Re: JESS: Naming facts

[Alan Moore]

You could also try something like the following:

WARNING: not real code...
file: DeviceMonitor.jess

(import com.yourpackage.Device)
(defclass Device com.yourpackage.Device)

(defrule shutdown-out-of-limit-devices
   (Device (outOfLimit TRUE) (id ?deviceId) (OBJECT ?obj))
=>
   (printout t "Device " ?deviceId " is out of limit")
   (printout t "Shutting it down now...")
   (?obj shutdown)
)


file: Device.java

import java.beans.*;

public class Device
{
   private boolean outOfLimit = false;
   private java.beans.PropertyChangeSupport pcs = new 
PropertyChangeSupport(this); // or somthing...

   public Device( String deviceId )
   {
      this.deviceId = deviceId;
      pollDeviceStatus();
   }

   public String getId() { return deviceId; }

   public void shutdown() { /* whatever... */ }

   public void setOutOfLimit( boolean outOfLimit )
   {
      boolean oldValue = this.outOfLimit;
      this.outOfLimit = outOfLimit;
      pcs.firePropertyChangeEvent( "outOfLimit", new Boolean(oldValue), 
new Boolean(outOfLimit));
   }

   public boolean isOutOfLimit() { return isOutOfLimit; }

   public void pollDeviceStatus()
   {
      // get actual device status from serial port, USB, net, etc.
      boolean newStatus = getDeviceActualStatus(); // TBD
      boolean prevStatus = device.isOutOfLimit();

      if ( newStatus != prevStatus ) // prevent redundant changes
         device.setOutOfLimit( newStatus );
   }
}

file: Main.java

import jess.*;

public class Main
{
   private HashMap devices = new HashMap();

   private void createDeviceProxies()
   {
      // populate devices hashmap with your devices
      // e.g. Device device = new Device("device id 1");
      // devices.put("device id 1", device);
   }

   static public void main( String[] args )
   {
      createDeviceProxies();

      Rete rete = new Rete();
      Jesp parser = new Jesp( ... ); // plus, load your rules, etc
      // be sure your jess script does defclass for your "Device" class
      rete.reset();

      for ( Device device : devices )
      {
         rete.definstance("Device", device, true );
      }

      while ( true )
      {
         for ( Device device : devices )
         {
            device.pollDeviceStatus();
         }

         // now all devices are updated, reason about what to do
         rete.run();

         // since we are polling, rest for a while
         try { Thread.sleep(1000); } catch Exception /// blah blah blah
      }
   }
}

Of course, if your devices can supply asynchronous event notifications 
you wouldn't have to do the polling as shown above - you'd simply call 
rete.runUntilHalt() in your main method and let your Device objects 
update themselves via the event handlers.

Hope this helps.

Alan



Donnelly wrote:
Given a list of device names, when a device is out of limits I want to
assert an appropriately named fact
   devicename-exceeds-limits.
If I use (assert (sym-cat ?device ?condition))  the fact becomes
  sym-cat devicename -exceeds-limits.
How can I create correctly named facts?

Stephen Donnelly

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