CSE 436—Personal
Software Processes, Software
Development Models
Ron K. Cytron
http://www.cs.wustl.edu/~cytron/cse436/
9 October 2006
Today
• Personal Software Processes
• Groups present requirements (postponed to next week)
– How did you elicit the requirements?
– How are the requirements structured?
– What interactions do you require with the customer to firm up
the requirements
• Software development processes
• Break
• Groups discuss architecture
–
–
–
–
Break down project into pieces
Articulate integration and demonstration points
Plan schedule
Present architecture ideas to class
CSE 436 Software Engineering Workshop
PSP–Personal Software Process
• What is this?
– Self-improvement process
• Managing time and other spare resources
• Becoming more effective, productive, valuable
– Increased awareness
• Productivity enhancement
• Feasibility
• Quality issues
• Why?
– How do you know where you are?
– How do you know where to go?
– How do you know how to get there?
CSE 436 Software Engineering Workshop
Baseline Personal Process (PSP0)
• Planning
–
–
–
–
Summary and overview
Get or develop requirements
Fill out plan summary
Entry in time recording log
• Development
–
–
–
–
–
Design the program
Implement the design
Compile, fix and log all defects
Test, fix and log more defects
Entry in time recording log
• Post Mortem
– Complete project plan summary
• Estimated and actual data
– Complete time and defect logs
• Today: Planning
CSE 436 Software Engineering Workshop
PSP0 Plan Summary
Time in Phase (min)
Planning
Design
Code
Compile
Test
Postmortem
Total
Plan
This Project
5
30
32
15
5
30
180
117
All Projects
48
46
77
44
36
57
308
All Programs %
15.6%
14.9%
25.0%
14.3%
11.7%
18.5%
100.0%
Defects Injected
Planning
Design
Code
Compile
Test
Total Development
0
2
5
0
0
7
0
2
5
0
4
11
0.0%
18.2%
45.5%
0.0%
36.4%
100.0%
Defects Removed
Planning
Design
Code
Compile
Test
Total Development
After Development
0
0
0
6
1
7
0
0
0
0
10
1
11
0
0.0%
0.0%
0.0%
90.6%
9.4%
100.0%
CSE 436 Software Engineering Workshop
PSP0 Planning-Phase Script
1. Requirements
•
•
•
Elicit
Elaborate
Validate
2. Resource estimation
•
•
Best estimate
Will serve as area of “personal improvement”
3. Exit criteria
•
•
Documentation
• Summary and Overview
• Requirements tabulated
• Estimated time for the project
Entry in time log for this phase
CSE 436 Software Engineering Workshop
Software Process Models
• Distinct set of activities, actions, tasks,
milestones, work products
• Agreed upon by management and engineers
• Adds stability, control to an organization
• Steps vary by method
• Work products are code, documentation, data
• This is an area where WU students are deemed
deficient by interviewers.
• Take note:
– Waterfall
– Spiral
– XP (Extreme Programming)
CSE 436 Software Engineering Workshop
Waterfall Model
• Also called classic life cycle, proposed by
Winston Royce in 1970
• Original proposal allowed for feedback and
loops
• In practice, strictly linear
• Called a “prescriptive” process model
CSE 436 Software Engineering Workshop
Waterfall Model
• Communication
– Initiation, requirements gathering
• Planning
– Estimating, scheduling, tracking mechanisms
• Modeling
– Analysis and design
• Construction
– Code and test
• Deployment
– Delivery, support, feedback
CSE 436 Software Engineering Workshop
Waterfall Model
• Real projects find it difficult to be so “linear”
• Customers have trouble stating requirements
consistently, accurately, minimally.
– Model does not account for uncertainty
• Working version of program not realized until
end of model
– Tracking functional and nonfunctional properties is
hard
– Customer confidence can become weak
• Model may work “in the small” but fails “in the
large”
CSE 436 Software Engineering Workshop
Incremental Models
• All perform some kind of iteration over waterfall
model
• Waterfall becomes a pipeline, with next iteration
starting when requirements change or become
more clear
1
functionality
1.
Communication
2.
Planning
3.
Design/Modeling
4.
Construction
5.
Deployment
1
1
2
2
2
3
3
3
4
4
4
5
time
CSE 436 Software Engineering Workshop
5
5
RAD–Rapid Application Deployment
•
•
•
•
Breaks problem into pieces
Utilizes concurrent design and construction
Huge integration exercise at the end
Alleged 60-90 day time span
Communication
Planning
Design
Construction
Design
Design
Construction
Construction
Deployment
CSE 436 Software Engineering Workshop
RAD drawbacks
• Requires sufficient human resources
• Must commit to rapid development process
– Vision of design must remain consistent among
teams
– Tends to fade or become chaotic over time
• Requires a project that can be componentized
• Levels of abstraction and insulation between
teams can cause performance issues
• Use of cutting-edge technology in one team can
sink the whole project if it fails
CSE 436 Software Engineering Workshop
Evolutionary Models
• Examples
– Prototyping
– Spiral
– Concurrent Development
• Iterative approaches
• Increasingly more complete versions of the
product are generated
• Articulated deliveries can help planning
– Revising design delivers a more on-target product
– Revisiting implementation can remedy a bad initial
approach
– Must avoid urge to begin over completely
CSE 436 Software Engineering Workshop
Prototyping Model
Communication
Quick plan
Quick design
Deployment, delivery, feedback
Construction of prototype
CSE 436 Software Engineering Workshop
Prototyping Model
• Useful when
– Insufficient requirements exist at start
– Behavior of some components unknown
• New or strange OS
• Hardware “in progress”
• HCI (Human-Computer Interface) factors not yet firm
• Algorithmic uncertainties: speed, space
• However
– Testing may be minimal
– Not intended for ultimate delivery of longevity
– Little or no documentation is produced
• Customer and team must agree on this approach upfront
• Expectations should not be overly high on either side
CSE 436 Software Engineering Workshop
Schedule
• No group meetings this (Oct 13) or next Friday
(Oct 20,fall break)
• In class 16 October, prepare to present
requirements and refined architecture
decomposition
CSE 436 Software Engineering Workshop