Questions, Options, and Criteria: Elements of design space analysis
QOC - Questions, Options, and Criteria - originated as a semiformal notation for a design rationale, intended to make it easier to discuss the tradeoffs made in choosing a design.
The Q, O, and C, of the title indicate the three most basic concepts of Design Space Analysis:
- Questions - "key issues for structuring the space of alternatives"
- Options - possible alternatives
- Criteria - the bases for choosing among the options
A fourth concept is also needed:
- Assessments - whether an option supports or challenges a criterion.
A QOC diagram indicates short descriptions (preceded by Q: O: or C:).Assessments are shown as solid (positive) or dashed (negative) lines between an Option and a Criterion.
Related work is IBIS, gIBIS, Procedural Hierarchy of Issues (1986), and the Decision Representation Language (Lee & Lai 1991). The authors distinguish QOC by IBIS in that QOC is specific to design rationale. They also "see a QOC representation as a condensation of an IBIS-encoded history that brings out the most important elements of the history for logical argumentation." Thus, a discussion in IBIS could be further processed, under this methodology, to identify areas that need further examination.
- Questions are intended to provide a structure for exploring and explaining the options, whereas IBIS' Issues are general, and can be about any topic under discussion.
- Criteria can be made after reflection, whereas (in the authors' mind) IBIS' Arguments are intended to capture discussion on the fly, and may therefore be "less coherent and succinct".
The paper also gives a case study with QOC diagrams based on a user study, and discusses the criteria of QOC, for instance that it is a coproduct of the design process.