Descriptor files

Descriptors are a shared, global data resources that is available throught an entire application through a pointer to the Knowledge base.

A Descriptor has a range or set of legal values; the objective of the expert system backwards-chaining inference procedure is to dertermine the current value of this target Descriptor in a given context, defined by the current values of other Descriptors, database values, GIS attributes, return values from built-in functions, or model results.

Descriptors

The complete syntax of a Descriptor is:

       DESCRIPTOR
       <descriptor_name>
       A  <alias_for_descriptor_name>
       T  <descriptor_type>
       U  <unit>
       V  <range> / <range> / <range> / ...
       R  <rule#> / <rule#> / ...
       TB <table#> / <table#> / ...
       F  <function>
       IF <interface function>
       G  <gis_function> <gis_overlay>
       Q  <question>
       MODEL
       <model_name>
       T <model_type>
       I <input_descriptor> / <input_descriptor> /
       O <output_descriptor> / <output_descriptor> /
       ENDMODEL
       ALTERNATIVE
       <alternative>
       <alternative defs>
       ENDALTERNATIVE
       LAYOUT
       X <window x-coordinate>
       Y <window y-coordinate>
       WIDTH <window width>
       HEIGHT <window height>
       BGCOLOR <window bgcolor>
       BORDER_WIDTH <window borderwidth>
       BORDER_COLOR <window bordercolor>
       FORMAT <value selector format_string>
       DELTA <value selector increment>
       HYPER_INFO <hyperinfo path> 
       HYPER_X <hyperinfo x-coordinate>
       HYPER_Y <hyperinfo x-coordinate>
       HYPER_WIDTH <hyperinfo width>
       HYPER_HEIGHT <hyperinfo height>
       HYPER_TWIDTH <hyperinfo backgroundwin width>
       HYPER_THEIGHT <hyperinfo backgroundwin height>
       HYPER_FGCOLOR <hyperinfo foreground color>
       HYPER_BGCOLOR <hyperinfo background color>
       HYPER_KEYCOLOR <hyperinfo keyword color>
       HYPER_HIKEYCOLOR <hyperinfo highlight color>
       HYPER_SWBORDERC <hyperinfo border color>
       ENDLAYOUT
       ENDDESCRIPTOR

Descriptors in RTXPS (forward chaining)

Within the context of forward chaining RTRULES, there is currently only a subset of the complete descriptor syntax and associated functionality implemented:

 DESCRIPTOR
       <descriptor_name>
       A  <alias_for_descriptor_name>
       T  <descriptor_type>
       U  <unit>
       V  <range> / <range> / <range> / ...
       D  <default>
       Q  <question>
       LAYOUT
        .....
       ENDLAYOUT
 ENDDESCRIPTOR

Typical examples of a symbolic and a hybrid Descriptor definition would be:

   DESCRIPTOR
   emergency_type
   T S
   V toxic_spill / explosion / chemical_fire / forest_fire /
   V flood / landslide / earthquake /
   Q What is the type of this emergency ? \nl
   Q Please select the most appropriate choice from the list.
   ENDDESCRIPTOR

   DESCRIPTOR
   max_amount
   T S
   U kg
   V extremely_small [    0,    10,    20] /
   V small           [   20,   100,   200] /
   V medium          [  200,  1000,  2000] /
   V large           [ 2000, 10000, 20000] /
   V very_large      [20000, 50000,100000] /
   D 2000
   Q What is the amount of hazardous substance involved in this
   Q accident ?
   LAYOUT
   FORMAT %8.0f
   DELTA 1.0
   ENDLAYOUT
   ENDDESCRIPTOR

For the forward chaining system, a special type of Descriptor has been added:

   DESCRIPTOR
      date
      T variable
   ENDDESCRIPTOR

   DESCRIPTOR
      CAS_Number
      T variable
   ENDDESCRIPTOR

The variable Descriptor type is used to give the expert systems access to Variables for which no legal range can be enumerated easily; examples are date, a chemical or place name, or the CAS number of a chemical. While the range or set of legal values is, in principle, known, it may simply be too large to conveniently present to the user for choice with the standard expert system editor tool. The variable descriptor are set or defined with other, specific tools in the system.