1. CS 5150 Software Engineering
Lecture 4
Software Processes 3

2. Administration Projects Announcements by project groups
• Roll call of projects and team numbers
• Who does not have a project team?

3. Administration Project teams:
• If you do not have a team, please meet after class.
• If you are still having difficulty finding a team send to the course team
• We may ask teams to add extra members
• If you have definitely chosen a project and reached agreement with your client, send to the course team with the names of your team members

4. Administration Test 1 See the Tests page on the web site.
Monday, September 12 at 7:30 p.m. in Phillips Hall 101.
Two questions on material that has been covered in the lectures, including the class on the day of the test.
Open book. You may bring any books or notes.
Laptops can be used to store copies of the course materials and notes, but for no activity that involves networking.
If you miss a test, there is no opportunity to retake it.

5. Sequential Development: The Waterfall Model
Requirements
Feasibility study
Requirements
Design
System design
Implementation
Program design
Implementation (coding)
Testing
Acceptance & release
Operation & maintenance

6. Iterative Refinement
Evaluation
Requirements
Design
Implementation

7. Incremental Development (Sprints)
For each increment (sprint) a team works through a full software development cycle including planning, requirements analysis, design, coding, unit testing, and acceptance testing.
Each sprint is completed in a fixed time period, e.g., four weeks.
The size of an sprint is based on team size, e.g., 5-10 people.
Sprint 1
Sprint 2
Sprint 3
Accept Sprint 1
Accept Sprint 2
Accept Sprint 3

8. 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!

9. 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 and implementation reveal gaps in the requirements specification.
• Requirements and available technology change with time.
The plan must allow for some form of iteration.

10. Modified Waterfall Model
Feasibility study
Waterfall model with feedback
This is better
Requirements
System design
Program design
Implementation (coding)
Testing
Acceptance & release
Operation & maintenance

11. Discussion of Iterative Refinement
Concept: Initial implementation for client and user evaluation, but not for release, followed by refinement until system is complete.
• User interface mock-up
• Throw-away software components
• Dummy modules
• Rapid prototyping
• Successive refinement

12. 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: Start-up time of launching a complex application.

13. Incremental Development (Sprints): Discussion
A simple system with basic functionality is brought quickly into production. Subsequent sprints are based on experience gained from users of each previous release.
Advantages
Pay-back on investment begins soon.
Requirement are more clearly understood in developing
subsequent sprints – minimize waste.
• User feedback can be incorporated in later phases.
Challenge
A high-level team must establish overall architecture and coordinate increments

14. Incremental Development of Online Systems
When software is released online it is possible to divide it into small increments that are developed and released in quick succession.
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.

15. Mixed Processes
In practice, many large projects create a process that is suitable for the specific development. For example:
• A system may use a sequential process with iteration within the individual process steps. This is sometimes called a spiral development process.
• User interfaces have to be tested with users. This forces iterative development, even within an underlying sequential process.
• A phase 1 system may be developed by iteration and used as requirements for a phase 2, which is developed sequentially.

16. 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.

17. Corporate Processes
Large software development organizations have their own internal processes that are designed for their needs. For example:
• Amazon.com (Internet commerce) divides most software development into phases of about four weeks elapsed time.
• Lockheed Martin (government contactor) follows a process that fits with the way that the US government manages software contracts.
• SAP (business software) emphasizes the functionality that is seen by their business customers.
• Microsoft (PC software) places great emphasis on testing with a very wide variety of equipment and backward compatibility.

18. 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, sprints, 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.
• If the market for the software is poorly understood, use an incremental process that gets operational software in front of customers as quickly as possible.

19. 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
• Frequent releases, dividing large projects into phases
• Early and repeated testing with users and customers.
• Following a visible software process
• Making use of reusable components

20. CS 5150 Project Presentations: Iterative Option
Evaluation
Requirements
first presentation
second presentation
third presentation
Implementation
Design

21. CS 5150 Project Presentations: Sequential Option
1. Requirements
Feasibility study
Requirements
2. Design
System design
Program design
3. Implementation
Implementation (coding)
Testing
If you follow a sequential process the three presentations should be as shown.
Acceptance & release
Operation & maintenance

22. CS 5150 Project Presentations: Incremental Development
Sprint 1
Sprint 2
Sprint 3
First release
Second release
Third release
first presentation
second presentation
third presentation