Software_Process_Model for class.ppt

Chapter :Software Process Model
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Chapter : Topic Covered
 About software process model
 Build and Fix Model
 Why Models are needed?
 Prescriptive Model
 Waterfall Model or Linear Sequential
 Incremental Process Models
 Incremental Model
 RAD Model
 Evolutionary Process Models
 Prototyping
 Spiral Model
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Software process model
 Process models prescribe a distinct set of activities,
actions, tasks, milestones, and work products required to
engineer high quality software.
 Process models are not perfect, but provide roadmap for
software engineering work.
 Software models provide stability, control, and
organization to a process that if not managed can easily
get out of control
 Software process models are adapted to meet the needs
of software engineers and managers for a specific
project.
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Build and Fix Model
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Build and Fix Model
The earlier approach
 Product is constructed without specification or any
attempt at design.
 developers simply build a product that is reworked as
many times as necessary to satisfy the client.
 model may work for small projects but is totally
unsatisfactory for products of any reasonable size.
 Maintenance is high.
 Source of difficulties and deficiencies
 impossible to predict
 impossible to manage
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Why Models are needed?
 Symptoms of inadequacy: the software crisis
 scheduled time and cost exceeded
 user expectations not met
 poor quality
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Waterfall Model or Classic Life
Cycle
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Waterfall Model or Classic Life
Cycle
 Requirement Analysis and Definition: What - The systems services, constraints
and goals are defined by customers with system users.
 Scheduling tracking -
 Assessing progress against the project plan.
 Require action to maintain schedule.
 System and Software Design: How –It establishes and overall system
architecture. Software design involves fundamental system abstractions and their
relationships.
 Integration and system testing: The individual program unit or programs are
integrated and tested as a complete system to ensure that the software
requirements have been met. After testing, the software system is delivered to
the customer.
 Operation and Maintenance: Normally this is the longest phase of the software
life cycle. The system is installed and put into practical use. Maintenance involves
correcting errors which were not discovered in earlier stages of the life-cycle.
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11
Limitations of the waterfall
model
 The nature of the requirements will not change very much During
development; during evolution
 The model implies that you should attempt to complete a given stage
before moving on to the next stage
 Does not account for the fact that requirements constantly change.
 It also means that customers can not use anything until the entire
system is complete.
 The model implies that once the product is finished, everything else is
maintenance.
 Surprises at the end are very expensive
 Some teams sit ideal for other teams to finish
 Therefore, this model is only appropriate when the requirements are
well-understood and changes will be fairly limited during the design
process.
Problems:
1. Real projects are rarely follow the sequential model.
2. Difficult for the customer to state all the requirement explicitly.
3. Assumes patience from customer - working version of program will not
available until programs not getting change fully.
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Incremental Process Model
C- Communication
P - Planning
M – Modeling
C - Construction
D - Deployment
Delivers software in small but usable pieces, each piece builds on
pieces already delivered Vishnu Priya P M 12

 Rather than deliver the system as a single delivery, the development
and delivery is broken down into increments with each increment
delivering part of the required functionality.
 First Increment is often core product
 Includes basic requirement
 Many supplementary features (known & unknown) remain
undelivered
 A plan of next increment is prepared
 Modifications of the first increment
 Additional features of the first increment
 It is particularly useful when enough staffing is not available for the
whole project
 Increment can be planned to manage technical risks.
 Incremental model focus more on delivery of operation product with
each increment.
The Incremental Model
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 User requirements are prioritised and the highest priority requirements
are included in early increments.
 Once the development of an increment is started, the requirements are
frozen though requirements for later increments can continue to
evolve.
 Customer value can be delivered with each increment so system
functionality is available earlier.
 Early increments act as a prototype to help elicit requirements for later
increments.
 Lower risk of overall project failure.
 The highest priority system services tend to receive the most testing.
The Incremental Model
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Evolutionary Process Model
 Produce an increasingly more
complete version of the software with
each iteration.
 Evolutionary Models are iterative.
 Evolutionary models are:
 Prototyping
 Spiral Model
 Concurrent Development Model
 Fourth Generation Techniques (4GT)
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Evolutionary Process Models :
Prototyping
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Prototyping cohesive
 Best approach when:
 Objectives defines by customer are general but does not have
details like input, processing, or output requirement.
 Developer may be unsure of the efficiency of an algorithm, O.S.,
or the form that human machine interaction should take.
 It can be used as standalone process model.
 Model assist software engineer and customer to better understand
what is to be built when requirement are fuzzy.
 Prototyping start with communication, between a customer and
software engineer to define overall objective, identify requirements and
make a boundary.
 Going ahead, planned quickly and modeling (software layout visible to
the customers/end-user) occurs.
 Quick design leads to prototype construction.
 Prototype is deployed and evaluated by the customer/user.
 Feedback from customer/end user will refine requirement and that is
how iteration occurs during prototype to satisfy the needs of the
customer.
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Prototyping (cont..)
 Prototype can be serve as “the first system”.
 Both customers and developers like the prototyping paradigm.
 Customer/End user gets a feel for the actual system
 Developer get to build something immediately.
Problem Areas:
 Customer cries foul and demand that “a few fixes” be applied to make
the prototype a working product, due to that software quality suffers
as a result.
 Developer often makes implementation in order to get a prototype
working quickly without considering other factors in mind like OS,
Programming language, etc.
Customer and developer both must be agree that the prototype is built to
serve as a mechanism for defining requirement.
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Evolutionary Model: Spiral
Model
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Spiral Model
 Couples iterative nature of prototyping with the controlled and
systematic aspects of the linear sequential model
 It provide potential for rapid development of increasingly more
complete version of the software.
 Using spiral, software developed in as series of evolutionary
release.
 Early iteration, release might be on paper or prototype.
 Later iteration, more complete version of software.
 Divided into framework activities (C,P,M,C,D). Each activity
represent one segment.
 Evolutionary process begins in a clockwise direction, beginning
at the center risk.
 First circuit around the spiral might result in development of a
product specification. Subsequently, develop a prototype and
then progressively more sophisticated version of software.
 Unlike other process models that end when software is
delivered.
 It can be adapted to apply throughout the life of software.
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Spiral Model
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Spiral Model (cont.)
Concept Development Project:
 Start at the core and continues for multiple iterations until it is
complete.
 If concept is developed into an actual product, the process
proceeds outward on the spiral.
New Product Development Project:
 New product will evolve through a number of iterations around
the spiral.
 Later, a circuit around spiral might be used to represent a
“Product Enhancement Project”
Product Enhancement Project:
 There are times when process is dormant or software team not
developing new things but change is initiated, process start at
appropriate entry point.
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 Spiral models uses prototyping as a risk reduction
mechanism but, more important, enables the developer
to apply the prototyping approach at each stage in the
evolution of the product.
 It maintains the systematic stepwise approach suggested
by the classic life cycle but also incorporates it into an
iterative framework activity.
 If risks cannot be resolved, project is immediately
terminated
Problem Area:
 It may be difficult to convince customers (particularly in
contract situations) that the evolutionary approach is
controllable.
 If a major risk is not uncovered and managed, problems
will undoubtedly occur.
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