Changing Facts — Backward-Chaining Rules

Backward-chaining rules define how values for descriptors are affected by values of other descriptors, data entry, or results from a simulation model. Backward-chaining rules can result in the assigmnent of descriptor values or can define their relative or incremental changes. Additionally, rules can include basic calculations and can control the inference strategy for a given context. An example for a rule is as follows  

The rules uses two descriptors (average reservoir depth and retention time) to evaluate them in either text format (small) or numerical format ( 30). If both conditions are true, a new descriptor value is set. 

Another use of the backward-chaining capabilities of RTXPS is to provide few summarized variables to describe large scenarios that would usually generate large data volumes. The scenario can be reduced to selected facts that are relevant for describing the event, such as level of exposure, contamination area, number of people involved, or a hazard classification of the event. These values are then used to trigger the appropriate actions. 

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