Building a theory of problem solving and scientific discovery: How big is N in N-space search?

The framework developed by Newell and Simon (1972) of problem solving as a search of a problem space, provides core concepts (e.g., representations, operators, heuristics, task analyses, etc.) that are used by many researchers studying complex tasks from the point of view of artificial intelligence, psychology, Human-Computer Interaction, and education. However, in recent years some researchers have tried to push beyond seeing tasks as search of a single problem space, and have instead suggested that many tasks can be better treated as a N-space search.