Problems and Frames IV Heuristics

Heuristics? Serving or helping to find out or discover; Guidelines; But connotations of trial and error.

Heuristics Principal steps: –Identify the core problem –Identify the ancillary problems –Standard decompositions of sub problems –Identify concerns and difficulties

More heuristics Different tempi More than two moods Complex domain or requirement Modelling the user

Different tempi When one part of your problem is in a slow tempo and one in a fast tempo, treat them as different sub problems. Look at Tennis Court Lights handout What are the different tempi?

More than two moods Every frame has at least 1 description (of domain properties) in the indicative mood And at least two (req. and spec.) in the optative mood. Sometimes you need 3 moods which indicates presence of at least two subproblems Look at Air Traffic Control

Complex domain or environment In each basic frame a clear expectation of relative complexities of the domains and requirement complexity –Req. Beh. Frame: controlled domain may be complex, but you expect the requirement to be satisfiable by simple control law. –Commanded Beh. Frame: Controlled domain complex, but controller simple.

Continued –Info. Display Frame: RW complex, display domain quite simple. Req. = simple relationship between req and specification phenomena of RW –Workpieces: w/pieces may be complex, user domain simple –Transformation: inputs & outputs of roughly equal complexity. I/O relation satisfiable by traversal of both domains

Continued An unusually complex domain indicates a possible further decomposition Package router: core problem was Required Behaviour. –Complexity = destinations not available to sensors, so introduce a model domain = new subproblem

Modelling user In workpieces frame, user domain is unstructured stream of commands Where user domain is of interest for its own sake, this indicates a subproblem –If we need to know who edited a workpiece, we need a model of each user to record individual editing activities. This is a separate problem

Exercises What are the different tempi in the Home Heating Control problem? What are the moods in the Package Router problem? What are the subproblems in the University Administration system?