process models- software engineering

SRIKRISHNAARTSANDSCIENCECOLLEGE
SOFTWARE ENGINEERING
PROJECT ON :
PROCESS MODELS
Submitted By :Arun.P

SoftwareProcess
• A framework for the activities, actions, and
tasks that are required to build high-quality
software.
• SP defines the approach that is taken as
software is engineered.
• Is not equal to software engineering, which
also encompasses technologies that
populate the process– technical methods
and automated tools.

A ProcessGenericModel
As we discussed before, a generic process
framework for software engineering defines
five framework activities-communication,
planning, modeling, construction, and
deployment.

In addition, a set of umbrella activities-
project tracking and control, risk
management, quality assurance,
configuration management, technical
reviews, and others are applied throughout
the process.

Processflow
Linear process flow executes each of the five
activities in sequence.
An iterative process flow repeats one or
more of the activities before proceeding to
the next.

An evolutionary process flow executes the
activities in a circular manner. Each circuit
leads to a more complete version of the
software.
 A parallel process flow executes one or
more activities in parallel with other
activities ( modeling for one aspect of the
software in parallel with construction of
another aspect of the software.

Identifyinga Task Set
Before you can proceed with the process
model, a key question: what actions are
appropriate for a framework activity given
the nature of the problem, the
characteristics of the people and the
stakeholders?
A task set defines the actual work to be done
to accomplish the objectives of a software
engineering action.
A list of the task to be accomplished
A list of the work products to be
produced
A list of the quality assurance filters to
be applied.

For example, a small software project
requested by one person with simple
requirements, the communication activity
might encompass little more than a phone
all with the stakeholder. Therefore, the only
necessary action is phone conversation, the
work tasks of this action are:
1. Make contact with stakeholder via
telephone.
2. Discuss requirements and take notes.
3. Organize notes into a brief written
statement of requirements.
4. E-mail to stakeholder for review and
approval.
Example for identifying a task:

The task sets for Requirements gathering
action for a simple project may include:
1.Make a list of stakeholders for the
project.
2. Invite all stakeholders to an informal
meeting.
3. Ask each stakeholder to make a list
of features and functions required.
4. Discuss requirements and build a
final list.
5.Prioritize requirements.
6. Note areas of uncertainty.

SoftwareProcessModelDescription:
• A software process model is an abstract
representation of a process. It presents a
description of a process.
• When we describe and discuss processes, we
usually talk about the activities in these
processes such as specifying a data model,
designing a user interface, etc. and the
ordering of these activities.
• Process descriptions may also include:
– Products, which are the outcomes of a
process activity;
– Roles, which reflect the responsibilities
of the people involved in the process;
– Pre- and post-conditions, which are
statements that are true before and after
a process activity has been enacted or a
product produced.
– Notation: activities, products

The WaterFallModel
l Requirements analysis and definition
l System and software design
l Implementation and unit testing
l Integration and system testing
l Operation and maintenance
The main drawback of the waterfall model is the
difficulty of accommodating change after the

process is underway. One phase has to be
complete before moving onto the next phase
Waterfallmodelproblems:
Inflexible partitioning of the project into
distinct stages makes it difficult to respond
to changing customer requirements.
Therefore, this model is only appropriate
when the requirements are well-understood
and changes will be fairly limited during the
design process.
Few business systems have stable
requirements.
The waterfall model is mostly used for large
systems engineering projects where a
system is developed at several sites.
The IncrementalModel

• When initial requirements are reasonably
well defined, but the overall scope of the
development effort precludes a purely linear
process. A compelling need to expand a
limited set of new functions to a later
system release.

• It combines elements of linear and parallel
process flows. Each linear sequence
produces deliverable increments of the
software.
• The first increment is often a core product
with many supplementary features. Users
use it and evaluate it with more
modifications to better meet the needs.
V-Model

A variation of waterfall model depicts the
relationship of quality assurance actions to the
actions associated with communication,
modeling and early code construction activates.
Team first moves down the left side of the V to
refine the problem requirements. Once code is
generated, the team moves up the right side of

the V, performing a series of tests that validate
each of the models created as the team moved
down the left side.

Evolutionary Models:
Prototyping:
• When to use: Customer defines a set of
general objectives but does not identify
detailed requirements for functions and
features. Or Developer may be unsure of the
efficiency of an algorithm, the form that
human computer interaction should take.
• What step: Begins with communication by
meeting with stakeholders to define the
objective, identify whatever requirements
are known, outline areas where further
definition is mandatory. A quick plan for
prototyping and modeling (quick design)
occur. Quick design focuses on a
representation of those aspects the software
that will be visible to end users. ( interface
and output). Design leads to the
construction of a prototype which will be

deployed and evaluated. Stakeholder’s
comments will be used to refine
requirements.
• Both stakeholders and software engineers
like the prototyping paradigm. Users get a
feel for the actual system, and developers
get to build something immediately.
However, engineers may make
compromises in order to get a prototype
working quickly. The less-than-ideal choice
may be adopted forever after you get used to
it.

2) Spiral
• It couples the iterative nature of prototyping
with the controlled and systematic aspects
of the waterfall model and is a risk-driven
process model generator that is used to

guide multi-stakeholder concurrent
engineering of software intensive systems.
• Two main distinguishing features: one is
cyclic approach for incrementally growing a
system’s degree of definition and
implementation while decreasing its degree
of risk. The other is a set of anchor point
milestones for ensuring stakeholder
commitment to feasible and mutually
satisfactory system solutions.

• A series of evolutionary releases are
delivered. During the early iterations, the
release might be a model or prototype.
During later iterations, increasingly more
complete version of the engineered system
are produced.
• The first circuit in the clockwise direction
might result in the product specification;
subsequent passes around the spiral might
be used to develop a prototype and then
progressively more sophisticated versions of
the software. Each pass results in
adjustments to the project plan. Cost and
schedule are adjusted based on feedback.
Also, the number of iterations will be
adjusted by project manager.
• Good to develop large-scale system as
software evolves as the process progresses
and risk should be understood and properly
reacted to. Prototyping is used to reduce
risk.

• However, it may be difficult to convince
customers that it is controllable as it
demands considerable risk assessment
expertise.
StillOtherProcessModels
• Component based development—the
process to apply when reuse is a
development objective ( like spiral model)

• Formal methods—emphasizes the
mathematical specification of requirements
( easy to discover and eliminate ambiguity,
incompleteness and inconsistency)
• Aspect Oriented software development
(AOSD)—provides a process and
methodological approach for defining,
specifying, designing, and constructing
aspects
• Unified Process—a “use-case driven,
architecture-centric, iterative and
incremental” software process closely
aligned with the Unified Modeling Language
(UML) to model and develop object-
oriented system iteratively and
incrementally.
The Unified Process (UP):

UP Work Products:
Personal Software Process:
• Planning. This activity isolates
requirements and develops both size and
resource estimates. In addition, a defect
estimate (the number of defects projected
for the work) is made. All metrics are
recorded on worksheets or templates.

Finally, development tasks are identified
and a project schedule is created.
• High-level design. External
specifications for each component to be
constructed are developed and a component
design is created. Prototypes are built when
uncertainty exists. All issues are recorded
and tracked.
• High-level design review. Formal
verification methods (Chapter 21) are
applied to uncover errors in the design.
Metrics are maintained for all important
tasks and work results.
• Development. The component level
design is refined and reviewed. Code is
generated, reviewed, compiled, and tested.
Metrics are maintained for all important
tasks and work results.
• Postmortem. Using the measures and
metrics collected (this is a substantial
amount of data that should be analyzed

statistically), the effectiveness of the process
is determined. Measures and metrics should
provide guidance for modifying the process
to improve its effectiveness.
Team Software Process (TSP):
Build self-directed teams that plan and
track their work, establish goals, and own
their processes and plans. These can be pure
software teams or integrated product teams
(IPT) of three to about 20 engineers.
Show managers how to coach and motivate
their teams and how to help them sustain
peak performance.
Accelerate software process improvement
by making CMM Level 5 behavior normal
and expected.
 The Capability Maturity Model (CMM),
a measure of the effectiveness of a

software process, is discussed in Chapter
30.
Provide improvement guidance to high-
maturity organizations.
Facilitate university teaching of industrial-
grade team skills.

process models- software engineering

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