Software Process Model in software engineering

Chapter :Software Process Model

Chapter : Topic Covered
 About software process model
 Build and Fix Model
 Why Models are needed?
 Process as a "black box“ & Problem
 Process as a “white box“ & Advantage
 Prescriptive Model
 Waterfall Model or Linear Sequential
 Incremental Process Models
 Incremental Model
 RAD Model
 Evolutionary Process Models
 Prototyping
 Spiral Model
 Concurrent Development Model
 Fourth Generation Techniques (4GT)
 Component based development (CBD)

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.

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

Why Models are needed?
 Symptoms of inadequacy: the software crisis
 scheduled time and cost exceeded
 user expectations not met
 poor quality

Process as a "black box"
Product
Process
Informal
Requirements
Quality?
Uncertain /
Incomplete requirement
In the beginning

Problems
 The assumption is that requirements can
be fully understood prior to development
 Interaction with the customer occurs
only at the beginning (requirements)
and end (after delivery)
 Unfortunately the assumption almost
never holds

Process as a "white box"
Product
Process
Informal
Requirements
feedback

Advantages
 Reduce risks by improving visibility
 Allow project changes as the project
progresses
 based on feedback from the customer

Prescriptive Model
 Prescriptive process models advocate an orderly approach to software
engineering
 Organize framework activities in a certain order
 Process framework activity with set of software engineering actions.
 Each action in terms of a task set that identifies the work to be
accomplished to meet the goals.
 The resultant process model should be adapted to accommodate the
nature of the specific project, people doing the work, and the work
environment.
 Software engineer choose process framework that includes activities
like;
 Communication
 Planning
 Modeling
 Construction
 Deployment

Prescriptive Model
 Calling this model as “Prescribe”
because it recommend a set of
process elements, activities, action
task, work product & quality.
 Each elements are inter related to
one another (called workflow).

Waterfall Model or Classic Life
Cycle

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.

15
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.

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

 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

 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

Rapid Application Development
(RAD) Model
Makes heavy use of reusable software components with an
extremely short development cycle

RAD model
 Communication – to understand business problem.
 Planning – multiple s/w teams works in parallel on diff.
system.
 Modeling –
 Business modeling – Information flow among
business is working.
Ex. What kind of information drives?
Who is going to generate information?
From where information comes and goes?
 Data modeling – Information refine into set of data
objects that are needed to support business.
 Process modeling – Data object transforms to
information flow necessary to implement business.

 Construction – it highlighting the use of pre-existing
software component.
 Deployment – Deliver to customer basis for
subsequent iteration.
 RAD model emphasize a short development cycle.
 “High speed” edition of linear sequential model.
 If requirement are well understood and project scope is
constrained then it enable development team to create “
fully functional system” within a very short time period.

RAD Model
 If application is modularized (“Scalable Scope”), each
major function to be completed in less than three
months.
 Each major function can be addressed by a separate
team and then integrated to form a whole.
Drawback:
 For large but scalable projects
 RAD requires sufficient human resources
 Projects fail if developers and customers are not
committed in a much shortened time-frame
 Problematic if system can not be modularized
 Not appropriate when technical risks are high ( heavy
use of new technology)

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)

Evolutionary Process Models :
Prototyping

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.

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.

Evolutionary Model: Spiral
Model

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.

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.

 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.

 It represented schematically as series of major technical
activities, tasks, and their associated states.
 It is often more appropriate for system engineering projects
where different engineering teams are involved.
 The activity-modeling may be in any one of the states for a
given time.
 All activities exist concurrently but reside in different states.
E.g.
 The analysis activity (existed in the none state while initial
customer communication was completed) now makes a
transition into the under development state.
 Analysis activity moves from the under development state
into the awaiting changes state only if customer indicates
changes in requirements.
 Series of event will trigger transition from state to state.
E.g. During initial stage there was inconsistency in design which
was uncovered. This will triggers the analysis action from the
Done state into Awaiting Changes state.
Concurrent Development Model

Concurrent Development (Cont.)
 Visibility of current state of project
 It define network of activities
 Each activities, actions and tasks on
the network exists simultaneously
with other activities ,actions and
tasks.
 Events generated at one point in the
process network trigger transitions
among the states.

Fourth Generation Techniques(4GT)

4GT
 Like all other models, 4GT begins with a requirements
gathering phase.
 Ideally, the customer would describe the requirements, which
are directly translated into an operational prototype.
 Practically, however, the client may be unsure of the
requirements, may be ambiguous in his specs or may be
unable to specify information in a manner that a 4GT tool can
use.
 For small applications, it may be possible to move directly from
the requirements gathering phase to the implementation phase
using a nonprocedural fourth generation language.
 However for larger projects a design strategy is necessary.
Otherwise, the same difficulties are likely to arise as with
conventional approaches.

4GT
 To transform a 4GT implementation into a product, the
developer must conduct thorough testing, develop meaningful
documentation.
 In addition, the 4GT developed software must be built in a
manner that enables maintenance to be performed quickly.
Merits:
 Dramatic reduction in software development time. (For small
and intermediate application)
 Improved productivity for software developers.
Demerits:
 Not much easier to use as compared to programming
languages
 The maintainability of large software systems built using 4GT is
open to question.

4GT
 4GT Software tool is used to generate the source code
for a software system from a high level specification
representation
 Commonly used 4GT in development models are
mentioned below:
 Report Generation
 Data base query language
 Data Manipulation
 Screen definition and interaction
 Code Generation
 Web engineering Tools
 high-level graphics

Component Based Development
 component-based development (CBD) model
incorporates many of the characteristics of the
spiral model.
 It is evolutionary by nature and iterative
approach to create software.
 CBD model creates applications from
prepackaged software components (called
classes).

CBD model (cont.)
 Modeling and construction activities begin with identification of
candidate components.
 Classes created in past software engineering projects are
stored in a class library or repository.
 Once candidate classes are identified, the class library is
searched to determine if these classes already exist.
 If class is already available in library extract and reuse it.
 If class is not available in library, it is engineered or developed
using object-oriented methods.
 Any new classes built to meet the unique needs of the
application.
 Now process flow return to the spiral activity.

CBD model (cont.)
 CBD model leads to software
reusability.
 Based on studies, CBD model leads to
70 % reduction in development cycle
time.
 84% reduction in project cost.
 Productivity is very high.

Software Process Model in software engineering

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