NSCET E-LEARNING PRESENTATION NOTES/unit 1/CS8494_SE.pdf · o software must be adapted to meet the needs of new computing environments or technology. o software must be enhanced to

NSCET

E-LEARNING

PRESENTATION

LISTEN … LEARN… LEAD…

1 Department of CSE, NSCET, Theni

COMPUTER SCIENCE AND ENGINEERING

Mr.C.PRATHAP M.Tech.,(Phd).,

Assistant Professor

Nadar Saraswathi College of Engineering & Technology,

Vadapudupatti, Annanji (po), Theni – 625531.

CS8494 – SOFTWARE ENGINEERING

II YEAR / IV SEMESTER

PHOTO


UNIT 01 - SOFTWARE PROCESS

AND

AGILE DEVELOPMENT

Department of CSE, NSCET, Theni

Introduction to

Software

Engineering

01.


Let us first understand what software

engineering stands for.

The term is made of two words,

Software and Engineering.


Software • Software is more than just a program code. • A program is an executable code, which serves some computational purpose. • Software, when made for a specific requirement is called software product.


Engineering • Engineering on the other hand, is all

about developing products, using well-defined, scientific principles and methods.


Software engineering • Software engineering is an engineering branch associated with development of

software product using well-defined scientific principles, methods and procedures. The outcome of software engineering is an efficient and reliable software product.


Definitions IEEE defines software engineering as:

• The application of a systematic, disciplined, quantifiable approach to the development , operation and maintenance of software; that is, the application of engineering to software.


Need of Software Engineering

• Why does it take so long to get software finished?

• Why are development costs so high?

• Why can’t we find all errors before we give the software to our customers?

• Why do we spend so much time and effort maintaining existing programs?

• Why do we continue to have difficulty in measuring progress as software is being developed and maintained?


Characteristics of Good Software

• A software product can be judged by what it offers and how well it can be used. This software must

satisfy on the following grounds: • Operational • Transitional • Maintenance


Operational •This tells us how well software works in operations. It can be measured on:

• Budget

• Usability

• Efficiency

• Correctness

• Functionality

• Dependability

• Security

• Safety


Transitional This aspect is important when the software is moved from one platform to another:

• Portability

• Interoperability

• Reusability

• Adaptability


Maintenance This aspect briefs about how well a software has the capabilities to maintain itself in the ever-changing

environment:

• Modularity

• Maintainability

• Flexibility

• Scalability


Software Characteristics

• Software is developed or engineered, it is not manufactured in the classical sense.



• Software doesn't

"wear out.“



• Although the industry is moving toward component-based assembly

• Most of software is custom build rather than

• assemble from existing component.

• Easy to modify

• Easy to Reproduce


Software Applications

• system software

• application software

• engineering/scientific software

• embedded software

• WebApps (Web applications)

• AI software


Software—New Categories

• Open world computing—pervasive, distributed computing

• Ubiquitous computing—wireless networks

• Netsourcing—the Web as a computing engine

• Open source—”free” source code open to the computing community


Legacy Software • Why must it change?

o software must be adapted to meet the needs of new computing environments or technology. o software must be enhanced to implement new business requirements.

o software must be extended to make it interoperable with other more modern systems or databases.

o software must be re-architected to make it viable within a network environment.


Characteristics of WebApps

• Network intensiveness. A WebApp resides on a network and must serve the needs of a diverse community of clients. • Concurrency. A large number of users may access the WebApp at one time. • Unpredictable load. The number of users of the WebApp may vary by orders of magnitude from day to day. • Performance. If a WebApp user must wait too long (for access, for server-side processing, for client-side formatting and

display), he or she may decide to go elsewhere. • Availability. Although expectation of 100 percent availability is unreasonable, users of popular WebApps often demand

access on a “24/7/365” basis.


Characteristics of WebApps

• Data driven. The primary function of many WebApps is to use hypermedia to present text, graphics, audio, and video content to the end-user.

• Content sensitive. The quality and aesthetic nature of content remains an important determinant of the quality of a WebApp.

• Immediacy. Although immediacy—the compelling need to get software to market quickly—is a characteristic of many application domains, WebApps often exhibit a time to market that can be a matter of a few days or weeks.

• Security. Because WebApps are available via network access, it is difficult, if not impossible, to limit the population of end-users who may access the application.


A Process Framework

• A process framework establishes the foundation for a complete software engineering process by identifying a small number of framework activities that are applicable to all software projects, regardless of their size or complexity.

• In addition, the process framework encompasses a set of umbrella activities that are applicable across the entire software process.


Framework Activities • Communication

• Planning

• Modeling

o Analysis of requirements

o Design

• Construction

o Code generation

o Testing

• Deployment


Umbrella Activities • Software project tracking and control- against the plan

• Formal technical reviews- Conduct activities to remove error

• Software quality assurance -Testing

• Software configuration management – manage the effects of change

• Work product preparation and production –Models

• Reusability management - reuse

• Risk management- assess the risk


The Essence of Practice

• Understand the problem (communication and analysis). • Plan a solution (modeling and software design). • Carry out the plan (code generation). • Examine the result for accuracy (testing and quality assurance).


Understand the Problem

• Who has a stake in the solution to the problem? That is, who are the stakeholders? • What are the unknowns? What data, functions, and features are required to properly solve

the problem? • Can the problem be compartmentalized? Is it possible to represent smaller problems that

may be easier to understand? • Can the problem be represented graphically? Can an analysis model be created?


Plan the Solution • Have you seen similar problems before? Are there patterns that are recognizable in a potential

solution? Is there existing software that implements the data, functions, and features that are required?

• Has a similar problem been solved? If so, are elements of the solution reusable?

• Can subproblems be defined? If so, are solutions readily apparent for the subproblems?

• Can you represent a solution in a manner that leads to effective implementation? Can a design model be created?


Carry Out the Plan

• Does the solution conform to the plan? Is source code traceable to the design model? • Is each component part of the solution provably correct? Has the design and code been

reviewed, or better, have correctness proofs been applied to algorithm?


Examine the Result

• Is it possible to test each component part of the solution? Has a reasonable testing strategy been implemented?

• Does the solution produce results that conform to the data, functions, and features that are required? Has the software been validated against all stakeholder requirements?


Hooker’s General Principles

• 1: The Reason It All Exists

• 2: KISS (Keep It Simple, Stupid!)

• 3: Maintain the Vision

• 4: What You Produce, Others Will Consume

• 5: Be Open to the Future

• 6: Plan Ahead for Reuse

• 7: Think!


The Reason It All Exists

• ALL Decisions should be made with this in mind… • “ Does this add real value to the system?” • If there is no, don’t do it.


KISS (Keep It Simple, Stupid!)

“ALL design should be as possible, but no simpler..”


Maintain the Vision

• “ A clear vision is essential to the success of a software project”

• A project almost unfailingly ends up being “ of two [or more] minds”


What You Produce, Others Will Consume

“ Always specify, design and implement knowing someone else will have to understand what you are doing”


Be Open to the Future

• “ True industrial-strength software systems must endure far longer” • To do this successfully, these systems must be ready to adapt to these and

other changes.


Plan Ahead for Reuse

• “ Achieving a high level of reuse is arguably the hardest goal to accomplish in developing a software system”

• The reuse of code and designs has been proclaimed as a major benefit of using object oriented technologies.


Think!

• Placing clear, complete thought before action almost always produces better results.

• A side effect of thinking is learning to recognize when you don’t know something , at which point you can research the answer.


Process Models

• This Aspect – called process flow • Describes how the frame work activities and the actions and tasks that occur within each

framework activity are organized with respect to sequence and time…


Process Flow


Linear Process flow

• It executes each of the five frame work activities in sequence ,beginning with communication and culminating with deployment…..


Iterative process flow

• It repeats one or more of the activities before proceeding to the next


Evolutionary Process

• It executes the activities in a circular manner • It leads to a more complete version of the software.


Parallel Process flow

• It executes one or more activities in parallel with other activities.


Identifying a Task Set

• A task set defines the actual work to be done to accomplish the objectives of a software engineering action.

o A list of the task to be accomplished

o A list of the work products to be produced

o A list of the quality assurance filters to be applied


Process Patterns

• A process pattern

o describes a process-related problem that is encountered during software engineering work,

o identifies the environment in which the problem has been encountered, and

o suggests one or more proven solutions to the problem.


Prescriptive Models

• Prescriptive process models advocate an orderly approach to software engineering

• That leads to a few questions …

• If prescriptive process models strive for structure and order, are they inappropriate for a software world that thrives on change?

• Yet, if we reject traditional process models (and the order they imply) and replace them with something less structured, do we make it impossible to achieve coordination and coherence in software work?


The Waterfall Model or Classic life cycle model

Communicat ion

Planning

Modeling

Const ruct ionDeployment

analysis

designcode

t est

project init iat ion

requirement gat hering estimating

scheduling

tracking

delivery

support

f eedback


The V-Model


The Incremental Model

C o m m u n i c a t i o n

P l a n n i n g

M o d e l i n g

C o n s t r u c t i o n

D e p l o y m e n t

d e l i v e r y

f e e d b a c k

ana ly s is

des ign c ode

t es t

increment # 1

increment # 2

delivery of

1st increment

delivery of

2nd increment

delivery of

nt h increment

increment # n

project calendar t ime


P l a n n i n g

M o d e l i n g


D e p l o y m e n t

d e l i v e r y

f e e d b a c k

analy s is

des ign c ode

t es t


P l a n n i n g

M o d e l i n g


D e p l o y m e n t

d e l i v e r y

f e e d b a c k

ana ly s is

des ignc ode

t es t


Evolutionary Models: Prototyping

Construction of prototype

Communicat ion

Qu ick p lan

Const ruct ion

of

prot ot ype

Mo d e lin g

Qu ick d e sig n

De live ry

& Fe e dback

Deployment

communication

Quick plan

Modeling Quick design

Construction of prototype

Deployment delivery & feedback


SPIRAL MODEl

• It is the combination of Waterfall and Iterative model. • Each phase in spiral model begins with design goal and ends with client

reviewing. • Software is developed in a series of incremental releases


Evolutionary Models: The Spiral

communication

planning

modeling

construction deployment delivery feedback

start

analysis design

code test

estimation scheduling risk analysis


TASK REGION

• TASK 1 : CONCEPT DEVELOPMENT

• TASK 2 : SYSTEM DEVELOPMENT

• TASK 3 : SYSTEM ENHANCEMENT

• TASK 3 : SYSTEM MAINTENANCE


Detailed Spiral Model


When to use Spiral Model

• When Project is large • When releases are required to be frequent • When risk and cost analysis are important • When requirements are unclear and complex • When Changes may require at any time • For medium to high risk project.


Evolutionary Models: Concurrent

Under review

Baselined

Done

Under

revision

Await ing

changes

Under

development

none

Modeling act ivit y

represents the state

of a sof tware engineering

act ivity or task


Concurrent MODEL

• Its also called Concurrent Engineering • The frame work activities or software development tasks are represented as states. • It is applicable to all types of software development and provides an accurate picture of the

current state of a project.


Specialized Model

• Component based development—the process to apply when reuse is a development objective. S/w reusability , it reduces the time and cost.

• Formal methods—emphasizes the mathematical specification of requirements.

• it overcomes problems like ambiguity, incompleteness and inconsistency.

• AOSD—provides a process and methodological approach for defining, specifying, designing, and constructing aspects


Component Based Model-Steps

• Identify the component based products and analyzed • Analyze the component integration issues. • Design the s/w architecture. • Integrate the components into the s/w architecture. • Conduct the comprehensive testing.


Formal methods- Defect free software

• Yet, concern about its applicability in a business environment has been voiced:

• The development of formal models is currently quite time consuming and expensive.

• Because few software developers have the necessary background to apply formal methods, extensive training is required.

• It is difficult to use the models as a communication mechanism for technically unsophisticated customers.


AOSD • When concerns cut across multiple system functions, features, and information,they are

often referred to as crosscutting concerns.

• Aspectual requirements define those crosscutting concerns that have an impact across the software architecture.

• Aspect-oriented software development (AOSD), often referred to as aspect-oriented programming (AOP), is a relatively new software engineering paradigm that provides a process and methodological approach for defining, specifying, designing, and constructing

aspects.


Unified Process

• “use-case driven, architecture-centric, iterative and incremental” software process closely aligned with the Unified Modeling Language (UML)


The Unified Process (UP)

soft ware increment

Release

Incept ion

Elaborat ion

const ruct ion

t ransit ion

product ion


UP Work Products Incept ion phase

Elaborat ion phase

Const ruct ion phase

Transit ion phase

Vision document

Init ial use-case model

Init ial project glossary

Init ial business case

Init ial risk assessment .

Project plan,

phases and it erat ions.

Business model,

if necessary .

One or more prot ot ypes I n c e p t i o

n

Use-case model

Supplement ary requirement s

including non-funct ional

Analysis model

Soft ware archit ect ure

Descript ion.

Execut able archit ect ural

prot ot ype.

Preliminary design model

Rev ised risk list

Project plan including

it erat ion plan

adapt ed workf lows

milest ones

t echnical work product s

Preliminary user manual

Design model

Soft ware component s

Int egrat ed sof t ware

increment

Test plan and procedure

Test cases

Support document at ion

user manuals

inst allat ion manuals

descript ion of current

increment

Delivered sof t ware increment

Bet a t est report s

General user feedback


UP Phases Incept ion Elaborat ion Const ruct ion Transit ion Product ion

UP Phases

Workflows

Requirements

Analysis

Design

Implementation

Test

Iterations #1 #2 #n-1 #n

Support


The Manifesto for Agile Software Development

“We are uncovering better ways of developing software by doing it and helping others do it. Through this work we have come to value: •Individuals and interactions over processes and tools •Working software over comprehensive documentation •Customer collaboration over contract negotiation •Responding to change over following a plan That is, while there is value in the items on the right, we value the items on the left more.”

Kent Beck et al


What is “Agility”?

o Effective (rapid and adaptive) response to change (team members, new technology,

requirements)

o Effective communication in structure and attitudes among all team members, technological

and business people, software engineers and managers。

o Drawing the customer into the team. Eliminate “us and them” attitude.

o Organizing a team so that it is in control of the work performed

o Planning in an uncertain world has its limits and plan must be flexible

o Eliminate all but the most essential work products and keep them lean

o Emphasize an incremental delivery strategy as opposed to intermediate products that gets

working software to the customer as rapidly as feasible


What is “Agility”? Yielding …

Rapid, incremental delivery of software

The development guidelines stress delivery over analysis and design although these activates are not discouraged, and active and continuous communication between developers and customers.


Why and What Steps are“Agility”

Why? The modern business environment is fast-paced and ever-changing. It represents a reasonable alternative to conventional software engineering for certain classes of software projects. It has been demonstrated to deliver successful systems quickly.

What? May be termed as “software engineering lite” The basic activities- communication, planning, modeling, construction and deployment remain. But they morph into a minimal task set that push the team toward construction and delivery sooner. The only really important work product is an operational

“software increment” that is delivered.


Agility and the Cost of Change

Conventional wisdom is that the cost of change increases nonlinearly as a project progresses. It is relatively easy to accommodate a change when a team is gathering requirements early in a project. If there are any changes, the costs of doing this work are minimal. But if the middle of validation testing, a stakeholder is requesting a major functional change. Then the change requires a modification to the architectural design, construction of new components, changes to other existing components, new testing and so on. Costs escalate quickly.

A well-designed agile process may “flatten” the cost of change curve by coupling incremental delivery with agile practices such as continuous unit testing and pair programming. Thus team can accommodate changes late in the software project without dramatic cost and time impact.


Agility and the Cost of Change


An Agile Process Is driven by customer descriptions of what is required

(scenarios). Some assumptions:

Recognizes that plans are short-lived (some requirements will persist, some will change. Customer priorities will change)

Develops software iteratively with a heavy emphasis on construction activities (design and construction are interleaved, hard to

say how much design is necessary before construction. Design models are proven as they are created. )

Analysis, design, construction and testing are not predictable.

Thus has to Adapt as changes occur due to unpredictability

Delivers multiple ‘software increments’, deliver an operational prototype or portion of an OS to collect customer feedback for adaption.


Agility Principles - I 1. Our highest priority is to satisfy the customer through early and continuous delivery of valuable software.

2. Welcome changing requirements, even late in development. Agile processes harness change for the customer's competitive advantage.

3. Deliver working software frequently, from a couple of weeks to a couple of months, with a preference to the shorter timescale.

4. Business people and developers must work together daily throughout the project.

5. Build projects around motivated individuals. Give them the environment and support they need, and trust them to get the job done.

6. The most efficient and effective method of conveying information to and within a development team is face–to–face conversation.


Agility Principles - II

7. Working software is the primary measure of progress.

8. Agile processes promote sustainable development. The sponsors, developers, and users should be able to maintain a constant pace indefinitely.

9. Continuous attention to technical excellence and good design enhances agility.

10. Simplicity – the art of maximizing the amount of work not done – is essential.

11. The best architectures, requirements, and designs emerge from self–organizing teams.

12. At regular intervals, the team reflects on how to become more effective, then tunes and adjusts its behavior accordingly.


Human Factors The process molds to the needs of the people and team, not the other way around

key traits must exist among the people on an agile team and the team itself: Competence. ( talent, skills, knowledge)

Common focus. ( deliver a working software increment )

Collaboration. ( peers and stakeholders)

Decision-making ability. ( freedom to control its own destiny)

Fuzzy problem-solving ability.(ambiguity and constant changes, today problem may not be tomorrow’s problem)

Mutual trust and respect.

Self-organization. ( themselves for the work done, process for its local environment, the work schedule)


Extreme Programming (XP) The most widely used agile process, originally proposed by Kent Beck in 2004. It uses an object-oriented approach.

XP Planning Begins with the listening, leads to creation of “user stories” that describes required output, features, and functionality. Customer assigns

a value(i.e., a priority) to each story.

Agile team assesses each story and assigns a cost (development weeks. If more than 3 weeks, customer asked to split into smaller stories)

Working together, stories are grouped for a deliverable increment next release.

A commitment (stories to be included, delivery date and other project matters) is made. Three ways: 1. Either all stories will be implemented

in a few weeks, 2. high priority stories first, or 3. the riskiest stories will be implemented first.

After the first increment “project velocity”, namely number of stories implemented during the first release is used to help define subsequent delivery dates for other increments. Customers can add stories, delete existing stories, change values of an existing story, split stories as development work proceeds.


Extreme Programming (XP) XP Design ( occurs both before and after coding as refactoring is encouraged)

Follows the KIS principle (keep it simple) Nothing more nothing less than the story.

Encourage the use of CRC (class-responsibility-collaborator) cards in an object-oriented context. The only design work product of XP. They identify and organize the classes that are relevant to the current software increment. (see Chapter 8)

For difficult design problems, suggests the creation of “spike solutions”—a design prototype for that portion is implemented and evaluated.

Encourages “refactoring”—an iterative refinement of the internal program design. Does not alter the external behavior yet improve the internal structure. Minimize chances of bugs. More efficient, easy to read.

XP Coding

Recommends the construction of a unit test for a story before coding commences. So implementer can focus on what must be implemented to pass the test.

Encourages “pair programming”. Two people work together at one workstation. Real time problem solving, real time review for quality assurance. Take slightly different roles.

XP Testing

All unit tests are executed daily and ideally should be automated. Regression tests are conducted to test current and previous components.

“Acceptance tests” are defined by the customer and executed to assess customer visible functionality


Extreme Programming (XP)

unit test

continuous integration

acceptance testing

user stories

values

acceptance test criteria

iteration plan

simple design

CRC cards

spike solutions

prototypes

refactoring

pair programming

Release

software increment

project velocity computed


The XP Debate Requirements volatility: customer is an active member of XP team, changes to requirements are requested informally and frequently.

Conflicting customer needs: different customers' needs need to be assimilated. Different vision or beyond their authority.

Requirements are expressed informally: Use stories and acceptance tests are the only explicit manifestation of requirements. Formal models may avoid inconsistencies and errors before the system is built. Proponents said changing nature makes such models obsolete as soon as they are developed.

Lack of formal design: XP deemphasizes the need for architectural design. Complex systems need overall structure to exhibit quality and maintainability. Proponents said incremental nature limits complexity as simplicity is a core value.


Adaptive Software Development (ASD) Originally proposed by Jim Highsmith (2000) focusing on human collaboration and team self-organization as a technique to build complex software and system.

ASD — distinguishing features Mission-driven planning

Component-based focus

Uses “time-boxing” (See Chapter 24)

Explicit consideration of risks

Emphasizes collaboration for requirements gathering

Emphasizes “learning” throughout the process


Three Phases of ASD

1. Speculation: project is initiated and adaptive cycle planning is conducted. Adaptive cycle planning uses project initiation information- the customer’s mission statement, project constraints (e.g. delivery date), and basic requirements to define the set of release cycles (increments) that will be required for the project. Based on the information obtained at the completion of the first cycle, the plan is reviewed and adjusted so that planned work better fits the reality.


Three Phases of ASD 2. Collaborations are used to multiply their talent and creative output beyond absolute number (1+1>2). It encompasses communication and teamwork, but it also emphasizes individualism, because individual creativity plays an important role in collaborative thinking.

It is a matter of trust. 1) criticize without animosity, 2) assist without resentments, 3) work as hard as or harder than they do. 4) have the skill set to contribute to the work at hand, 5) communicate problems or concerns in a way that leas to effective action.

3. Learning: As members of ASD team begin to develop the components, the emphasis is on “learning”. Highsmith argues that software developers often overestimate their own understanding of the technology, the process, and the project and that learning will help them to improve their level of real understanding. Three ways: focus groups, technical reviews and project postmortems.


Adaptive Software Development

adaptive cycle planning

uses mission statement

project constraints

basic requirements

time-boxed release

plan

Requirements gathering

JAD

mini-specs

components

implemented/tested focus

groups for feedback formal

technical reviews

postmortems

software increment

adjustments for subsequent cycles

Release


Dynamic Systems Development Method

• Active user involvement is imperative.

• DSDM teams must be empowered to make decisions.

• The focus is on frequent delivery of products.

• Fitness for business purpose is the essential criterion for acceptance of deliverables.

• Iterative and incremental development is necessary to converge on an accurate business solution.

• All changes during development are reversible.

• Requirements are baselined at a high level

• Testing is integrated throughout the life-cycle.


Dynamic Systems Development Method

DSDM Life Cycle (with permission of the DSDM consortium)


Scrum A software development method Originally proposed by Schwaber and Beedle (an activity occurs during a rugby match) in early 1990.

Scrum—distinguishing features

Testing and documentation are on-going as the product is constructed Development work is partitioned into “packets”

Work units occurs in “sprints” and is derived from a “b acklog” of existing changing prioritized requirements

Changes are not introduced in sprints (short term but stable) but in backlog.

Meetings are very short (15 minutes daily) and sometimes conducted without chairs ( what did you do since last meeting? What obstacles are you encountering? What do you plan to accomplish by next meeting?)

“demos” are delivered to the customer with the time-box allocated. May not contain all functionalities. So customers can evaluate and give feedbacks.


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NSCET E-LEARNING PRESENTATION NOTES/unit 1/CS8494_SE.pdf · o software must be adapted to meet the needs of new computing environments or technology. o software must be enhanced to