Software Engineering(unit 1)

SOFTWARE ENGINEERING
UNIT-I
Ms SURBHI SAROHA(Assistant Professor) 1

Software engineering
 Software Engineering is the application
of engineering to the development of software in a
systematic method.
 "The application of a systematic, disciplined,
quantifiable approach to the development,
operation, and maintenance of software"—
IEEE Standard Glossary of Software Engineering
Terminology

Software Life Cycle Models
 The goal of Software Engineering is to provide
models and processes that lead to the production of
well-documented maintainable software in a
manner that is predictable.

Software Life Cycle Models
 “The period of time that starts when a software product is
conceived and ends when the product is no longer
available for use.
 The software life cycle typically includes a requirement
phase, design phase, implementation phase, test phase,
installation and check out phase, operation and
maintenance phase, and sometimes retirement phase”.

Build & Fix Model
 Build
 Code
 Fix
 Product is constructed without
specifications or any attempt at design
Adhoc approach and not well defined
Simple two phase model

Build & Fix Model

Build & Fix Model
Suitable for small programming exercises of
100 or 200 lines
Unsatisfactory for software for any
reasonable size
Code soon becomes unfixable &
unenhanceable
No room for structured design
Maintenance is practically not possible

Waterfall Model
 This model is named “waterfall model” because its
diagrammatic representation resembles a cascade of
waterfalls.

Waterfall Model

Problems of waterfall model
 It is difficult to define all requirements at the
beginning of a project
 This model is not suitable for accommodating any
change
 A working version of the system is not seen until late
in the project’s life
 It does not scale up well to large projects.
 Real projects are rarely sequential.

Incremental Process Model
 They are effective in the situations where
requirements are defined precisely and there is no
confusion about the functionality of the final product.
 After every cycle a useable product is given to the
customer.
Popular particularly when we have to quickly
deliver a limited functionality system.

Iterative Enhancement Model
 This model has the same phases as the waterfall model, but
with fewer restrictions. Generally the phases occur in the
same order as in the waterfall model, but they may be
conducted in several cycles. Useable product is released at
the end of the each cycle, with each release providing
additional functionality.
 Customers and developers specify as many requirements as
possible and prepare a SRS document.
 Developers and customers then prioritize these requirements
 Developers implement the specified requirements in one or
more cycles of design, implementation and test based on the
defined priorities.

Iterative Enhancement Model

Rapid Application Development(RAD) Model
◦ Build a rapid prototype
◦ Give it to user for evaluation & obtain feedback
◦ Prototype is refined
 With active participation of users

Rapid Application Development(RAD) Model

Evolutionary process model
 Evolutionary process model resembles
iterative enhancement model. The same
phases as defined for the waterfall model
occur here in a cyclical fashion.
 This model differs from iterative
enhancement model in the sense that this
does not require a useable product at the
end of each cycle.
 In evolutionary development, requirements
are implemented by category rather than
by priority.

Cont….
 This model is useful for projects using new technology
that is not well understood.
 Functionality must be delivered at one time, but the
requirements are unstable or not well understood at the
beginning.

Evolutionary process model

Prototype Model
 The prototype may be a usable program but is not
suitable as the final software product.
 The code for the prototype is thrown away. However
experience gathered helps in developing the actual
system.
 The development of a prototype might involve extra cost,
but overall cost might turnout to be lower than that of an
equivalent system developed using the waterfall model.

Prototype Model

Spiral Model
 Models do not deal with uncertainly which is
inherent to software projects.
 Important software projects have failed
because project risks were neglected & nobody
was prepared when something unforeseen
happened.
 Barry Boehm recognized this and tired to
incorporate the “project risk” factor into a life
cycle model.
 The result is the spiral model, which was
presented in 1986.

Spiral Model
 The radial dimension of the model represents the cumulative
costs. Each path around the spiral is indicative of increased
costs. The angular dimension represents the progress made in
completing each cycle. Each loop of the spiral from X-axis
clockwise through 360o represents one phase. One phase is
split roughly into four sectors of major activities.
 Planning: Determination of objectives, alternatives &
constraints.
 Risk Analysis: Analyze alternatives and attempts to
identify and resolve the risks involved.
 Development: Product development and testing product.
 Assessment: Customer evaluation

Cont…
 An important feature of the spiral model is that each phase is
completed with a review by the people concerned with the project
(designers and programmers)
 The advantage of this model is the wide range of options to
accommodate the good features of other life cycle models.
 It becomes equivalent to another life cycle model in appropriate
situations.
 The spiral model has some difficulties that need to be resolved
before it can be a universally applied life cycle model. These
difficulties include lack of explicit process guidance in determining
objectives, constraints, alternatives; relying on risk assessment
expertise; and provides more flexibility than required for many
applications.

Spiral Model

 THANK YOU

Software Engineering(unit 1)

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