Siniša Kolarić, Ph.D.

Siniša is a researcher, IT expert and author focused on advancing design inquiry, practice and technology.

December 22, 2021

The concepts of well-defined and ill-defined problems are of fundamental importance in design research. This is because most non-trivial design problems belong to the class of ill-defined problems.

Well-Defined Problems

Simon (1977) formulated a list of six requirements that a problem must satisfy in order to be considered a well-structured one:

  • Objective solution tests exist.
  • A problem space (set of states) exists for the problem.
  • Transitions between states can be represented in the problem space.
  • New knowledge can be represented.
  • If the problem solver acts in a physical world, a problem space for the physical world exists as well.
  • All five precedings items are practically computable.

Well-defined problems are also called “tame” because they are structured in advance. Here, “structured” means that all its constituent states and feasible solving strategies are known in advance.

Ill-Defined Problems

“Ill-defined” problems are now defined simply as a residual of well-defined problems. That is, we say that a problem is ill-defined when it is not well-defined. For a readable introduction into this topic, see Simon (1977).

Comparison

The following table (Raymond, 1990) provides an informative side-by-side comparison of well-defined and ill-defined problems.

  Well-defined problems Ill-defined problems
Problem specification: complete, unambiguous incomplete, ambiguous
Solution evaluations: definite criteria no definite criteria (i.e., no stopping rule)
Knowledge utilized: represented in one or more problem spaces (in advance of problem solving) many sources (i.e., problem spaces) that cannot be determined in advance and need to be integrated
Operators: enumerable and all known in advance no exhaustive, enumerable set
Solution path: exists and is predetermined (but has to be found) no predetermined solution path exists
Examples: chess, theorem-proving design, planning, document composition

References

  • Herbert A Simon. The structure of ill-structured problems. In Models of discovery, pages 304–325. Springer (1977).

  • Raymonde Guindon, Knowledge exploited by experts during software system design, International Journal of Man-Machine Studies, 33(3):279–304, 1990.

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