Design Rationale

1. Design Rationale Chapter 26 Brian Barrios Alistair Nicol

2. IBIS • IBIS (Issued-Based Information Systems) • Technique which was devised in order to capture design process itself. • Considering the pros and cons of alternative answers to questions. • Questions called issues and answers are called positions • The pros and cons are called arguments • Problems: • Dependencies between issues were not catered for: that is, no account was taken of whether the answer to one questions relied on the answer to another. • Only questions which become issues, that is, which are deliberated, are represented on the issue map.

3. Design space analysis • Explorations of the space of alternatives. • Explore alternatives that fulfill the system's specifications. • Hopefully the designer is forced to explore many different options to make the end result better. • QOC (Questions, Options and Criteria) • Also uses questions and answers idea. • Specifically for design instead for general questions in IBIS • Recording Design decisions are time consuming and expensive. • However, though tough to maintain, does result in a thorough coverage of important design issues, and perhaps the advent of appropriate software support tools will support designers using the technique.

4. Claims analysis • A claim relates some aspect of a system’s design with an important consequence for the user. • Done by creating scenarios of the system’s use and analyzing them for claims.

5. Summary. • Design decisions need to be recorded and communicated to many different people. • Documentation is an inappropriate way to communicate design information to users • Documenting design rationale is a time-consuming process • Design space analysis encourages designers to explore more alternatives • Claims analysis concentrates on refining one design.