3. ch 2-process model

Chapter-2: Process Models
Abdus Sattar
Senior Lecturer
Department of Computer Science and Engineering
Daffodil International University
Email: abdus.cse@diu.edu.bd

Definition of Software Process
 Software Process:
o A framework for the activities, actions, and tasks that
are required to build high-quality software.
o SP defines the approach that is taken as software is
engineered.
o Is not equal to software engineering, which also
encompasses technologies that populate the process–
technical methods and automated tools.
 Process Model :
o A Process Model describes the sequence of phases for
the entire lifetime of a product. Therefore it is sometimes
also called Product Life Cycle.
o This covers everything from the initial commercial idea
until the final de-installation or disassembling of the
product after its use. 2

What / who / why is Process
Models?
What: Go through a series of predictable steps--- a road map that
helps you create a timely, high-quality results.
Who: Software engineers and their managers, clients also. People
adapt the process to their needs and follow it.
Why: Provides stability, control, and organization to an activity that
can if left uncontrolled, become quite chaotic. However, modern
software engineering approaches must be agile and demand ONLY
those activities, controls and work products that are appropriate.
What Work products: Programs, documents, and data
What are the steps: The process you adopt depends on the software
that you are building. One process might be good for aircraft avionic
system, while an entirely different process would be used for
website creation.
How to ensure right: A number of software process assessment
mechanisms that enable us to determine the maturity of the software
process. However, the quality, timeliness and long-term viability of
the software are the best indicators of the efficacy of the process you
use.
3

A Generic Process Model
4
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.
Next question is: how the framework activities and the actions
and tasks that occur within each activity are organized with
respect to sequence and time? See the process flow for
answer.

A Generic Process Model
5
• Communication : This activity involves heavy communication with
customers and other stakeholders in order to gather requirements
and other related activities.
• Planning : Here a plan to be followed will be created which will
describe the technical tasks to be conducted, risks, required
resources, work schedule etc.
• Modeling : A model will be created to better understand the
requirements and design to achieve these requirements.
• Construction : Here the code will be generated and tested.
• Deployment : Here, a complete or partially complete version of the
software is represented to the customers to evaluate and they give
feedbacks based on the evaluation.

Process
Flow
7
Framework Activities

Process Flow
9
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.

Identifying a Task Set
10
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 of a Task Set for
Elicitation
11
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.

Example of a Task Set for
a big project
12
 The task sets for Requirements gathering action for a big project may
include:
1. Make a list of stakeholders for the project.
2. Interview each stakeholders separately to determine overall wants and
needs.
3. Build a preliminary list of functions and features based on stakeholder
input.
4. Schedule a series of facilitated application specification meetings.
5. Conduct meetings.
6. Produce informal user scenarios as part of each meeting.
7. Refine user scenarios based on stakeholder feedback.
8. Build a revised list of stakeholder requirements.
9. Use quality function deployment techniques to prioritize requirements.
10. Package requirements so that they can be delivered incrementally.
11. Note constraints and restrictions that will be placed on the system.
12. Discuss methods for validating the system.

Process Patterns
13
A process pattern
 describes a process-related problem that is
encountered during software engineering work,
 identifies the environment in which the problem
has been encountered, and
 suggests one or more proven solutions to the
problem.

Process Patterns
14
 Template for describing a process pattern:
 Pattern Name:
 The pattern name is given a meaningful name that describe its
function within software process.
 Example: Customer-Communication
 Intent:
 The objective of this pattern is describe briefly.
 Example: Intent of the communication customer to connection
establish with customer.
 Type:
 The pattern type is specified.
 Three types:
 Task Pattern - action or work task
 Stage Pattern – frame activity.
 Phase Pattern – sequence of frame.

Process Patterns (Cont…)
15
 Initial Context:
 Describe which pattern are applies
 Prior to the initialization of the pattern.
 Resulting Context:
 The condition that will result once the pattern has been successfully
implementers are describe.
 Related Pattern:
 A list of process pattern that are directly related to this one are
provided as a hierarchy on in some other diagrammatic form.

Software Process Model
16
A Process Model describes the sequence of
phases for the entire lifetime of a product.
It is sometimes also called Product Life
Cycle.
This covers everything from the initial
commercial idea until the final de-
installation or disassembling of the product
after its use
All software process models can
accommodate the generic framework
activities.

Waterfall Model (Cont..)
18
• The first published model of the software development process
was derived from more general system engineering processes
(Royce, 1970).
• This model is known as the ‘waterfall model’ or software life
cycle
• The waterfall model This takes the fundamental process
activities of specification, development, validation, and
evolution and represents them as separate process phases such
as requirements specification, software design,
implementation, testing, and so on.

19
The sequential phases in Waterfall model are:
 Requirement Gathering and analysis: All possible requirements of the system to be
developed are captured in this phase and documented in a requirement specification
doc.
 System Design: The requirement specifications from first phase are studied in this
phase and system design is prepared. System Design helps in specifying hardware
and system requirements and also helps in defining overall system architecture.
 Implementation: With inputs from system design, the system is first developed in
small programs called units, which are integrated in the next phase. Each unit is
developed and tested for its functionality which is referred to as Unit Testing.
 Integration and Testing: All the units developed in the implementation phase are
integrated into a system after testing of each unit. Post integration the entire system is
tested for any faults and failures.
 Deployment of system: Once the functional and non functional testing is done, the
product is deployed in the customer environment or released into the market.
 Maintenance: There are some issues which come up in the client environment. To
fix those issues patches are released. Also to enhance the product some better
versions are released. Maintenance is done to deliver these changes in the customer
environment.

20
Problems:
 Real projects rarely follow the sequential flow that the
model proposes. Although the linear model can
accommodate iteration, it does so indirectly. As a result,
changes can cause confusion as the project team proceeds.
 It is often difficult for the customer to state all requirements
explicitly. The waterfall model requires this and has
difficulty accommodating the natural uncertainty that exists
at the beginning of many projects.
 The customer must have patience. A working version of the
program(s) will not be available until late in the project time
span. A major blunder, if undetected until the working
program is reviewed, can be disastrous.

21
Problems:
 Rarely linear, iteration needed.
 Hard to state all requirements explicitly. Blocking state.
 Code will not be released until very late.
Waterfall Model Application
 Every software developed is different and requires a suitable SDLC approach to
be followed based on the internal and external factors. Some situations where
the use of Waterfall model is most appropriate are:
 Requirements are very well documented, clear and fixed.
 Product definition is stable.
 Technology is understood and is not dynamic.
 There are no ambiguous requirements.
 Ample resources with required expertise are available to support the product.
 The project is short.

The V-Model(Cont..)
23
 The V - model is SDLC model where execution of processes
happens in a sequential manner in V-shape.
 It is also known as Verification and Validation model.
 V - Model is an extension of the waterfall model and is based
on association of a testing phase for each corresponding
development stage. This means that for every single phase in
the development cycle there is a directly associated testing
phase.
This is a highly disciplined model and next phase starts only
after completion of the previous phase.

The V-Model(Cont..)
24
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.

The Incremental Model(Cont..)
26
 The incremental model combines element of waterfall model
applied in an iterative fashion.
 The incremental model applies linear sequence like as calendar
time progresses. Each linear sequence.
 For Example:-
 Word processing software development using the incremental
paradigm.
 Basic file management, editing, document production function in
the first increment.
 More sophisticated editing, and document production capabilities in
the second increment.
 Spelling and grammar checking in the third increment.
 Advance page layout capability in the fourth.

The Spiral Model(Cont..)
28
 The spiral model is a evolutionary software process model
that couples the iterative nature of prototyping with the
controlled and systematic aspect of the waterfall model.
 It provides the potential for rapid development of increasingly
more complete version of the software.
 A spiral model is divided into a set of framework activities
defined by software engineering team. Each framework
activities represent one segment of the spiral path.
 Activities are implied by a circuit around the spiral clockwise
direction, beginning at the center.

The Spiral Model(Cont..)
29
 Concept development project
 Which starts at the core of the spiral and continues for multiple
iteration.
 New product development
 The new product will develop through a number of iteration around the spiral.
 The spiral model is a realistic approach to development of
large scale system and software. Because software
development the process progresses.

Concurrent Model(Cont..)
31
The concurrent development model - called concurrent
engineering
It provides an accurate state of the current state of a project.
Focus on concurrent engineering activities in a software
engineering process such as prototyping, analysis modeling,
requirements specification and design.
Represented schematically as a series of major technical
activities, tasks and their associated states.
Defined as a series of events that trigger transitions from
state to state for each of the software engineering activities.

Concurrent Model(Cont..)
32
Often used as the paradigm for the development of
client/server applications. A client/server system is
composed of a set of functional components.
When applied to client/server, the concurrent process
model defines activities in two dimensions :
(i) System dimension -System level issues are addressed
using three activities: design, assembly, and use.
(ii) The component dimension is addressed with two
activities: design and realization.

Unified Process Model
33
 Unified process (UP) is an architecture-centric, use-case
driven, iterative and incremental development process that
leverages unified modeling language and is compliant with
the system process engineering meta-model.
 Unified process can be applied to different software systems
with different levels of technical and managerial complexity
across various domains and organizational cultures.
 UP is also referred to as the unified software development
process.

36
References:
1. Software Engineering A practitioner’s
Approach
by Roger S. Pressman, 7th edition, McGraw Hill, 2010.
2. Software Engineering by Ian Sommerville,
9th edition, Addison-Wesley, 2011

3. ch 2-process model

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