ProcessModels

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B. Computer Sci. (SE) (Hons.)

CSEB233: Fundamentals

of Software Engineering

ProcessModels


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Lesson Objectives

Describe the types of process flows

Determine task set for software process activities

Explain software process patterns

Discuss several process assessment and improve-ment frameworks

Analyze prescriptive and specialized software

process models Select a process model for software development

project


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A Generic Process Model

A software process:

o a collection of work activities, actions, tasks, which

are performed when software is to be created.

A process (model or framework )

o is where these activities, actions, and tasks reside,

and that defines their relationship with the process

and with one another.oAlso known as an abstract representation of a

software process.


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A Generic Process Model

Shows the technical work hierarchy

o activities encompassing (including)

actions, populated by tasks.

Each action is defined by a set of

tasks that defines:

o the actual workto complete

o

the work productsto produceo the quality assurance filters to apply, and

o the milestonesthat are used to indicate the

project and product progress


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Process Activities

Framework & Umbrella

Framework activities :o generic activities that are applicable to all software projects, regardless

of their size or complexity

o Include communication; planning; modeling, construction; anddeployment

A process framework involves heavy communication with the customer togather requirements;

this activity establishes a plan for the software engineering work that follows.

It involves creation of models that will assist the developer and the customerto understand the requirements and design them;

it thereby involves construction (code generation and error testing).

It finally provides feedback based on the evaluation.


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Process Activities

Framework & Umbrella

Umbrella activities:o complementary activities applied throughout a software project and help manage

and control progress, quality, change, and risk.

o Include:

Software Project Tracking and Control (Assess progress and take action to maintain commitment)

Risk Management (Assess risks that will affect outcome and quality)

Software Quality Assurance (Define and conduct activities to ensure software quality)

Formal Technical Reviews (Assess Work products to uncover and rectify defects)

Measurement (Define and collect process, project and product metrics)

Software Configuration Management (Manage effect of change)

Reusability Management (Define criteria and establish mechanisms for reuse)

Work Product (Activities required to create the work products)


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Process Models

ProcessFlows


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Process Flow

Describes how the framework activities and the actions and tasks that

occur within each activity are organized with respect to sequence

and time.

The flows:

o Linear: execute the framework activities in sequence.

o Iterative: repeats one or more of the activities before proceeding to the next.

o Evolutionary: execute the activities in a circularmanner.

o Parallel: executes one or more activities with other activities in the same time.


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Process Flow


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Process Models

TaskSet


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Identifying a Task Set

A task set defines the actual work to be done to

accomplish the objectives of a software

engineering action

oA list of the tasks to be accomplished

oA list of the work products to be produced

oA list of the quality assurance filters to be applied


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Key Questions in Determining Task Set

Q: What actions are appropriate for aFramework activity, given:

o the nature of the problem to be solved;

o the characteristics of the people doing the work;

and

o the stakeholders of the project?

Q: What work tasks (task set) that these

actionsshould encompass?

Different projects require different task sets

o The tasks should be selected based on problems

and project characteristics.


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Example

Nature of the problems and project :o A small software project requested by one person (at a

remote location) with simple, straightforward requirements.

Actions (x):o Communication action: develop requirements

Task set:

o Make contact with stakeholder via telephone.o Discuss requirements and take notes.

o Organize notes into a brief written statement of requirements.

o E-mail to stakeholder for review and approval.


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Example

1. Customer communication (a processactivity).

2. Analysis (an action).

3. Requirements gathering (a process task).

4. Reviewing a work product (a process task).

5. Design model (a work product).


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Process Models

ProcessPatterns


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Process Patterns

A process patterno describes a related process to problem that is

encountered or happened during software engineeringwork,

o identifies the environmentin which the problem has beenencountered, and

o suggests one or more proven solutions to the problem

In more general terms, a process pattern provides atemplateo a consistent method for describing problem solutions

within the context of the software process


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Process Pattern Types

Task patternso defines a problem with a software engineering

action or work task and relevant to successful softwareengineering practice.

Stage patternso defines a problem with a framework activity for

the process

Phase patternso define the sequence of framework activities that occur

with the process, even when the overall flow of activities isiterative in nature


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Process Models

ProcessAssessment&

Improvement


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Process Assessment and

Improvement: Approaches

Standard CMMI Assessment Method forProcess Improvement (SCAMPI):o A standard Used to identify strengths,

weaknesses, and ratings relative to SEICMMI appraisal reference model, which isapplicable to internal process improvement

and external capability determination CMM-Based Appraisal for Internal Process

Improvement (CBA IPI):o A standard provides a diagnostic technique

for assessing the relative maturity of asoftware organization; uses the SEI CMM asthe basis for the assessment [Dun01].

o However, CMM has been retired by SEI sincethe introduction of CMMI group of standards

Capability Maturity Model Integration (CMMI)

Software Engineering Institutes (SEI)


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Process Assessment and

Improvement: Approaches

SPICE (ISO/IEC15504):

o Standardthat defines a set of requirements for software process assessment.

o The intent of the standard is to assist organizations in developing an objective

evaluation of the efficacy of any defined software process [ISO08]

ISO 9001:2000 for Software:

o A generic standard that applies to any organization that wants to improve the

overall quality of the products, systems, or services that it provides.

o Therefore, the standard is directly applicable to software organizations and

companies [Ant06]

Software Process Improvement and Capability Determination (SPICE)

International Organization for Standardization (ISO)International Electrotechnical Commission (IEC)


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Tut

In Group of 5 persons; Explain the difference

between Activity, Action, and Task. Provide

example for each of them.


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Process Models

Prescriptive&Specialized

ProcessModels


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Prescriptive Process Models

Defines a distinct set of activities, actions, tasks,milestones, and work products that are requiredto engineer high-quality software.

The activities may be linear, incremental, or

evolutionary.


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Waterfall Modelo represents elements of a linear process flow

V

Incremental Model

o combines elements of linear and parallel process flows Evolutionary Model

o follows the evolutionary process flow that combines elementsof linear and iterative process flows

Prototyping

Spiral

Concurrent Modelo combines elements of iterative and parallel process flows


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The Waterfall Model

Represents a linear process flow from communica-tion through deploymentoAlso known as the classic SDLC

The original Waterfall model proposed by WinstonRoyce in 1970 made provision for feedback loopso but many organizations apply this model as if it were

strictly linear

Communication

Planning

Modeling

ConstructionDeployment

analysis

designcode

test

project initiation

requirement gathering estimating

scheduling

tracking

delivery

support

feedback


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An Analysis of Waterfall Model

Characteristics Strengths Weaknesses Applicability

It suggests a

systematic, sequential

approach to SE,

starting from

requirements

specification throughplanning, modeling,

construction, testing,

deployment and

support of the

completed system.

Each major activity is

marked by milestonesand deliverables (i.e.

documents).

Simple and easy to

use/explain to

customers.

The staged

development cycleenforces discipline:

every phase has a

defined start and end

point, and progress

can be conclusively

identified (through

the use of

milestones)

Real projects rarely follow the

linear flow that the model

proposes. Although iteration is

indirectly allowed, changes are

costly, involve significant rework

and can cause confusiontoproject team.

The model requires the customer

to state all requirements

explicitly, which is often very

difficult to achieve.

The working softwarewill not be

available until late in the project,

which can be disastrous for late

discovery of major defects.

Leads to blocking states in

which some project team members

must wait for others to complete

dependent tasks.

When requirements are

well understood and

unlikely to change

radically during system

development (e.g., in a

well-defined enhancementto an existing system).

When software

development

technologies and tools

are well known.

The work tasks in the

project are to proceed to

completion in a linear

manner.


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The V-Model

Variation in representing

the Waterfall model

Illustrates how V&V

actions are associatedwith earlier SE action

There is no fundamental

difference between the

Waterfall model and the

V-model


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The Incremental Model

Rather than deliver the software product as a singledelivery, the development and delivery is broken downinto incrementswith each increment delivering part of therequired functionality.

User requirements are prioritised and the highest priorityrequirements are included in early increments.

Once the development of an increment is started, therequirements are frozen but requirements for laterincrementscan continue to evolve


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The Incremental Modelalittlemoreisaddedeachtime

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

analys is

design code

t e s t

increment # 1

increment # 2

delivery of

1st increment

delivery of

2nd increment

delivery of

nt h increment

increment # n

project calendar time


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

analys is

design code

t e s 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

analys is

designcode

t e s t


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After the first increment, a core product is

delivered, which can already be used by the

customer.

Based on customer feedback, a plan is

developed for the next increments, andmodifications are made accordingly.

This process continues, with increments being

delivered until the complete product is

delivered.

Word-processing software developed using the incremental paradigm might deliver

Basic file management,

Editing and document production capabilities in the second increment; Spelling and grammar checking in the third increment; and

Advanced page layout capability in the fourth increment.

It should be noted that the process flow for any increment can incorporate the

prototyping paradigm.

For example?


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The Evolutionary Model: Prototyping

Software prototyping: incomplete versions of the softwareprogram being developed.

Using this process model, a prototype - an early approximation of a finalsoftware product - is built, tested, and then reworked as necessaryo until an acceptable prototype is finally achieved from which the complete

software product is developed

Although it can be implemented as a stand-alone process model, it ismore commonly used as part of other process models

The main purpose of the model is to help better understand what it is tobuilt when requirements are fuzzy and get valuable feedback from theusers early in the project


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The Evolutionary Model: Prototyping

Communication

Quick plan

Construction

of

prototype

Model ing

Quick design

Delivery

& Feedback

Deployment

communication

Quickplan

ModelingQuick design

Constructionof prototype

Deploymentdelivery &feedback

If the prototype was working properly;

???


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The Evolutionary Model: Spiral

A process model that combines the iterative nature of

prototypingwith the systematic aspects of waterfall model.

The spiral model can be thought of as a repeating waterfall model

that emphasizes risk assessment and that is executed in an

incremental fashion.

Each loop/pass through the spiral model consists of risk

assessment and other framework activities from communication

through deployment


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communication

planning

modeling

constructiondeployment

delivery

feedback

start

analysis

design

code

test

estimation

scheduling

risk analysis

Used when requirements are not well understood and risks are high


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Used when requirements are not well understood and risks are high


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The Concurrent Model

A process model that combines the iterative and

parallel elements of any of the prescriptive

process models.

In this model, all SE activities (framework or

umbrella) exist concurrently but assess in

different states


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The Concurrent Model

Under review

Baselined

Done

Under

revision

A wait ing

changes

Under

development

none

Modeling act ivity

represents the state

of a software engineering

activity or task

For exampleearly in a project the customer

communication activity has completed its

first iteration and exists in the awaiting

changes state. The analysis activity

(which existed in the none state while

initial customer communication wascompleted) now makes a transition into

the under development state. If, however,

the customer indicates that changes in

requirements must be made, the analysis

activity moves from the under

development state into the awaitingchanges state.

The concurrent process model defines a

series of events that will trigger

transitions from state to state for each of

the software engineering activities.


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Specialized Process Models

Specialized Process Models is a combination of both component

based development model (CBD) and formal method model.

Special process models take on many of the characteristics of

one or more of the conventional models.

Specialized models tend to be applied when a narrowly defined

software engineering approach is chosen.


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Component based software development (CBSD)o the process to apply when reuse is a development objective

Formal methodso emphasizes the mathematical specification of requirements,

which can demonstrate software correctness but are notwidely used.

Aspect-oriented software development (AOSD)o provides a process and methodological approach for defining,

specifying, designing, and constructing aspects

Unified Processo a use-case driven, architecture-centric, iterative and

incrementalsoftware process closely aligned with the UnifiedModeling Language (UML)


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Agile Processo An iterative approach to requirements specification, construction

and deployment, which support rapid changes to requirements

Personal Process Modelo Emphasizes the need to record and analyze errors made by each

individual, so that he/she can develop a strategy to eliminate them

Team Process Modelo Build self-directed teams that plan and track their work, establish

goals, and own their processes and plans. These can be puresoftware teams or integrated product teams (IPT) of three to about

20 engineerso Show managers how to coach and motivate their teams and how to

help them sustain peak performance


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Process Models

SelectingaProcessModel


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Selecting a Process Model

Factors to Consider

The characteristics of the problems to be solvedo Such as complexity of the problem, etc.

o e.g. simple with clear, stable requirements, or complex withchanging, unstable requirements, etc.

The characteristics of the projecto Such as the customers who have requested the product and the

people who will do the work, etc.

o e.g. Uncertain requirements, breakthrough technology

The characteristics of the producto

Such as quality attributes or metric of the product, product domain,etc.

The project environment in which the software team workso Such as political, cultural, language, etc.


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Summary

There are four types of process flows linear, iterative,evolutionary, and parallel.

Software process patterns may suggest one or moreproven solutions to the problem from other projects, which

can be reused in another project There are several process assessment and improvements

frameworks that can be exercised by practitioners

The analyses of prescriptive and specialized softwareprocess models would help select the most appropriateprocess model for a software development project, whichcan be proceeded with the identification of task set for theproject


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An Exercise

The Project:o Assume that you are in charge of a project to create a portal

for Selangor.

o This portal would include a homepage with links to a widerange of discounted travel packages to major destinations inSelangor, links to certain featured places like golf courses,shopping complexes and places to eat, links to the detailedmap of Selangor, and links to news and events listing

o It also includes a bulletin board and chat room feature wheretourists (international and local tourists) can exchange

information.o The portal should also provide Automated Teller Machine

(ATM) locator, time zone converter, and currency converter.


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An Exercise

Select a software process model that you would

recommend to be implemented in the above

mentioned project

Why is the software process model selected?


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THE ENDDr.AbdallahAbualkishik

CollegeofInformationTechnology

ProcessModels

Documents

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