Node Reduction using an Expert System
Definition Of Facts
In the expert system, the node reduction engine sets variables called facts through a process
called assertion. Patterns then evaluate whether facts are satisfied. The list of facts asserted by
the node reduction engine, which are available for use in the rules, are:
| Node |
Facility |
| Name |
Name |
| Modeling Parameters That |
Are Industry Specific |
| Modeling Parameters That |
Are Industry Specific |
| Valence Length |
Parent Facility Distance from Source |
| List of Children Facilities Load |
Load |
Node
The Name is the unique identifier of the node being checked.
The Modeling Parameters That Are Industry Specific are any facts, which the rules need in
order to determine whether the node can be reduced. (Examples are flow or pressure for a gas
system.)
The Valence is the number of facilities connected to the node.
The Parent Facility the name of the up stream facility if the network is radial.
The List of Children Facilities is the list of facilities that are attached to the node. If the system
is a radial system, these are the facilities that are downstream of the node.
The Load is the system load attached to the node.
Facilities
The Name is the unique identifier of the facility.
The Modeling Parameters That Are Industry Specific are any facts, which the rules need in
order to determine whether the node can be reduced. (Examples are pipe diameter, roughness, or
material for a gas system; conductor name, phasing, or spacing for an electrical system.)
The Load is the system load attached to the facility.
Engine Operation
The node reduction engine is made up of two parts: a topological network engine and the rule
based expert system. In order to reduce the facility data, the data needs to be arranged in a
parent-child connectivity model. In other words, each facility needs to know the facilities that
are upstream and downstream from it. Most GIS's support a facility-node based connectivity
model, but if the GIS does not support that connectivity model, it can be built based upon the
coordinates of the facilities.
The node reduction engine takes the GIS data and feeds it into the network engine. The network
engine transforms the facility-node based data into a parent-child model that is stored in
memory.
At this point the node reduction engine uses the network engine to walk the model, asserting
facts from the GIS data for each node. As the node reduction engine visits each node, it calls the
expert system to determine whether the node can be reduced or not. The expert system returns
TRUE or FALSE based upon the evaluation of the rules.
If the expert system returns TRUE, the node reduction engine then removes the node from the
data turning the node into vertices of the new facility. If the expert system returns FALSE, the
node is left in memory.
Once the node reduction engine has finished processing the data, it is either re-imported into the
GIS for use there or exported to the engineering modeling software.
Summary
Node reduction is a vital part of any GIS to Engineering Modeling integration effort. Creating a
piece of "open" and "customizable" software is the best solution. It allows the utility to maintain
the corporate record of their facilities using their GIS and leveraging the data for use in their
engineering modeling software. It also gives the utility the opportunity to produce consistent
skeletons of their GIS data with minimal human intervention.
