Shared Tools:  Reference Manual
    Release Level 5.4 Release Date 2008 10 Revision Level 1.0
Last modified on:   Monday, 2-Nov-09 08:38 CET

XPS: backward-chaining rule-based expert system


The facts (data) of expert systems XPS and RTXPS are stored in DESCRIPTORs.

A value is assigned to a DESCRIPTOR either by direct editing or by starting the rule-based inference, that will recursively compile information from the data base including asking the user where necessary, to assign a value to the target (Descriptor) of the inference.

The system then uses a set of alternative methods enumerated in the DESCRIPTOR definition to obtain or update the DESCRIPTOR value in the current context. The inference engine compiles all necessary information for the appropriate Backward Chaining Rules' input conditions recursively, evaluates the Backward Chaining Rules, and eventually updates the target DESCRIPTOR.

Descriptor syntax and descriptions

Descriptors are defined in terms of:
  • an internal name used by the code, not to be changed
  • a DISPLAY NAME freely changeable by the user;
  • a UNIT (text string)
  • A TYPE. Currently supported types:
    • V (variable, text only values),
    • H (hybrid): numerical ranges and associated symbolic range;
    • S (symbolic): list of symbols only.
  • META DATA: user, modification date, explanatory text.
  • TABLE of legal value ranges (type dependent); The legal range is defined from the lower bound of the first to the upper bound of the last range.
    The range definitions include triplest of numbers
      minimim - median (display) - maximum values, followed by a symbolic description of the range.
    Range definitions must be contiguous; the upper bound of the lower rangte must be identical to the lower bound of the following range. Median (display default) values are optional, but must be between (including) the upper and lower bounds for the range If no median value is defined the arithmetic mean is used.

  • Question: HTML style text that is shown in the Descriptor editor.

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