software engineering process model

Text Books:1.Software Engineering, A practitioner’s approach Roger s. Pressman 6th edition McGraw-Hill

2.Software Engineering Somerville 7th edition

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Introduction to software Engineering

The Evolving role of software• Dual role of Software

A Product - Information transformer- producing, managing and displayingA Vehicle for delivering a product - Control of computer(operating system),the

communication of information(networks) and the creation of other programs

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• Software is defined as1. Instructions

- Programs that when executed provide desired function

2. Data structures -Enable the programs to adequately manipulate information 3. Documents -Describe the operation and use of the

programs.

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• Definition of Engineering -Application of science, tools and methods to find cost effective

solution to problems Definition of SOFTWARE ENGINEERING - SE is defined as systematic, disciplined and quantifiable

approach for the development, operation and maintenance of software

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Characteristics of software compared with hardware• Software is developed or engineered, it is not manufactured

in the classical sense.• Software does not wear out. However it deteriorates due to

change.• Software is custom built rather than assembling existing

components. -Although the industry is moving towards component based

construction, most software continues to be custom built

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CHARACTERISTICS OF HARDWARE

Failu

re ra

te

Time

“Infant mortality” “Wear out”

Fig: FAILURE CURVE FOR HARDWARE6

CHARACTERISTICS OF SOFTWARE

Fig: FAILURE CURVE FOR SOFTWARE

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THE CHANGING NATURE OF SOFTWARE

• Seven Broad Categories of software are challenges for software engineers

System software Application software Engineering and scientific software Embedded software Product-line software Web-applications Artificial intelligence software

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THE CHANGING NATURE OF SOFTWARE

• System software. System software is a collection of programs written to service other programs

• Embedded software -- resides in read-only memory --is used to control products and systems for the consumer and

industrial markets.

• Artificial intelligence software. Artificial intelligence (AI) software makes use of nonnumeric algorithms to solve complex problems that are not amenable to computation or straightforward analysis

• Engineering and scientific software. Engineering and scientific software have been characterized by "number crunching" algorithms.

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LEGACY SOFTWARE

• Legacy software are older programs that are developed decades ago– quality of legacy software is poor

• inextensible design , convoluted code• poor and nonexistent documentation,• test cases and results that are not achieved.

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Legacy systems evolve due to following reasons:The software must be adapted to meet the needs of new

computing environment or technology.The software must be enhanced to implement new

business requirements.The software must be extended to make it interoperable

with more modern systems or databaseThe software must be rearchitected to make it viable

within a network environment.

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Software Evolution

• Software evolves due to changes• Changes occur due to correction,adaption and enhancement• 8 Laws of unified theory

The Law of Continuing Change. The Law of Increasing Complexity. The Law of Self-Regulation The Law of Conservation of Organizational Stability. The Law of Conservation of Familiarity The Law of Continuing Growth The Law of Declining Quality The Feedback System Law

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• High rate of change of user requirements and environment on which software is working

• Large software• Cost• Scalability etc

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• An activity – strives to achieve a broad objective and– applied regardless of the application domain

and size of the project• An action

– encompasses a set of tasks that produce a major work product

– (e.g., architectural design)

• A task– focuses on a small, but well-defined objective

that produces a tangible outcome– (e.g., conducting a unit test

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SOFTWARE ENGINEERING-A LAYERED TECHNOLOGY

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SOFTWARE ENGINEERING-A LAYERED TECHNOLOGY

• Quality focus - Bedrock that supports software Engineering

eg :Total quality management, Six Sigma• Process

– Foundation for software Engineering– The software process forms the basis for management control

of software projects and – establishes the context in which technical methods are applied, – work products are produced, – milestones are established,– quality is ensured, and – change is properly managed.

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• Methods - Provide technical How-to’s for building software

– Methods encompass a broad array of tasks that include communication,

– requirements analysis, – design modeling,– program construction, – testing, and – support.

• Tools - Provide semi-automatic and automatic support for

process and methods

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A PROCESS FRAMEWORK

• Establishes the foundation for a complete software process• Identifies a number of framework activities applicable to all

software projects• Also include a set of umbrella activities that are applicable

across the entire software process.

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• Communication– Heavy Communication and collaboration with customer – Encompasses requirement gathering and other related

activity • Planning

– Establishes plan for software engineering work – It describe the technical task to be conducted – Risk that are likely to occur and the resource requirement– The work product to be produce and work schedule

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• Modeling – encompasses the creation of model that allow the developer

and customer to better understand software requirement– The deign that will achieve those requirement

• Construction– code generation – Testing required to un cover error in a code

• Deployment– The software is delivered to customer – Customers evaluate and give feedback based on evaluation

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process flow

• Describes how the framework activities and the actions and tasks that occur within each framework activity are organized with respect to sequence and time

– A linear process flow executes each of the five framework activities in sequence, beginning with communication and culminating with deployment

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• An iterative process flow repeats one or more of the activities before proceeding to the next

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• An evolutionary process flow executes the activities in a “circular”manner.

• Each circuit through the five activities leads to a more complete version of the software

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• A parallel process flow executes one or more activities in parallel with other activities (e.g., modeling for one aspect of the software might be executed in parallel with construction of another aspect of the software).

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• Software project tracking and control—– allows the software team to assess progress against the project plan – take any necessary action to maintain the schedule.

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• Risk management—– assesses risks that may affect the outcome of the

project or the quality of the product.• Steps

– Risk identification – Risk prioritization– Risk treatment

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• Software quality assurance—defines and conducts the activities required to ensure software quality.

• Technical reviews—assesses software engineering work products in an effort to uncover and remove errors before they are propagated to the next activity.

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• Measurement—– defines and collects process, project, and product

measures that assist the team in delivering software that meets stakeholders’ needs; can be used in conjunction with all other framework and umbrella activities.

• Software configuration management—– manages the effects of change throughout the

software process.

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• Reusability management—– defines criteria for work product reuse (including

software components) and establishes mechanisms to achieve reusable components.

• Work product preparation and production—– encompasses the activities required to create work

products such as models, documents, logs, forms,and lists.

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CAPABILITY MATURITY MODEL INTEGRATION (CMMI)

• Developed by SEI(Software Engineering institute)

• CMMI process meta model that defines the process characteristics that should exist if an organization wants to establish a software process that is complete

• CMMI can be represented in different ways1.A continuous model2.A staged model

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Focus of CMMI

SW-CMM is applied here

CMMI is applied here

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Bridging the Divide

CMMI:•Integrates systems and

software disciplines into one process improvement framework.

•Provides a framework for introducing new disciplines as needs arise.

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Staged Representation• Provides a proven sequence of improvements, each serving

as a foundation for the next• Permits comparisons across and among organizations by the

use of maturity levels

Indicates maturity of an organization’s standard process -- to answer

“What is a good order for approaching improvement across the organization?”

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Maturity Levels

• A maturity level is a well-defined evolutionary plateau of process improvement.

• There are five maturity levels.

• Each level is a layer in the foundation for continuous process improvement using a proven sequence of improvements, beginning with basic management practices and progressing through a predefined and proven path of successive levels.

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The Maturity Levels

1

2

3

4

5

Process unpredictable, poorly controlled, and reactive

Process characterized for projects and is often reactive

Process characterized for the organization and is proactive

Process measuredand controlled

Focus on continuous process improvement

Optimizing

QuantitativelyManaged

Defined

Initial

Managed

Optimizing

Defined

Continuous model:

• Lets organization select specific improvement that best meet its business objectives and minimize risk

• Levels are called capability levels.• Describes a process in 2 dimensions• Each process area is assessed against specific goals

and practices and is rated according to the following capability levels.

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Continuous Representation• Allows you to select the order of improvement that best meets

your organization’s business objectives and mitigates your organization’s areas of risk

• Enables comparisons across and among organizations on a process-area-by-process-area basis

• Provides an easy migration from other models with a continuous representation to CMMI

Indicates improvement within a single process area -- to answer,

“What is a good order for approaching improvement of this process area?”

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Capability Levels• A capability level is a well-defined evolutionary plateau

describing the organization’s capability relative to a process area.

• There are six capability levels.• For capability levels 1-5, there is an associated generic

goal.• Each level is a layer in the foundation for continuous

process improvement.• Thus, capability levels are cumulative, i.e., a higher

capability level includes the attributes of the lower levels.

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The Capability Levels

5 Optimizing

4 Quantitatively Managed

3 Defined

2 Managed

1 Performed

0 Incomplete

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Model Components• Process Areas (PA)

– Specific Goals (SG) Required• Specific Practices (SP) Expected

– Typical Work Products Informative– Sub-practices Informative– Notes Informative– Discipline Amplifications Informative– References Informative

– Generic Goals (GG) Required• Generic Practices (GP) Expected

– Generic Practice Elaborations Informative

Specific Practices (CL1 - “Base Practices”)

SP1.1-1:Estimate the Scope of the Project

SP1.2-1:Establish Estimates of Work Product and Task Attributes

SP1.3-1:Define Project Life CycleSP1.4-1:Determine Estimates of

Effort and CostSP2.1-1:Establish Budget and

ScheduleSP2.2-1:Identify Project RisksSP2.3-1:Plan for Data ManagementSP2.4-1:Plan for Project ResourcesSP2.5-1:Plan for Needed Knowledge

and SkillsSP2.6-1:Plan Stakeholder

Involvement

PP - Capability Level 1Project Planning

Generic Practices (CL1))

GP1.1: Perform Base Practices

If all of the base practices are performed,

Then, the associated Specific Goals and Generic Goal 1 are satisfied,

So, the Process Area is rated at Capability Level 1 (CL1) - Performed.

SP2.7-1:Establish the Project PlanSP3.1-1:Review Plans that Affect the

ProjectSP3.2-1:Reconcile Work and Resource

LevelsSP3.3-1:Obtain Plan Commitment

CMMI

• INCOMPLETE -Process is adhoc.Objective and goal of process areas are not

known

• Performed -Goal,objective,work tasks,work products and other activities of

software process are carried out

• Managed -Activities are monitored, reviewed, evaluated and controlled

• Defined -Activities are standardized, integrated and documented

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• Quantitatively Managed -Metrics and indicators are available to measure the process

and quality - Defect Prevention

• Optimized - Continuous process improvement based on quantitative feed

back from the user -Use of innovative ideas and techniques, statistical quality

control and other methods for process improvement.

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Maturity levelsLEVEL FOCUS PROCESS AREAOptimizing Continuous process

Improvement-Organizational Innovation and Deployment -Causal Analysis and Resolution

Quantitatively managed

Quantitative management

-Organizational process performance-Quantitative project management

Defined Process standardized Requirements Development Technical Solution Product IntegrationVerification Validation Organizational Process Focus Organizational Process Definition Organizational Training Integrated Project Management Risk Management 55

−Integrated Teaming−Integrated Supplier Management−Decision Analysis and Resolution−Organizational Environment for Integration

Managed Basic project management Requirements ManagementProject Planning Project Monitoring and Control Supplier Agreement Measurement and Analysis Process and Product Quality Assurance Configuration Management

Performed

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SW-CMM V1.1 vs. CMMI V1.1

Defect Prevention Causal Analysis and ResolutionTechnology Change Mgmt Organizational Innovation & DeploymentProcess Change Management

Quantitative Process Mgmt Organizational Process PerformanceSoftware Quality Mgmt Quantitative Project Management

Organization Process Focus Organization Process Focus Organization Process Definition Organization Process DefinitionTraining Program Organizational TrainingIntegrated Software Mgmt Integrated Project Management

Risk ManagementSoftware Product Engr Requirements Development

Technical SolutionProduct Integration

Intergroup Coordination VerificationPeer Reviews Validation

Decision Analysis and Resolution

Requirements Management Requirements ManagementSoftware Project Planning Project PlanningSoftware Project Tracking & Oversight Project Monitoring and ControlSoftware Subcontract Mgmt Supplier Agreement ManagementSoftware Quality Assurance Product & Process Quality Assurance Software Configuration Mgmt Configuration Management

Measurement and Analysis

LEVEL 5OPTIMIZING

LEVEL 4MANAGED

LEVEL 3DEFINED

LEVEL 2REPEATABLE

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Key Process Areas (KPAs)

Process Areas (PAs)

PROCESS ASSESSMENT

• Does not specify the quality of the software or whether the software will be delivered on time or will it stand up to the user requirements.

• It attempts to keep a check on the current state of the software process with the intention of improving it.

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PROCESS ASSESSMENT

Software Process

Software ProcessAssessment

Software Process improvement

Capability determinationMotivates

Lead

s to

Leads to

Identi

fies

Modific

ation

to

Identi

fies

Capabilities & Risk

Examined

by

APPROACHES TO SOFTWRE ASSESSMENT

• Standard CMMI assessment (SCAMPI)• CMM based appraisal for internal process improvement• SPICE(ISO/IEC 15504)• ISO 9001:2000 for software

• Refer PROCESS ASSESSMENT.ppt• ProcessAssessmentMethod.ppt• process_assmnt.docx

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Personal and Team Software Process

• Personal software process PLANNING HIGH LEVEL DESIGN HIGH LEVEL DESIGN REVIEW DEVELOPMENT POSTMORTEM

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Personal and Team Software Process

• Team software process Goal of TSP- Build self-directed teams- Motivate the teams - Acceptance of CMM level 5 behavior as normal to accelerate

software process improvement- Provide improvement guidance to high maturity organization- Refer psp.doc- psp.docx

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CLASSICAL WATERFALL MODEL

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Communication Planning

ModelingConstruction

Deployment analysis design code

test

project initiation requirement gathering estimating

scheduling tracking

delivery support feedback

By Royce:

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Sl no

advantages disadvantages When to use

1 It allows for departmentalization and managerial control.

it assumes that no development error is ever committed by the engineers during any of the life cycle phases. However, in practical development environments, the engineers do commit a large number of errors in almost every phase of the life cycle

Requirements are well understood

2 Simple and easy to understand and use

It is difficult for customer to state all requirements explicitly(without any change)

Automation of existing manual system

3 Phases are processed and completed one at a time.

Working version of software will not be available until late in project span

Short duration project

4 Works well for smaller projects where requirements are very well understood.

User feedback not encouragedNot a good model for complex and object-oriented projects.

5 A schedule can be set with deadlines for each stage of development and a product can proceed through the development process like a car in a car-wash, and theoretically, be delivered on time.

. Once a defect is detected, the engineers need to go back to the phase where the defect had occurred and redo some of the work done during that phase and the subsequent phases to correct the defect and its effect on the later phases

• Incremental Process Models• The Incremental Model• The RAD Model

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5

Sl no advantages disadvantages When to use

1 Generates working software quickly and early during the software life cycle.

Needs good planning and design.

when the requirements of the complete system are clearly defined and understood.

2 Lowers initial delivery cost.

Total cost is higher than waterfall.

A new technology is being used

3 Easier to manage risk because risky pieces are identified and handled during individual iteration.

Needs a clear and complete definition of the whole system before it can be broken down and built incrementally.

Staffing is not available for complete implementation of project

4 It is easier to test and debug during a smaller iteration.In this model customer can respond to each built.

There are some high risk features and goals.

5 This model is more flexible – less costly to change scope and requirements.

http://istqbexamcertification.com/what-is-waterfall-model-advantages-disadvantages-and-when-to-use-it/

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Communication

Planning

Modelingbusiness modeling data modeling process modeling

Constructioncomponent reuse automatic code generation testing

Deployment

60 - 90 days

Team # 1


Constructioncomponent reuse automatic code generat ion test ing


Const ruct ioncomponent reuse automatic code generation testing

Team # 2

Team # n

integration delivery feedback

RAD

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Sl advantages disadvantages When to use

1 Progress can be measured.Iteration time can be short with use of powerful RAD tools.

Dependency on technically strong team members for identifying business requirements.

Sufficient human recourse is needed to create right no of RAD team

Suitable for project requiring shorter development times.

2 Integration from very beginning solves a lot of integration issues.

Only system that can be modularized can be built using RAD.

Sufficient human recourse is needed to create right no of RAD team

Requirements are understood and project scope is constrained

3 Encourages customer feedback, Changing requirements can be accommodated.

Requires highly skilled developers/designers.High dependency on modeling skills.

Performances issue

Fully functional system is to be delivered in short span of time

4 Reduced development time.Increases reusability of components

Management complexity is more.Suitable for systems that are component based and scalable

For large, but scalable projects, RAD requires sufficient human resources to create the right number of RAD teams.

5 Productivity with fewer people in short time. Requires user involvement throughout the life cycle.

Inapplicable to cheaper projects as cost of modeling and automated code generation is very high

• Evolutionary Process Model• Prototype• Spiral model

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Prototype

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Prototype

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Communication

Quick plan

Construction of prototype

Modeling Quick design

Delivery & Feedback

Deployment

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1 Provides a working model to the user early in the process, enabling early assessment and increasing user's confidence.

If the user is not satisfied by the developed prototype, then a new prototype is developed. This process goes on until a perfect prototype is developed. Thus, this model is time consuming and expensive.

User requirements are not complete

2 serves to clarify requirements, which are not clear, hence reducing ambiguity and improving communication between the developers and users.

The developer loses focus of the real purpose of prototype and hence, may compromise with the quality of the software. For example, developers may use some inefficient algorithms while developing the prototype.

Technical issues are not clear

3 Helps in reducing risks associated with the software.

Prototyping can lead to false expectations “customer sees what appears to be a working version of the Software”.

4 User feedback not encouraged The primary goal of prototyping is speedy development, thus, the system design can suffer as it is developed in series without considering integration of all other components

5 The developer gains experience and insight by developing a prototype there by resulting in better implementation of requirements.

Spiral model:Invented by Dr. Barry Boehm

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communication

planning

modeling

constructiondeployment delivery feedback

start

analysis design

code test

estimation scheduling risk analysis

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1 Avoids the problems resulting in risk-driven approach in the softwareRe-evaluation after each step allows changes in user perspectives, technology advances, or financial perspectives.

Assessment of project risks and its resolution is not an easy task.

Spiral may go indefinitely

End of project may not be known early

suitable for development of technically challenging software products that are prone to several kinds of risks

2 Specifies a mechanism for software quality assurance activities

Difficult to estimate budget and schedule in the beginning as some of the analysis is not done until the design of the software is developed.

Projects build on untested assumptions

3 Development can be divided into smaller parts and more risky parts can be developed earlier which helps better risk management

It demands considerable risk assessment expertise and relies on this expertise for success

Is utilized by complex and dynamic projects

4 Allows for extensive use of prototypes

If risks is not uncovered and managed problems will surely occur

5 Estimation of budget and schedule gets realistic as the work progresses.

Large number of intermediate stages requires excessive documentation.

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Under review

Baselined

Done

Underrevision

Awaitingchanges

Underdevelopment

none

Modeling activity

represents the stateof a software engineeringactivity or task