user is not always well informed. There is

also a gap between the user and the developer in terms of field of work. Thus

getting the right information from the user is very critical task for the

developer

2. Communication with the technical specialists. It is difficult to understand the

jargon of a technical specialist and thus the developer has to convey the

information correctly to him, in the way he can understand.

3. Communication with the management. The management personnel have

business knowledge and understanding of the application of the software. But

they are not well versed with the technicalities involved. Judging correctly the

importance of the requirement stated by the management is an important

task for the developer.

Software Engineering Code of Ethics

The preamble of the code states that


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Computers have a central and growing role in commerce, industry, government,

medicine, education, entertainment, and society at large. Software engineers are

those who contribute by direct participation or by teaching, to the analysis,

specification, design, development, certification, maintenance, and testing of

software systems. Because of their roles in developing software systems, software

engineers have significant opportunities to do good or cause harm. To ensure, asmuch as possible, that their efforts will be used for good, software engineers must

commit themselves to making software engineering a beneficial and respected

profession.

Software engineers shall commit themselves to making the analysis, specification,

design, development, testing and maintenance of software a beneficial and

respected profession. In accordance with their commitment to the health, safety

and welfare of the public, software engineers shall adhere to the following Eight

Principles:

The eight principles are as follows:

1. Public: Software engineers shall act consistently with the public interest.

2. Client and Employer: Software engineers shall act in a manner that is in the best

interests of their client and employer, consistent with the public interest.

3. Product: Software engineers shall ensure that their products and related

modifications meet the highest professional standards possible.

4. Judgment: Software engineers shall maintain integrity and independence in their

professional judgment.

5. Management: Software engineering managers and leaders shall subscribe to and

promote an ethical approach to the management of software development and

maintenance.6. Profession: Software engineers shall advance the integrity and reputation of the

profession, consistent with the public interest.

7. Colleagues: Software engineers shall be fair to, and supportive of, their

colleagues.

8. Self: Software engineers shall participate in lifelong learning regarding the

practice of their profession and shall promote an ethical approach to the practice of

the profession.

Software Metrics are quantifiable measures that could be used in Software

engineering to calculate1. The complexity of the software which in turn helps in other ways

2. Cost estimation based on the calculations

3. Allocation of appropriate resources as per the complexity of project

4. Correct scheduling of tasks as per the complexity

5. Evaluation of Quality and reliability of system

6. Improving quality of the system

7. Help in management of risks


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They help in the overall development of the system in a more organized and

methodical way. Metrics are important to manage the project successfully. There

are three types of software metrics:

1. Product metrics measure the software

2. Process metrics quantify characteristics of the process used

3. Project metrics quantifies the whole project such as amount of projectcompletion

There are different scales for measuring metrics such as:

1. Nominal which categorizes in groups and is thus a qualitative and not a

quantitative measure

2. Ordered scale and tell the sequence

3. Interval can be incremental or regression analysis

4. Ratio can tell exact quantitative differences which can be ordered and

grouped

Examples: Measures are of different types

1. Size metrics

a. LOC

b. ELOC/NLOC

c. CLOC

d. Functionality

e. Effort

2. Function points

3. Complexity

a. O notation

b. Algorithm/ logic4. Structure

a. Cyclomatic complexity

5. Process measurement

a. Time taken for process activities to be

completed E.g. Calendar time or effort to complete an activity or

process.

b. Resources required for processes or activities E.g. Total effort in

person-days.

c. Number of occurrences of a particular event E.g. Number of defects

discovered.


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Issue Software Engineering Engineering

Foundations

Based on computer science,

information science, and discrete

mathematics.

Based on science, mathematics, and empirical

knowledge.

Cost

Compilers and computers arecheap, so software engineering

and consulting are often more

than half of the cost of a project.Minor software engineering

cost-overruns can adverselyaffect the total project cost.

In some projects, construction and

manufacturing costs can be high, so engineering

may only be 15% of the cost of a project. Majorengineering cost overruns may not affect the

total project cost.

Replication

Replication (copying CDs ordownloading files) is trivial.

Most development effort goes

into building new (unproven) or

changing old designs and addingfeatures.

Radically new or one-of-a-kind systems canrequire significant development effort to create a

new design or change an existing design. Other

kinds of systems may require less development

effort, but more attention to issues such asmanufacturability.

Innovation

Software engineers often apply

new and untested elements insoftware projects.

Engineers generally try to apply known and

tested principles, and limit the use of untestedinnovations to only those necessary to create a

product that meets its requirements.

Duration

Software engineers emphasize

projects that will live for years

or decades.

Some engineers solve long-ranged problems

(bridges and dams) that endure for centuries.

Management

Status

Few software engineers manage

anyone.

Engineers in some disciplines, such as civil

engineering, manage construction,

manufacturing, or maintenance crews.

Blame Software engineers must blame Engineers in some fields can often blame


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themselves for project problems.construction, manufacturing, or maintenance

crews for project problems.

Practitionersin U.S.

611,900 software engineers 1,157,020 total non-software engineers

AgeSoftware engineering is about 50years old.

Engineering as a whole is thousands of yearsold.

Title

Regulations

Software engineers are typically

self-appointed. A computer

science degree is common but

not at all a formal requirement.[

In many jurisdictions it is illegal to call yourself

an engineer without specific formal education

and/or accreditation by governmental or

engineering association bodies.

Analysis

Methodology

Methods for formally verifying

correctness are developed incomputer science, but they are

rarely used by software

engineers. The issue remainscontroversial.

Some engineering disciplines are based on a

closed system theory and can in theory prove

formal correctness of a design. In practice, a lackof computing power or input data can make such

proofs of correctness intractable, leading many

engineers to use a pragmatic mix of analyticalapproximations and empirical test data to ensure

that a product will meet its requirements.

Synthesis

Methodology

SE struggles to synthesize (build

to order) a result according to

requirements.

Engineers have nominally refined synthesis

techniques over the ages to provide exactly this.

However, this has not prevented some notableengineering failures, such as the collapse of

Galloping Gertie (the original Tacoma Narrows

Bridge), the sinking of the Titanic, and thePentium FDIV bug. In addition, new

technologies inevitably result in new challenges

that cannot be met using existing techniques.

Researchduring

Projects

Software engineering is oftenbusy with researching the

unknown (e.g. to derive an

algorithm) right in the middle ofa project.

Traditional engineering nominally separatesthese activities. A project is supposed to apply

research results in known or new clever ways to

build the desired result. However, ground-breaking engineering projects such as Project


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Apollo often include a lot of research into the

unknown.

Codified Best

Practice

Software engineering has justrecently started to codify and

teach best practice in the form of

design patterns.

Some engineering disciplines have thousands ofyears of best practice experience handed overfrom generation to generation via a field's

literature, standards, rules and regulations.

Newer disciplines such as electronic engineeringand computer engineering have codified their

own best practices as they have developed.


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Software Development Life Cycle

The software Life Cycle encompasses all activities required to define, develop, test

deliver, operate and maintain a software product. Planning the software

development process involves several important considerations. The first is to

define a product life cycle model. The SDLC activities are:

1. Feasibility: Determine if the software has significant contribution tobusiness. It includes market analysis if similar software is in demand inmarket. Software is evaluated on the basis of cost, schedule and quality.

2. Requirements are determined such as functional properties desired byusers, system requirements such as availability, performance and safety,establishing set of objectives the system should meet, characteristics thatthe system should not exhibit. Such requirements are obtained by variousmethods such as interviews, communication with stake holders, scenariodiscussions, use cases and ethnography. These requirements are thenverified and tested.

3. Project Planning, cost analysis, scheduling, quality assurance plans aremade

4. Designing i.e. Architectural design, Interface design and detailed design5. Implementation includes writing the code for the project as per the designs

and plan6. Testing ensures accuracy and reliability7. Delivery, Installation, Training, Help Desk8. Maintenance, software configuration management.

Another view of SDLC emphasizes the milestone, documents and reviews

throughout product development. It is difficult for project managers to assess

progress or anticipate problems. Establishing milestones, improves product

visibility. The following are the milestones for the project.

1. Feasibility report2. System definition, project plan3. Software requirement specification, Preliminary user manual

4. Architectural design document5. Detailed design document6. Software verification plan7. Product Schedule8. Software test plan, Acceptance test9. Software quality assurance plan10.User manual11.Source code12.Test results


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13.Defect report

Every software engineering organization should describe a unique set of

framework activities for the software process it adopts. Various models have beendeveloped over the years to accommodate these activities.

Models for Software Development

Evolutionary models

1. Waterfall Model suggests a systematic sequential approach to softwaredevelopment that begins with customer specification of requirements. Theprinciple stages of the model map onto fundamental development activities.

a. Requirement Analysis and definitionb. System and software designc. Implementation and unit testingd. Integration and system testinge. Operation and maintenance


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The verification at each stage ensures that the output is consistent with its input

and overall requirement of the system. These outputs are often called work

products and can be listed as:

a. Requirements documents

b. Project plan

c. Design documents

d. Test plan and test reports

e. Final code

f. Software manuals (e.g. user, installation, etc)

Advantages

1. Simple method with clear steps

2. Easy to administer as it is systematic


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3. Verification at each stage ensures early detection of errors /

misunderstanding

4. Documentation helps in future maintenance and revisions

Disadvantage

1. Unchanging requirements are not realistic

2. Document driven process

3. Change adaptability is very slow

2. Incremental Model: Customer identifies the services to be provided. Thedelivery increments are then defined, with each increment providing a sub-set of the system functionality. Once the system increments for the serviceshave been identified, the requirements to be delivered in the first incrementare defined in detail and the increment is developed.

3. Prototyping: First a working prototype of the software is developed instead ofdeveloping the actual software. The developers use this prototype to refinethe requirements and prepare final specification document. After thefinalization of SRS document, the prototype is discarded and actual system isthen developed using the waterfall approach.

Define

outline

requirement

Assign

requirement

s to

increments

Design

System

Architecture

Develop

System

incremen

t

Validate

Incremen

t

Integrate

Increment

Validate

SystemFinal

System


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There are 2 types of prototypes; throw-away, where the initial prototype is

discarded after the requirements are defined and the evolutionary prototype,

where the system is built further on the prototype itself. A prototype is built

for those requirements which are critical for the project and are notunderstood well. If the number of requirements which need clarification is

more, then a working prototype is built for them. The importance or criticality

of such requirements is also a significant factor in determining the need of a

prototype.

Advantages of Prototyping

1. Users are actively involved in the development2. It provides a better system to users, as users have natural tendency to

change their mind in specifying requirements and this method of developingsystems supports this user tendency.

3. Since in this methodology a working model of the system is provided, theusers get a better understanding of the system being developed.

4. Errors can be detected much earlier as the system is mode side by side.

5. Quicker user feedback is available leading to better solutions.

Requirements

Quick Design / Prototype

Implement

Customer Evaluation

Design

Implementation and Unit Testing

Integration and System Testing

Operation and Maintenance

Refinement of

Requirements as

per suggestions


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Disadvantages

1. Leads to implementing and then repairing way of building systems.2. Practically, this methodology may increase the complexity of the system as

scope of the system may expand beyond original plans.

4. Spiral Model: Boehm tried to incorporate the project risk factor into a lifecycle model. Each phase is split roughly into four sections namely planning,

risk analysis, development and assessment. There are 4 phases namelyfeasibility, requirements analysis, design and coding and testing.

The development spiral consists of four quadrants as shown in the figure aboveThe first step in each phase is to identify the objective, alternatives and constraints

of that phase. The next stage involves identifying the best alternative, by


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comparing all and performing risk analysis. One the alternative is chose, prototypes

are built using simulation and benchmarks. Each phase is completed with a review

by the people concerned with the project.

Specialized process models

1. Extreme programming includes creating a set of stories and assigning theirpriority. The commitment defines the order for development. The objects areorganized for development. Designing occurs both after and beforeprogramming, in the form of design and refactoring. Programming happens inthe form of pain programming where two people work together at one

workstation. Writing test cases before starting the coding is a key feature ofextreme programming. Acceptance testing is followed by system testing.

2. Component-Based Development uses commercial-off-the-shelf (COTS)software components.

3. Unified Process is a use-case driven, architecture centric, iterative andincremental software process.

4. Dynamic Systems Development Method (DSDM) suggests an iterativesoftware process. After the feasibility study follows the business study thatestablishes the functional and information requirements for the application.

The iteration steps include Functional model iteration which creates aprototype. New requirements might be generated through the prototype, bythe user. Subsequently or simultaneously designs are built or rebuilt.Implementation iteration places the latest software increments.

5. Feature driven development emphasizes project management guidelines andtechniques. The processes defined for such development are to develop anoverall model, build a feature list, plan by feature, design by feature, build byfeature..

Process improvement

Process improvement is about understanding existing processes and introducing

process changes to improve product quality reduce costs or accelerateschedules. Most process improvement work so far has focused on defect

reduction. This reflects the increasing attention paid by industry to quality.

However, other process attributes can also be the focus of improvement.

Feedback is important for process improvement to initiate.


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Why is it difficult to improve a software process?

1. Not enough time: Developers, because of unrealistic schedules are left withno time to explore problems of development and find solutions.

2. Lack of knowledge: many developers are not aware of best practices3. Wrong motivation: The basic motivation should be to eradicate current

difficulties and not just to achieve a higher CMM level.4. Insufficient commitment

Process

Improvement

Begins Improved future state

Do not quit here

Learning curve

Time

Process improvement stages

Process measurement

Attributes of the current process are measured. These are a baseline for

assessing improvements.

Process analysis

The current process is assessed and bottlenecks and weaknesses are

identified.

Process change

Pro

du

cti

vit

y


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Changes to the process that have been identified during the analysis are

introduced.

Process choice

Process used should depend on type of

product which is being developed

For large systems, management is usually the principal problem so youneed a strictly managed process;

For smaller systems, more informality is possible.There is no uniformly applicable process which

should be standardised within an organisation

High costs may be incurred if you force an inappropriate process on adevelopment team;

Inappropriate methods can also increase costs and lead to reducedquality.

Process analysis and modelling

1. Study an existing process to understand its activities.2. Produce an abstract model of the process. You should normally represent this

graphically. Several different views (e.g. activities, deliverables, etc.) may berequired.

3. Analyse the model to discover process problems. This involves discussingprocess activities with stakeholders and discovering problems and possibleprocess changes.

Process analysis techniques

Published process models and process standards: It is always best to start

process analysis with an existing model. People then may extend and changethis.

Questionnaires and interviews: Must be carefully designed. Participants may

tell you what they think you want to hear.


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Ethnographic analysis: Involves assimilating process knowledge by

observation. Best for in-depth analysis of process fragments rather than forwhole-process understanding.

Process change stages

Improvement identification.

Improvement prioritization.

Process change introduction.

Process change training.

Change tuning.

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