IIIT Dharwad Dept.

of DSIS

Software Engineering (DS 203)

Dr. Manjunath K Vanahalli

Department of Data Science and Artifical Intelligence
Indian Institute of Information Technology Dharwad, India

February 6, 2023

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Evolutionary Process Models

Software, like all complex systems, evolves over a period of time. Busi-
ness and product requirements often change as development proceeds,
making a straight line path to an end product unrealistic

Tight market deadlines make completion of a comprehensive software

product impossible, but a limited version must be introduced to meet
competitive or business pressure

A set of core product or system requirements is well understood, but

the details of product or system extensions have yet to be defined.

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Evolutionary Process Models

In these and similar situations, you need a process model that has been
explicitly designed to accommodate a product that grows and changes.

Evolutionary models are iterative. They are characterized in a manner

that enables you to develop increasingly more complete versions of the
software

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Evolutionary Process Models

Two common evolutionary process models.

Prototyping Model

The Spiral Model

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Prototyping

Often, a customer defines a set of general objectives for software, but

does not identify detailed requirements for functions and features.

In other cases, the developer may be unsure of the efficiency of an

algorithm, the adaptability of an operating system, or the form that
human-machine interaction should take.

In these, and many other situations, a prototyping paradigm may offer

the best approach.

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The Prototyping model

Figure 1. The Prototyping model

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Prototyping

You meet with other stakeholders to define the overall objectives for
the software, identify whatever requirements are known, and outline
areas where further definition is mandatory.

A prototyping iteration is planned quickly, and modeling (in the form

of a “quick design”) occurs.

A quick design focuses on a representation of those aspects of the

software that will be visible to end users (e.g., human interface layout
or output display formats).

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Prototyping

The quick design leads to the construction of a prototype. The proto-

type is deployed and evaluated by stakeholders, who provide feedback
that is used to further refine requirements.

Iteration occurs as the prototype is tuned to satisfy the needs of various

stakeholders, while at the same time enabling you to better understand
what needs to be done.

Both stakeholders and software engineers like the prototyping paradigm.

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Prototyping

Users get a feel for the actual system, and developers get to build
something immediately. Yet, prototyping can be problematic for the
following reasons:

Stakeholders see what appears to be a working version of the software,

unaware that the prototype is held together haphazardly, unaware that
in the rush to get it working you haven’t considered overall software
quality or long-term maintainability.

An inefficient algorithm may be implemented simply to demonstrate ca-

pability. After a time, you may become comfortable with these choices
and forget all the reasons why they were inappropriate. The less-than-
ideal choice has now become an integral part of the system.

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The Spiral Model

The spiral model is an evolutionary software process model that couples

the iterative nature of prototyping with the controlled and systematic
aspects of the waterfall model.

It provides the potential for rapid development of increasingly more

complete versions of the software.

The spiral development model is a risk -driven process model generator

that is used to guide multi-stakeholder concurrent engineering of soft-
ware intensive systems.

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The Spiral Model

The spiral model is an evolutionary software process model that couples

the iterative nature of prototyping with the controlled and systematic
aspects of the waterfall model.

It has two main distinguishing features. One is a cyclic approach for

incrementally growing a system’s degree of definition and implementa-
tion 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.

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The Spiral model

Figure 2. The Spiral model

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The Spiral Model

Using the spiral model, software is developed in a series of evolution-

ary releases. During early iterations, the release might be a model or
prototype.

During later iterations, increasingly more complete versions of the en-

gineered system are produced.

A spiral model is divided into a set of framework activities defined by

the software engineering team

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The Spiral Model

Each of the framework activities represent one segment of the spiral

path illustrated in Figure

As this evolutionary process begins, the software team performs ac-

tivities that are implied by a circuit around the spiral in a clockwise
direction, beginning at the center

The first circuit around the spiral might result in the development of
a product specification; subsequent passes around the spiral might be
used to develop a prototype and then progressively more sophisticated
versions of the software.

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The Spiral Model

Each pass through the planning region results in adjustments to the

project plan.

Cost and schedule are adjusted based on feedback derived from the
customer after delivery

The project manager adjusts the planned number of iterations required

to complete the software.

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AGILE Development

What is Agile Development?

Agile software engineering combines a philosophy and a set of devel-

opment guidelines.

The philosophy encourages customer satisfaction and early incremen-

tal delivery of software; small, highly motivated project teams; informal
methods; minimal software engineering work products; and overall de-
velopment simplicity.

The development guidelines stress delivery over analysis and design (al-
though these activities are not discouraged), and active and continuous
communication between developers and customers.

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AGILE Development

Who does it

Software engineers and other project stakeholders (managers, customers,

end users) work together on an agile team—a team that is self-organizing
and in control of its own destiny.

An agile team fosters communication and collaboration among all who

serve on it.

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AGILE Development

Why is it important

The modern business environment that spawns computer-based sys-

tems and software products is fast-paced and ever-changing.

Agile software engineering represents a reasonable alternative to con-

ventional software engineering for certain classes of software and certain
types of software projects.

It has been demonstrated to deliver successful systems quickly.

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AGILE Development

What are the steps?

Agile development might best be termed “software engineering lite.”

The basic framework activities— communication, planning, modeling,

construction, and deployment.

But they morph into a minimal task set that pushes the project team
toward construction and delivery (some would argue that this is done
at the expense of problem analysis and solution design).

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