Personally I don't like the idea of a Map as a model as it has no type, so straight away you lose object level descrimination. Also a Map is not declarative in defining what it is you are reasoning over. It's a hack to get over the limitations of the current environment.

In the engine we have something called FactTemplats, which we do not currently document - it's a hidden feature. These work much less Jess Deftemplates, and where infact made so that we could support a Jess/clips. The implementation is basically an array and uses name tokenising to get access. i.e. you write person.name == "Godmar" and we rewrite it as person.setField( 0, "Godmar" ). Although we haven't yet got the rewritting part done so currently you have to manually do the above, or make it lookup the position each time with person.setField( "name", "Godmar" ). These FactTemplates can be reasoned over in the LHS just like pojos.

However I'm not currently happy with the solution and thinking instead of going down the route of runtime bean generation. This would allow you to define models at runtime, without caring about the underlying implementation, and still give us pojos to work with and also provides more performance. further to this we really want to do our model implementation with ontology support. So that users can supply static and dynamic constraints to the properties they define on a class.

It's currently touch and go if either of these will make it into 5.0, I'm really hoping that we can do the later solution, but we currently have many more priorities :(


Mark
Godmar Back wrote: 
On Feb 20, 2008 12:30 PM, Edson Tirelli <tirelli@post.com> wrote:
  
   Godmar,

   Shadow Facts are a necessary evil in current version. Basically what they
do is keep the working memory consistent in face of attribute changes on the
facts, that may happen both internally and externally to the working memory.
    Our implementation to shadow facts is a lazy proxy that caches the
values until a safe point to synchronize the actual attribute value with the
one seen by the engine.

   So, the question is: given an object:

(Map) fact

   How can we create an identical copy of it (shadow), if there is no
"clone" operation?
    

Can you explain why you require the use of "clone()"?

Cloning a map is otherwise easy - it's also referred to as a "shallow
copy" -- HashMap's HashMap(Map) constructor will do it.
http://java.sun.com/j2se/1.4.2/docs/api/java/util/HashMap.html#HashMap(java.util.Map)
I know you know that, so explain what necessitates the use of clone().

  
More than that, the shadow must be a subclass of it.
    

java.util.HashMap is a subclass of Map.

  
   Most Collection and Map implementations have a single parameter
constructor that allows us to do:


proxy = (ShadowProxy) this.shadowClass.getConstructor( new Class[]{cls}
).newInstance( new Object[]{fact} );

    But the SingletonMap you were using does not accept that constructor.
So, one way is to explicit check if the fact is a SingletonMap and handle it
accordingly, but that is a specific class hack... is there any general
solution we can use?

    

Forget about the SingletonMap.  That was just one of the many things I
tried and failed.

Fundamentally, I would like Drools to process facts that were obtained
from real-world sources, and these facts have properties I do not know
in advance. Therefore, I cannot use beans (or using beans would be
highly inconvenient since it will require changes to Java code
whenever I'm referring to a new property, something I'd rather avoid.)

 - Godmar

  
    []s
    Edson

2008/2/20, Godmar Back <godmar@gmail.com>:
    
I don't really understand what you mean by "shadow".  What is the
purpose of such shadowing. Mark's email implies that it has to do with
concurrency protection; it's not clear what that means.

In my view, whatever purpose you pursue with "shadowing", it does not
justify treating beans and maps differently.

Your example of class Person shows that. If a person has two
attributes, name and age, then this is equivalent to a map with two
keys 'name' and 'age'.

Here's the mapping:

p.getName()    corresponds to m["name"]
p.getAge() corresponds to m["age"]

and setName/setAge accordingly.

Mathematically, a bean is an associative array with a fixed set of
keys (called "properties") that map to values. For all practical
purposes, that is the same as a map. There's no reason to treat them
differently. Wherever you'd do "getXXX()" with a bean you'd do
.get("XXX") with a map.

- Godmar

On Feb 20, 2008 11:25 AM, Edson Tirelli <tirelli@post.com> wrote:
      
   Ok, let me show one example. Imagine the class Person, with 2
        
attributes
    
(name and age) and the corresponding getter/setters.
   What are the data for that fact that must be shadowed? easy answer:
        
just
    
shadow all getXXX() methods (getName and getAge).

   Now, take a Map. What is the data that must be shadowed?

   So, we do our best to work with facts that don't follow the javabean
spec, but collections and maps are a complicated beast. Again, if you
        
have
    
suggestions on how to improve the current support we provide for them,
please share with us.

   []s
   Edson

2008/2/20, Godmar Back <godmar@gmail.com>:

        
On Feb 20, 2008 9:23 AM, Edson Tirelli <tirelli@post.com> wrote:
          
   Godmar,

   Short answer: collection/maps objects are not javabeans.

            
Explain why this is a problem.

What is it about JavaBeans that your algorithm relies upon?  Is it the
fact that the set of properties remains fixed and can be determined at
(fact) insertion time via reflection?

Otherwise, I do not see any conceptual difference between a map and a
          
bean.
        
If that is the difference, then please allow maps with an immutable
          
key
    
set.
        
- Godmar


          
   Long answer: collection/maps must be shadowed to ensure
            
consistency
    
during execution, but how can we shadow the data if it is not
            
exposed in
    
a
        
default, spec manner, as in javabeans? The algorithm we have in
            
place
    
right
        
now is bellow. As you can see, it is a weak algo, but was the best I
            
could
        
come up at that time. If you have any suggestions on how to improve
            
that, I
        
appreciate.

    public Object getShadow(final Object fact) throws
            
RuntimeDroolsException
        
{
        ShadowProxy proxy = null;
        if ( isShadowEnabled() ) {
            try {
                if ( Collection.class.isAssignableFrom(
            
this.shadowClass
    
)
        
|| Map.class.isAssignableFrom( this.shadowClass ) ) {
                     // if it is a collection, try to instantiate
            
using
    
constructor
                    try {
                        proxy = (ShadowProxy)
this.shadowClass.getConstructor( new Class[]{cls} ).newInstance( new
Object[]{fact} );
                     } catch ( Exception e ) {
                        // not possible to instantiate using
            
constructor
    
                    }
                }
                if ( proxy == null ) {
                    if ( this.instantiator == null ) {
                         this.setInstantiator();
                    }
                    proxy = (ShadowProxy)
            
this.instantiator.newInstance();
        
                }

                proxy.setShadowedObject( fact );
             } catch ( final Exception e ) {
                System.out.println( "shadow: " +proxy.getClass() +
            
":" +
    
fact.getClass() );
                throw new RuntimeDroolsException( "Error creating
            
shadow
    
fact for object: " + fact,
                                                   e );
            }
        }
        return proxy;


    }

     []s
     Edson

2008/2/19, Godmar Back <godmar@gmail.com>:
            
As a general comment, the examples for which I find Drools failing
              
are
    
not the actual examples for which my application is failing. It's
              
just
    
the smallest test case I was able to eliminate.

I'm now a bit concerned about your comment that Maps and
              
Collections
    
aren't well-defined as Facts. I am planning to make extensive use
              
of
    
them (that's also why I'd prefer to use the MVEL dialect, because
              
in
    
Java I cannot do this without creating Bean wrappers.)

Could you elaborate what makes the semantics not "well-defined".

I'm specifically concerned with immutable maps (such as the one
              
that
    
would have been returned by Collections.singletonMap), and with
collections of maps (such as those obtained via a "from"..."
              
clause).
    
I need to insert immutable maps as facts; I understand that the
              
items
    
returned by "from" aren't inserted as facts.

- Godmar

On Feb 19, 2008 3:11 PM, Edson Tirelli <tirelli@post.com> wrote:
              
   Drools tries to create the ShadowProxy. The reason is that it
                
does
        
not
            
know about the implementation... it just knows it is a Map and
                
as
    
so, it
        
must be shadowed. Problem is that SingletonMap is either  final
                
or
    
does
        
not
            
have a default constructor.
    My recommendation, besides opening a JIRA for this, is avoid
                
inserting
            
collections/maps directly as facts. The semantic for such facts
                
is
    
not
        
clearly defined and it may cause undesired behavior.

   []s
   Edson

2008/2/19, Godmar Back <godmar@gmail.com>:
                

Hi,

usings Drools 4.0.4 and MVEL 1.4, this simple rule:
---
package test;

import java.util.Collections;

dialect "mvel"

rule "Rule #1"
when
then
    insert(Collections.singletonMap("content", "hello"));
end
--

produces:
java.lang.IllegalAccessError: class

                  
org.drools.shadow.java.util.Collections$SingletonMapShadowProxy
    
cannot
        
access its superclass java.util.Collections$SingletonMap
        at java.lang.ClassLoader.defineClass1(Native Method)
        at
                  
java.lang.ClassLoader.defineClass(ClassLoader.java:620)
    
        at
                  
org.drools.rule.MapBackedClassLoader.fastFindClass(MapBackedClassLoader.java:60)
    
        at
                  
org.drools.rule.MapBackedClassLoader.loadClass(MapBackedClassLoader.java:79)
    
        at
                  
java.lang.ClassLoader.loadClass(ClassLoader.java:251)
    
        at
                  
org.drools.reteoo.Rete$ClassObjectTypeConf.loadOrGenerateProxy(Rete.java:547)
    
        at
                  
org.drools.reteoo.Rete$ClassObjectTypeConf.defineShadowProxyData(Rete.java:494)
    
        at
                  
org.drools.reteoo.Rete$ClassObjectTypeConf.<init>(Rete.java:461)
                
        at org.drools.reteoo.Rete.assertObject(Rete.java:152)
        at
                  
org.drools.reteoo.ReteooRuleBase.assertObject(ReteooRuleBase.java:192)
        
        at
                  
org.drools.reteoo.ReteooWorkingMemory.doInsert(ReteooWorkingMemory.java:71)
    
        at
                  
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:909)
    
        at
                  
org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:881)
    
        at
                  
org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:67)
    
        at
                  
org.drools.base.DefaultKnowledgeHelper.insert(DefaultKnowledgeHelper.java:61)
    
It's not clear to me why Drools creates Proxies for such
                  
classes
    
as
        
java.util.Collections, or does MVEL do it?

- Godmar
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--
  Edson Tirelli
  JBoss Drools Core Development
   Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
_______________________________________________
rules-users mailing list
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https://lists.jboss.org/mailman/listinfo/rules-users


                
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users

              

--
  Edson Tirelli
  JBoss Drools Core Development
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users


            
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users

          


--
  Edson Tirelli
  JBoss Drools Core Development
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users


        
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users

      

--
  Edson Tirelli
  JBoss Drools Core Development
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users


    
_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users