Hi all, hi Dave,
back to this old discussion, in order to increase the BuiltIn behaviour by our
side, but while preserving the actual behaviour of the existing BuiltIn of Jena
and those developped by third parties, we would like to propose the following
patches. Our aim is to be able to send the removed context to some rules handle
by a RETE engine (while it's not possible for the time being).
First, we need an interface extending the current BuilIn one and provide a
method called when removed contexts have to be indicated.
public interface ReversibleBuiltIn extends BuiltIn {
/**
* This method is invoked when the builtin is called in a rule head with a
removed context.
* Such a use is only valid in a forward rule.
* @param args the array of argument values for the builtin, this is an
array
* of Nodes.
* @param length the length of the argument list, may be less than the
length of the args array
* for some rule engines
* @param context an removed context giving access to other relevant data
*/
public void reverseHeadAction(Node[] args, int length, RuleContext context);
}
Then, when need to define when to call the reverseHeadAction method, we propose
to complete RETEConflictSet::execute as following (changes are in bold red) :
public static void execute(RETERuleContext context, boolean isAdd) {
Rule rule = context.getRule();
BindingEnvironment env = context.getEnv();
ForwardRuleInfGraphI infGraph =
(ForwardRuleInfGraphI)context.getGraph();
if (infGraph.shouldTrace()) {
logger.info("Fired rule: " + rule.toShortString());
}
RETEEngine engine = context.getEngine();
engine.incRuleCount();
List<Triple> matchList = null;
if (infGraph.shouldLogDerivations() && isAdd) {
// Create derivation record
matchList = new ArrayList<>(rule.bodyLength());
for (int i = 0; i < rule.bodyLength(); i++) {
Object clause = rule.getBodyElement(i);
if (clause instanceof TriplePattern) {
matchList.add(env.instantiate((TriplePattern)clause));
}
}
}
for (int i = 0; i < rule.headLength(); i++) {
Object hClause = rule.getHeadElement(i);
if (hClause instanceof TriplePattern) {
Triple t = env.instantiate((TriplePattern) hClause);
// Used to filter out triples with literal subjects
// but this is not necessary
// if (!t.getSubject().isLiteral()) {
// Only add the result if it is legal at the RDF level.
// E.g. RDFS rules can create assertions about literals
// that we can't record in RDF
if (isAdd) {
if ( ! context.contains(t) ) {
engine.addTriple(t, true);
if (infGraph.shouldLogDerivations()) {
infGraph.logDerivation(t, new
RuleDerivation(rule, t, matchList, infGraph));
}
}
} else {
if ( context.contains(t)) {
// Remove the generated triple
engine.deleteTriple(t, true);
}
}
// }
} else if (hClause instanceof Functor && isAdd) {
Functor f = (Functor)hClause;
Builtin imp = f.getImplementor();
if (imp != null) {
imp.headAction(f.getBoundArgs(env), f.getArgLength(),
context);
} else {
throw new ReasonerException("Invoking undefined Functor " +
f.getName() +" in " + rule.toShortString());
}
else if (hClause instanceof Functor && !isAdd) {
Functor f = (Functor)hClause;
BuiltIn imp = f.getImplementor();
if (imp != null && imp instanceOf ReversibleBuiltIn ) {
((ReversibleBuiltIn)imp).reverseHeadAction(f.getBoundArgs(env),
f.getArgLength(), context);
}
} else if (hClause instanceof Rule) {
Rule r = (Rule)hClause;
if (r.isBackward()) {
if (isAdd) {
infGraph.addBRule(r.instantiate(env));
} else {
infGraph.deleteBRule(r.instantiate(env));
}
} else {
throw new ReasonerException("Found non-backward subrule : "
+ r);
}
}
}
}
Does it sounds good for you ? If yes, we will do these improvements, and a
ticket in Jira and send the patch for validation.
Best regards,
Chris.
Christophe FAGOT, PhD
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intactile DESIGN
Création d’interfaces + subtiles
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> Le 20 mars 2014 à 16:20, Dave Reynolds <[email protected]> a écrit :
>
>
> On 20/03/14 10:59, Christophe FAGOT wrote:
>>
>> Le 20 mars 2014 à 11:20, Dave Reynolds <[email protected]> a écrit :
>>
>>>
>>> On 20/03/14 09:46, Christophe FAGOT wrote:
>>>>
>>>> Le 19 mars 2014 à 18:46, Dave Reynolds <[email protected]> a écrit
>>>> :
>>>>
>>>>>
>>>>> On 19/03/14 16:46, Christophe FAGOT wrote:
>>>>>> Hi Jena folks,
>>>>>>
>>>>>> since I need to use Jena with its RETEEngine, I’m actually investigating
>>>>>> what is actually feasible / usable with this engine functionalities.
>>>>>>
>>>>>> I would like to develop my own BuiltIn, used in the head of a forward
>>>>>> rule, and doing some actions when a new rule context appears (due to
>>>>>> triples adding) for the body rule, while doing some other actions when a
>>>>>> rule context disappears (dur to triples removal) for this body rule.
>>>>>>
>>>>>> It appears in the RETEConflictSet (line 180) that a BuiltIn can receive
>>>>>> only … added RETERuleContext. Hence a BuiltIn action can only be called
>>>>>> when a RETERuleContext is added, never when a RETERuleContext is removed.
>>>>>>
>>>>>> Is their a reason for that ?
>>>>>
>>>>> The existing head builtins expect to only be fired when a potitive
>>>>> deduction is made. This is a legacy of the fact that the rule system was
>>>>> designed for monotonic inference and all the remove/non-monotonic
>>>>> processing is a hack.
>>>>
>>>> I don’t see the relationship between monotonic inference and remove
>>>> prohibited. A monotonic inference only means that when adding some facts
>>>> in the knowledge base, the previous inferred data can’t be removed, while
>>>> when removing some facts, new facts can’t be produced. And this is exactly
>>>> what Jena Rete engine perfectly does with « standard » triple patterns.
>>>> But when the head is a BuiltIn, that BuiltIn does not have a single chance
>>>> to act the same way. The BuildIn can only react to added triples. And the
>>>> only mandatory thing for a BuiltIn is to declare is it is monotonic or
>>>> not. But it’s behavior and the triples it adds/removes in the inference
>>>> graph are never verified to check if it really has a (non-)monotonic
>>>> behavior. But this is another story.
>>>
>>> The point is that builtins in the head are only useful if they have some
>>> side effect. Jena indeed handles removes when the rules are monotonic. As
>>> soon as you have side-effecting builtins then all bets are off. Even if a
>>> builtin's effect is reversible (which I take to be the case you are
>>> interested in) it's hard to guarantee all the necessary rules will fire in
>>> "remove" mode in the way you expect without the rule equivalent of
>>> reference counting.
>>
>> Absolutely agree. Would you be open to some little modifications in the RETE
>> classes source code, if that modifications improve the ability to extend the
>> RETE behavior (or to correct the problem of memory consumption), while
>> preserving the actual behavior of existing rules sets using BuiltIn (hence,
>> receiving only added data) ?
>
> Sure, patches welcome.
>
> I believe the right workflow would be to open a jira entry/ies for your
> enhancement and attach the changes as patch fines.
>
> Warning: I'm petty overloaded right now [*] so may need prompting to review
> any patches.
>
> Dave
>
> [*] For values of "right now" that seem to be depressingly permanent!
