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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.extractors;
import jadex.commons.SUtil;
import jadex.rules.rulesystem.rete.Tuple;
import jadex.rules.rulesystem.rete.nodes.VirtualFact;
import jadex.rules.state.IOAVState;
import jadex.rules.state.OAVAttributeType;
/**
* Extractor for an attribute value (or the whole object).
*/
public class ObjectExtractor implements IValueExtractor
{
//-------- attributes --------
/** The attribute type. */
protected OAVAttributeType attr;
/** The key value. */
protected Object key;
//-------- constructors --------
/**
* Create a new extractor.
*/
public ObjectExtractor(OAVAttributeType attr)
{
this.attr = attr;
}
/**
* Create a new extractor.
*/
public ObjectExtractor(OAVAttributeType attr, Object key)
{
this.attr = attr;
this.key = key;
}
//-------- methods --------
/**
* Get the value of an attribute from an object or tuple.
* @param left The left input tuple.
* @param right The right input object.
* @param prefix The prefix input object (last value from previous extractor in a chain).
* @param state The working memory.
*/
public Object getValue(Tuple left, Object right, Object prefix, IOAVState state)
{
// Fetch the value from the state
// a) attr == null -> use object
// b) attr !=null -> use state.getAttributeValue(object, attr) or
// state.getAttributeValues(object, attr);
if(right instanceof VirtualFact)
right = ((VirtualFact)right).getObject();
Object ret;
if(attr==OAVAttributeType.OBJECTTYPE)
{
ret = state.getType(right);
}
else
{
ret = attr==null? right:
OAVAttributeType.NONE.equals(attr.getMultiplicity())?
state.getAttributeValue(right, attr):
key!=null? state.getAttributeValue(right, attr, key):
state.getAttributeValues(right, attr);
}
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 tupleindex==-1 && SUtil.equals(this.attr, attr);
}
/**
* Get the set of relevant attribute types.
*/
public AttributeSet getRelevantAttributes()
{
AttributeSet ret = new AttributeSet();
if(attr!=null)
ret.addAttribute(attr);
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()
{
return AttributeSet.EMPTY_ATTRIBUTESET;
}
/**
* Get the attribute.
* @return The attribute.
*/
public OAVAttributeType getAttribute()
{
return attr;
}
/**
* Get the string representation.
* @return The string representation.
*/
public String toString()
{
return ""+(attr==null? "object": attr.getName())+(key==null? "": "["+key+"]");
}
/**
* The hash code.
*/
public int hashCode()
{
return 31 + (attr!=null ? attr.hashCode() : 0);
}
/**
* Test for equality.
*/
public boolean equals(Object obj)
{
if(this==obj)
return true;
return obj instanceof ObjectExtractor
&& SUtil.equals(attr, ((ObjectExtractor)obj).getAttribute());
}
}