CS 5150
Software Engineering
Lecture 2
Software Processes
CS 5150
1
Administration
Project teams
• Any announcement to class?
• People who would like to form teams?
CS 5150
2
Administration
Project teams
When you have formed your team and reached
agreement with your client, please send a
message to:
wya@cs.cornell.edu and afix.cs.cornell.edu
with the names of the team, the client's name,
and the topic of the project.
CS 5150
3
A Classic Book
Frederick P. Brooks, Jr. The Mythical Man Month.
Addison-Wesley, 1972.
CS 5150
4
Software Process
Fundamental Assumption:
Good processes lead to good software
Good processes reduce risk
Good processes enhance visibility
CS 5150
5
Variety of Software Processes
Software products are very varied...
Therefore, there is no standard process for all software
engineering projects
BUT successful software development projects all need to
address similar issues.
This creates a number of process steps that must be part of all
software projects
CS 5150
6
Basic Process Steps in all Software Development
• Feasibility and planning
• Requirements
• System and program design
• Implementation and testing
• Acceptance testing and release
• Operation and maintenance
It is essential to distinguish among these process steps and
to be clear which you are are doing at any given moment.
Do not confuse requirements and design
CS 5150
7
Process Step: Feasibility and Planning
A feasibility study precedes the decision to begin a project.
• What is the scope of the proposed project?
• Is the project technically feasible?
• What are the projected benefits?
• What are the costs, timetable?
A feasibility study leads to a decision: go or no-go.
CS 5150
8
Process Step: Requirements
Requirements define the function of the system from the
client's viewpoint.
The requirements establish the system's functionality,
constraints and goals by consultation with the client and
users.
They are specified in a manner that is understandable by
both the client and the development staff.
CS 5150
9
Process Step: System and Program Design
Design describes the system from the software
developers' viewpoint
System design: Match the requirements to hardware or
software systems. Establishes an overall system
architecture
Program design: Represent the software system
functions in a form that can be transformed into one or
more executable programs
CS 5150
10
Process Step: Implementation and Testing
Implementation (coding)
The software design is realized as a set of programs or
program units. (The software components may be
written specifically, acquired from elsewhere, or
modified.)
Testing
Individual components are tested against specifications.
The components are integrated and tested against the
design by the development staff as a complete system.
CS 5150
11
Process Step: Acceptance Testing and Release
Acceptance testing
The system is tested against the requirements by the
client.
Delivery and release
The system is delivered to the client and released into
production.
CS 5150
12
Process Step: Operation and Maintenance
Operation: The system is put into practical use.
Maintenance: Errors and problems are identified and
fixed.
Evolution: The system evolves over time as requirements
change, to add new functions or adapt the technical
environment.
Phase out: The system is withdrawn from service.
This is sometimes called the Software Life Cycle
CS 5150
13
Sequence of Processes
Every software project will include these basic processes, in some
shape or form, but:
•
They may be formal or informal
•
They may be carried out in various sequences
CS 5150
14
Sequence of Processes
Major alternatives
•
Iterative: Go quickly through all process steps to create a
rough system, then repeat them to improve the system.
Iterative refinement.
•
Sequential: As far as possible, complete each process step
before beginning the next. Waterfall model.
•
Phased: Divide the project into a number of phases.
Implement each phase in turn and put it in production
immediately.
CS 5150
15
Iterative Refinement
Evaluation
Implementation
CS 5150
Requirements
Design
16
Iterative Development: Iterative Refinement
(Evolutionary Development)
Concept: Initial implementation for client and user
evaluation, followed by refinement until system is complete.
• Vaporware: user interface mock-up
• Throw-away software components
• Dummy modules
• Rapid prototyping
• Successive refinement
CS 5150
17
Iterative Processes: Requirements and Risk
Mistakes in the requirements are the most expensive to
correct.
Requirements are hard to understand until there is an operational
system, particularly with user interfaces
Create an outline system quickly, review it with clients, test it
with users, improve the understanding of the requirements
Example: Integration of browser into operational system
CS 5150
18
Sequential Development:
The Waterfall Model
Requirements
Feasibility study
Requirements
Design
System design
Implementation
Program design
Implementation (coding)
Testing
Acceptance & release
Operation & maintenance
CS 5150
19
Discussion of the Waterfall Model
Advantages:
•
•
•
•
Process visibility
Separation of tasks
Quality control at each step
Cost monitoring at each step
Disadvantages:
Each stage in the process reveals new
understanding of the previous stages, which
often requires the earlier stages to be revised.
The Waterfall Model is not enough!
CS 5150
20
Sequence of Processes
A pure sequential model is impossible
Examples:
•
A feasibility study cannot create a proposed budget and
schedule without a preliminary study of the requirements and a
tentative design.
•
Detailed design or implementation usually reveals gaps in the
requirements specification.
The plan must allow for some form of iteration.
CS 5150
21
Modified Waterfall Model
Feasibility study
Waterfall model
with feedback
Requirements
This is better
System design
Program design
Implementation (coding)
Testing
Acceptance & release
Operation & maintenance
CS 5150
22
Phased Development
A simple system with basic functionality is brought quickly
into production (Phase 1).
Subsequent phases are based on experience gained from
users of each previous phase.
Advantages
• Pay-back on investment begins soon.
• Requirement are more clearly understood in developing
subsequent phases.
• User feedback can be incorporated in later phases.
CS 5150
23
Phased Development Online
When software is released online it is possible to divide it
into small phases that are developed and released in quick
succession.
Example: Amazon.com divides most software development
into phases of about four weeks elapsed time.
This approach is excellent for continual enhancement of a
system within an established architecture.
It is not possible for shrink wrapped software, embedded
systems, or similar environments.
CS 5150
24
Mixed Processes: User Interface Development
User interfaces have to be tested with users. This forces
iterative development, even within an underlying
sequential process.
A common model is to combine iterative refinement of user
interfaces within an overall sequential process.
(Iteration within the steps of a sequential process is
sometimes called a spiral development process.)
CS 5150
25
Examples of Mixed Processes:
Iterative Refinement + Waterfall Model:
Problem: Add graphics package to a programming
environment
Phase 1: Iterative refinement
Extend current environment with a preprocessor and run-time
support package. Test with users. Make several new versions until
users are pleased with function. Throw the code away.
Phase 2: Modified waterfall
Use the results of Phase 1 as the basis for a formal set of
requirements. Write new compiler and run-time system
incorporating graphics elements. Make minor adjustments to
requirements as needed.
CS 5150
26
Modern Developments in Software Processes
Changes during the software development process are expensive.
• If the requirements are poorly understood, or expected to
change, select a process that keeps flexibility. Iterative
refinement, phased implementation.
• For big software systems with many inter-related components,
avoid major changes to the design of a system during
development. Sequential process, such as the modified
waterfall model.
CS 5150
27
Modern Developments in Software Processes
Agile software development is a variant of iterative
refinement that stresses rapid iterations with a flexible
approach to requirement and design.
Extreme programming is an approach that concentrates on
selected techniques of software development, e.g., coding
by teams, design and code reviews, and typically releases
software in a sequence of small phases.
CS 5150
28
Observations about Software Processes
Completed projects should have the basic process steps
but ... the development process is always partly evolutionary.
Risk is lowered by:
• Prototyping key components
• Dividing into phases
• Following a visible software process
• Making use of reusable components
Conclusion
It is not possible to complete each step and throw it over the wall.
CS 5150
29
CS 5150 Project Presentations: Iterative Option
Evaluation
Requirements
first presentation
second presentation
third presentation
Implementation
CS 5150
Design
30
CS 5150 Project Presentations: Sequential Option
1. Requirements
Feasibility study
Requirements
2. Design
System design
Program design
3. Implementation
Implementation (coding)
If you follow a
sequential process the
three presentations
should be as shown.
CS 5150
Testing
Acceptance & release
Operation & maintenance
31
CS 5150
Software Engineering
Project Suggestions
CS 5150
32
Project Suggestion: eCommons
Harvesting from Web sites for the Cornell
academic repository
John Saylor, Cornell University Library
CS 5150
33
Project Suggestion:
iPhone Application for Pet Nutrition
Stephanie Specchio, College of Veterinary Medicine
Ron DiNapoli, Cornell Information Technologies
CS 5150
34
Project Suggestion: Field of Mars
Social networking and e-commerce site for athletics
and fitness
Jonathan and Aleda Schaffer
Johnson School, Cornell University
CS 5150
35
Project Concept: Legal Information Institute
• Spaeth database of
Supreme Court statistics
• User contributed
queries
Tom Bruce, Director
Legal Information
Institute
CS 5150
36
Project Concept:
FSAE Race Car
Controller area network for FSAE race car
Cangming Liu
FSAE Race Team
CS 5150
37
Project Concept:
Risk Management and Public Safety
Personal Protection Equipment & Training
Assessment Tool
Curtis Baker, Risk Management and Public Safety
Information Services [former CS 5150 student]
CS 5150
38
Project Suggestion: Civitas electronic voting system
Civitas electronic voting system
Michael Clarkson
Computer Science Department
CS 5150
39
Project Suggestions from Electrical and
Computer Engineering
GPS Sensor Array Management
Brady O'Hanlon
Aerobic Exercise Monitor
John Belina
CS 5150
40
Project Suggestion: SNAP
Social Network Applied Perception (SNAP) Search
Engine
Stephen Purpura, Cornell Information Science
CS 5150
41