Reference &
User Manual
    RTXPS  On-line Reference Manual

      Release Level 2.0
      Release Date 2012 06
      Revision Level 1.0
    Last modified on:   Sunday, 12-Aug-12 20:51 CEST

    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.

    Data base structure

      mysql> describe descriptors;
      FieldTypeNull Key Default Description
      id int(11)NO PRINULLauto_increment
      name varchar(255)YES NULL internal name, must not be changed once referenced
      display_name varchar(64) YES NULL arbitrary name for display e.g., in different languages
      type varchar(255) YES NULL S = symbolic, H = hybrid, V = variable (free text)
      unit varchar(255) YES NULL unit of measurement where applicable
      def_value varchar(255) YES NULL default value
      desc textYES NULL description text for the header meta field
      owner varchar(32) YES NULL
      createddatetime YES 0000-00-00 00:00:00
      modified datetime YES 0000-00-00 00:00:00 timestamp of the last modification, see change log table below
      url varchar(255) YES NULL
      format varchar(16) YES NULL display format for numerical values, C syntax
      sort varchar(20) YES NULL sorting of the symbolic values by numerical ranges, ascending or descending

      mysql> describe desc_range;
      FieldTypeNullKey DefaultDescription
      id int(11) YES MUL NULL
      desc_from float YES NULL lower value for the range
      desc_to float YES NULL upper value for the range
      desc_median float YES NULL explicit median, used as default for the symbolic reference; if unspecified the arithmetic mean of the desc_from - desc_to values is used
      seq int(11) YES NULL drives explicit sequencing of symbols/ranges
      desc_range varchar(255) YES NULL symbolic label for a range

      mysql> describe desc_questions;
      FieldTypeNullKey DefaultDescription
      id int(11) YES MUL NULL
      question varchar(255) YES NULL text (htlm) of the explanatory questions shown in the editor
      seq int(11) YES NULL

      The current descriptor value is saved in a standard triple column table like:

      FieldTypeNullKey DefaultDescription
      ID int(10) unsigned NO PRI 0
      DESCRIPTOR varchar(32) NO PRI
      VALUE varchar(255) NO depending on the display function used, value is shown as string (symbolic) or float

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