Design Rationale

Chapter 26

Brian Barrios

Alistair Nicol

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.

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.

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.

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.