Chapter 2
Modeling the
Process and Life
Cycle
Shari L. Pfleeger
Joanne M. Atlee
4th Edition
2.1 The Meaning of Process
• A process: a series of steps involving
activities, constraints, and resources that
produce an intended output of some kind
• A process involves a set of tools and
techniques
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.2
2.1 The Meaning of Process
Process Characteristics
• Prescribes all major process activities
• Uses resources, subject to set of constraints (such as
schedule)
• Produces intermediate and final products
• May be composed of subprocesses with hierarchy or
links
• Each process activity has entry and exit criteria
• Activities are organized in sequence, so timing is clear
• Includes goals of each activity
• Constraints may apply to an activity, resource or
product
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.3
2.1 The Meaning of Process
The Importance of Processes
• Impose consistency and structure on a set of
activities
• Guide us to understand, control, examine, and
improve the activities
• Enable us to capture our experiences and pass
them along
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.4
2.2 Software Process Models
Reasons for Modeling a Process
• To form a common understanding
• To find inconsistencies, redundancies,
omissions
• To find and evaluate appropriate activities
for reaching process goals
• To tailor a general process for a particular
situation in which it will be used
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.5
2.2 Software Process Models
Software Life Cycle
• When a process involves building a software,
the process may be referred to as software
life cycle
–
–
–
–
–
–
Requirements analysis and definition
System (architecture) design
Program (detailed/procedural) design
Writing programs (coding/implementation)
Testing: unit, integration, system
System delivery (deployment)
– Maintenance
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.6
2.2 Software Process Models
Software Development Process Models
•
•
•
•
Waterfall model
V model
Prototyping model
Phased development: increments and
iteration
• Spiral model
• Agile methods
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.7
2.2 Software Process Models
Waterfall Model
• One of the first process development models
proposed
• Works for well understood problems with
minimal or no changes in the requirements
• Simple and easy to explain to customers
• It presents
– a very high-level view of the development process
– sequence of process activities
• Each major phase is marked by milestones
and deliverables (artifacts)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.8
2.2 Software Process Models
Waterfall Model (continued)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.9
2.2 Software Process Models
Drawbacks of The Waterfall Model
• Views software development as manufacturing
process
• No guidance how to handle changes to
products and activities during development
• There is no iteration
• The clients may not know the requirements
• Changing requirements in later stages cause
increased overall project cost
• Long wait before a final product
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.10
2.2 Software Process Models
V Model
•
•
•
•
A variation of the waterfall model
Uses unit testing to verify module design
Uses integration testing to verify system design
Uses acceptance testing to validate the
requirements
• If problems are found during verification and
validation, the left side of the V can be reexecuted before testing on the right side is reenacted
• Adoption by medical device industry
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.11
2.2 Software Process Models
V Model (continued)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.12
2.2 Software Process Models
Drawbacks of The V Model
• Has similar drawbacks as the waterfall model
• Too simple - may not reflect the software
process accurately
• Use of inefficient and ineffective testing
techniques
• Rigid link between left-side and right-side
(acceptance testing corresponds to the user
requirements)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.13
2.2 Software Process Models
Prototyping Model
• Reduces risk and uncertainty in the
development as well as time and cost
• Online systems and HCI
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.14
2.2 Software Process Models
Drawbacks of The Prototype Model
• Not sufficient analysis (functionality, scalability,
maintainability)
• User misunderstanding (prototype vs. final
product)
• Developer misunderstanding the user reqs.
• Too much time spent on prototype
development
– Increased cost
– Increased involvement and attachment to prototype
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.15
2.2 Software Process Models
Phased Development: Increments and Iterations
• Shorter cycle time
• System delivered in pieces
– enables customers to have some functionality
while the rest is being developed
• Allows two systems functioning in parallel
– the production system (release n): currently being
used
– the development system (release n+1): the next
version
• Supported by US DoD, NASA
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.16
2.2 Software Process Models
Phased Development: Increments and Iterations
(continued)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.17
2.2 Software Process Models
Phased Development: Increments and Iterations
(continued)
• Incremental development: starts with small functional
subsystem and adds functionality with each new release
• Iterative development: starts with full system, then
changes functionality of each subsystem with each new
release
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.18
2.2 Software Process Models
Phased Development: Increments and Iterations
(continued)
• Phased development is desirable for several
reasons
– Markets can be created early for functionality that
has never before been offered
– The development team can focus on different areas
of expertise with different releases
– Easier to test and debug
– Regression testing after each iteration
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.19
2.2 Software Process Models
Spiral Model
• Suggested by Boehm (1988)
• Combines development activities with risk
management to minimize and control risks
• The model is presented as a spiral in which
each iteration is represented by a circuit
around four major activities
–
–
–
–
Plan
Determine goals, alternatives and constraints
Evaluate alternatives and risks
Develop and test
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.20
2.2 Software Process Models
Spiral Model (continued)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.21
2.2 Software Process Models
Agile Methods
• Emphasis on flexibility in producing software
quickly and capably
• Agile manifesto
– Value individuals and interactions over process and
tools
– Prefer to invest time in producing working software
rather than in producing comprehensive
documentation
– Focus on customer collaboration rather than
contract negotiation
– Concentrate on responding to change rather than on
creating a plan and then following it
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.22
2.2 Software Process Models
Agile Methods: Examples of Agile Process
• Extreme programming (XP)
• Scrum: 30-day iterations; multiple selforganizing teams; daily “scrum” coordination
• Adaptive software development (ASD)
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.23
2.2 Software Process Models
Agile Methods: Extreme Programming
• Emphasis on four charateristics of agility
– Communication: continual interchange between
customers and developers
– Simplicity: select the simplest design or
implementation
– Courage: commitment to delivering functionality
early and often
– Feedback: loops built into the various activitites
during the development process
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.24
2.2 Software Process Models
Agile Methods: Twelve Facets of XP
• Planning game
(weekly meeting or per iteration)
• Small release
(weeks rather than months)
•
•
•
•
Common vision
Simple design
Writing tests first
Refactoring
• Pair programming
• Collective ownership
• Continuous integration
(small increments)
• Sustainable pace
hours/week)
(40
• On-site customer
• Coding standard
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.25
2.2 Software Process Models
Extreme Programming
• Frequent releases in short development
cycles to achieve higher quality and
productivity
• Programming pairs, extensive code review,
and unit testing
• Frequent communication with the customer
and programmers
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.26
2.2 Software Process Models
Sidebar 2.2 When Extreme is Too Extreme?
• XP's practices are interdependent
– A vulnerability if one of them is modified
• Requirements expressed as a set of test cases
must be passed by the software
– System passes the tests but is not what the customer is
paying for
• Refactoring issue
– Difficult to rework a system w/o degrading architecture
• User stories: scalability, vague, incomplete, nonfunctional requirements
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.27
2.2 Software Process Models
Agile Methods: Scrum
•
•
•
•
30-day iterations
multiple self-organizing teams
daily “scrum” coordination
three roles: product owner, development
team, and scrum master
• sprint (iteration): basic unit in scrum
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.28
2.3 Tools and Techniques for Process
Modeling
• Notation depends on what we want to
capture in the model
• The two major notation categories
– Static model: depicts the process
– Dynamic model: enacts the process
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.29
2.3 Tools and Techniques for Process Modeling
Static Modeling: Lai Notation
• Element of a process are viewed in terms of
seven types
–
–
–
–
–
–
–
Activity
Sequence
Process model
Resource
Control
Policy
Organization
• Several templates, such as an Artifact
Definition Template
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.30
2.3 Tools and Techniques for Process Modeling
Static Modeling: Lai Notation
Name
Synopsis
Complexity type
Data type
Artifact-state list
parked
initiated
moving
Car
This is the artifact that represents a class of cars.
Composite
(car_c, user-defined)
((state_of(car.engine) = off)
(state_of(car.gear) = park)
(state_of(car.speed) =
stand))
((state_of(car.engine) = on)
(state_of(car.key_hole) =
has-key)
(state_of(car-driver(car.))
= in-car)
(state_of(car.gear) = drive)
(state_of(car.speed) =
stand))
((state_of(car.engine) = on)
(state_of(car.keyhole) =
has-key)
(state_of(car-driver(car.))
= driving)
((state_of(car.gear) =
drive) or (state_of(car.gear)
= reverse))
((state_of(car.speed) =
stand) or
(state_of(car.speed) = slow)
or (state_of(car.speed) =
medium) or
(state_of(car.speed) =
high))
Car is not moving, and
engine is not running.
doors
engine
keyhole
The four doors of a car.
The engine of a car.
The ignition keyhole of a
car.
The gear of a car.
The speed of a car.
Car is not moving, but the
engine is running
Car is moving forward or
backward.
Sub-artifact list
gear
speed
Relations list
car-key
car-driver
This is the relation between a car and a key.
This is the relation between a car and a driver.
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.31
2.3 Tools and Techniques for Process Modeling
Static Modeling: Lai Notation (continued)
• The process of starting a car
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.32
2.3 Tools and Techniques for Process Modeling
Static Modeling: Lai Notation (continued)
• Transition diagram illustrates the transition
for a car
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.33
2.3 Tools and Techniques for Process Modeling
Dynamic Modeling
• Enables enaction of process to see what
happens to resources and artifacts as
activities occur
• Simulate alternatives and make changes to
improve the process
• Example: systems dynamics model
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.34
2.3 Tools and Techniques for Process Modeling
Dynamic Modeling: System Dynamics (continued)
• Pictorial presentation of factors affecting productivity
• Arrows indicate how changes in one factor change
another
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.35
2.5. Information System Example
Piccadilly Television Advertising System
• Needs a system that is easily maintained and
changed
• Requirements may change
– Waterfall model is not applicable
• User interface prototyping is an advantage
• There is uncertainty in regulation and
business constraints
– Need to manage risks
• Spiral model is the most appropriate
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.36
2.5. Information System Example
Piccadilly System (continued)
• Risk can be viewed in terms of two facets
– Probability: the likelyhood a particular problem
may occur
– Severity: the impact it will have on the system
• To manage risk, it needs to include
characterization of risks in the process
model
– Risk is an artifact that needs to be described
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.37
2.5. Information System Example
Lai Artifact Table for Piccadilly System
Name
Synopsis
Complexity type
Data type
Artifact-state list
low
Risk (problemX)
This is the artifact that represents the risk that problem X
will occur and have a negative affect on some aspect of the
development process.
Composite
(risk_s, user_defined)
((state_of(probability.x) = low)
(state_of(severity.x) = small))
high-medium
((state_of(probability.x) = low)
(state_of(severity.x) = large))
low-medium
((state_of(probability.x) = high)
(state_of(severity.x) = small))
high
((state_of(probability.x) = high)
(state_of(severity.x) = large))
Probability of problem is
low, severity problem
impact is small.
Probability of problem is
low, severity problem
impact is large.
Probability of problem is
high, severity problem
impact is small.
Probability of problem is
high, severity problem
impact is large.
Sub-artifact list
probability.x
severity.x
Pfleeger and Atlee, Software Engineering: Theory and Practice
The probability that
problem X will occur.
The severity of the
impact should problem
X occur on the project.
Chapter 2.38
2.6 Real Time Example
Ariane-5 Software
• Involved reuse of software from Ariane-4
• The reuse process model
– Identify resuable subprocesses, describe them
and place them in a library
– Examine the requirements for the new software
and the reusable components from library and
produce revised set of requirements
– Use the revised requirements to design the
software
– Evaluate all reused design components to certify
the correctness and consistency
– Build or change the software
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.39
2.6 Real Time Example
Ariane-5 Software (continued)
• Reuse process model presentation
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.40
2.7 What this Chapter Means for You
• Process development involves activities,
resources, and product
• Process model includes organizational,
functional, behavioral and other prespectives
• A process model is useful for guiding team
behavior, coordination and collaboration
Pfleeger and Atlee, Software Engineering: Theory and Practice
Chapter 2.41