11425 Software Engineering

1. 11425 Software Engineering Coping With Change February 23, 2012 Sommerville, I., Software Engineering, Pearson, 9th Ed., 2010.

2. Overview • Change avoidance • Change tolerance • Prototyping • Incremental delivery

3. Coping With Change • Change is inevitable in all large software projects • Business changes lead to new and changed system requirements • New technologies open up new possibilities for improving implementations • Changing platforms require application changes • Work that has been completed has to be redone. This is called rework. • There are two related approaches that may be used to reduce the costs of rework: • Change avoidance • Change tolerance

4. Change Avoidance • The software process includes activities that can anticipate possible changes before significant rework is required • For example, users experiment with a prototype before committing to high software production costs

5. Change Tolerance • The software process is designed so that changes can be accommodated at relatively low cost • This normally involves some form of incremental development

6. Coping with Change • There are two ways of coping with change and changing system requirements: • System prototyping • Incremental delivery

7. System Prototyping • A prototype is an initial version of a software system that is used to: • demonstrate concepts, • try out design options, • and find out more about the problem and its possible solutions • A prototype can be help with the elicitation and validation of system requirements • Prototypes do not have to be executable to be useful

8. System Prototyping • A prototype can be used to explore particular software solutions and to support user interface design • Prototyping supports change avoidance. • May involve leaving out functionality • Prototype should focus on areas of the product that are not well-understood; • Error checking and recovery may not be included in the prototype; • Focus on functional rather than non-functional requirements such as reliability and security

9. Process of Prototype Development

10. Throw-away Prototypes • Prototypes should be discarded after development as they are not a good basis for a production system: • It may be impossible to tune the system to meet non-functional requirements • Prototypes are normally undocumented • The prototype structure is usually degraded through rapid change • The prototype probably will not meet normal organizational quality standards

11. Incremental Delivery • Incremental delivery is an approach to software development where some of the developed increments are delivered to the customer and deployed for use in an operational environment. • Advantages: • Customers can use the early increments as prototypes and gain experience. • Customers do not have to wait until the entire system is delivered before they can gain value from it. • Supports coping with changes • The most important system services receive the most testing

12. Incremental Delivery • Problems: • Most systems require a set of basic facilities that are used by different parts of the system • Iterative development can also be difficult when a replacement system is being developed • There is no complete system specification until the final increment is specified

13. Incremental Delivery

14. Homework Assignment #1 • From the Textbook, page 54: • 2.1 • 2.4 • 2.7 • Due: Thursday March 1, 2012 by email (PDF) to: m.muhanna@psut.edu.jo