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Jadex Rules is a small lightweight rule engine, which currently
employs the well-known Rete algorithm for highly efficient rule
matching. Jadex rules is therefore similar to other rule engines
like JESS and Drools. Despite the similarities there are also
important differences between these systems:
* Jadex Rules is very small and
intended to be used as component
of other software. Even though rules can be specified in a Java
dialect as well as (a small variation of) the CLIPS language
its primary usage is on the API level. Jadex Rules is currently
the core component of the Jadex BDI reasoning engine.
* Jadex Rules cleanly separates between state and rule representation.
This allows the state implementation as well as the matcher to be
flexibly exchanged. Some experiments have e.g. been conducted with
a Jena representation. Regarding the matcher, it is planned to
support also the Treat algorithm, which has a lower memory footprint
than Rete.
* Jadex Rules pays close attention to rule debugging. The state as
well as the rete engine can be observed at runtime. The rule debugger
provides functionalities to execute a rule program stepwise and also
use rule breakpoints to stop the execution at those points.
package jadex.rules.rulesystem.rete.constraints;
import jadex.commons.SUtil;
import jadex.rules.rulesystem.rete.Tuple;
import jadex.rules.rulesystem.rete.extractors.AttributeSet;
import jadex.rules.rulesystem.rete.extractors.IValueExtractor;
import jadex.rules.rulesystem.rules.ILazyValue;
import jadex.rules.rulesystem.rules.IOperator;
import jadex.rules.state.IOAVState;
import jadex.rules.state.OAVAttributeType;
/**
* A constraint evaluator is responsible for evaluating constraints.
* It operates on an operator and two extractors. It uses the extractors
* to fetch the values and invokes the operator subsequently with the
* values.
*/
public class ConstraintEvaluator implements IConstraintEvaluator
{
//-------- attributes --------
/** The operator. */
protected IOperator operator;
/** The value extractor 1. */
protected IValueExtractor extractor1;
/** The value extractor 2. */
protected IValueExtractor extractor2;
//-------- constructors --------
/**
* Create a new constraint evaluator.
* @param operator The operator.
* @param extractor1 The first extractor.
* @param extractor2 The second extractor.
*/
public ConstraintEvaluator(IOperator operator, IValueExtractor extractor1, IValueExtractor extractor2)
{
assert operator!=null;
assert extractor1!=null;
assert extractor2!=null;
this.operator = operator;
this.extractor1 = extractor1;
this.extractor2 = extractor2;
}
//-------- methods --------
/**
* Evaluate the constraints given the right object, left tuple
* (null for alpha nodes) and the state.
* @param right The right input object.
* @param left The left input tuple.
* @param state The working memory.
*/
public boolean evaluate(final Object right, final Tuple left, final IOAVState state)
{
boolean ret = false;
try
{
ILazyValue val1 = new ILazyValue()
{
public Object getValue()
{
return extractor1.getValue(left, right, null, state);
}
};
ILazyValue val2 = new ILazyValue()
{
public Object getValue()
{
return extractor2.getValue(left, right, null, state);
}
};
ret = operator.evaluate(state, val1, val2);
// System.out.println(toString()+" "+ret);//+" "+extractor1.getValue(left, right, state)+" "+extractor2.getValue(left, right, state));
}
catch(Exception e)
{
// Catch extractor exception and return false in this case.
System.out.println("eval error: "+this);
e.printStackTrace();
}
return ret;
}
/**
* Test if a constraint evaluator is affected from a
* change of a certain attribute.
* @param tupleindex The tuple index.
* @param attr The attribute.
* @return True, if affected.
*/
public boolean isAffected(int tupleindex, OAVAttributeType attr)
{
return extractor1.isAffected(tupleindex, attr)
|| extractor2.isAffected(tupleindex, attr);
}
/**
* Get the set of relevant attribute types.
*/
public AttributeSet getRelevantAttributes()
{
AttributeSet ret = new AttributeSet();
ret.addAll(extractor1.getRelevantAttributes());
ret.addAll(extractor2.getRelevantAttributes());
return ret;
}
/**
* Get the set of indirect attribute types.
* I.e. attributes of objects, which are not part of an object conditions
* (e.g. for chained extractors)
* @return The relevant attribute types.
*/
public AttributeSet getIndirectAttributes()
{
AttributeSet ret = new AttributeSet();
ret.addAll(extractor1.getIndirectAttributes());
ret.addAll(extractor2.getIndirectAttributes());
return ret;
}
/**
* Get the string representation.
* @return The string representation.
*/
public String toString()
{
return extractor1+" "+operator+" "+extractor2;
}
/**
* Get the operator.
*/
public IOperator getOperator()
{
return operator;
}
/**
* Get the first value extractor.
*/
public IValueExtractor getExtractor1()
{
return extractor1;
}
/**
* Get the second value extractor.
*/
public IValueExtractor getExtractor2()
{
return extractor2;
}
/**
* Get the hash code.
*/
public int hashCode()
{
int result = 31 + ((extractor1 == null) ? 0 : extractor1.hashCode());
result = 31 * result + ((extractor2 == null) ? 0 : extractor2.hashCode());
result = 31 * result + ((operator == null) ? 0 : operator.hashCode());
return result;
}
/**
* Test if the evaluator equals an object.
*/
public boolean equals(Object obj)
{
if(this==obj)
return true;
boolean ret = false;
if(obj instanceof ConstraintEvaluator)
{
ConstraintEvaluator other = (ConstraintEvaluator)obj;
ret = SUtil.equals(extractor1, other.getExtractor1())
&& SUtil.equals(extractor2, other.getExtractor2())
&& SUtil.equals(operator, other.getOperator());
}
return ret;
}
}