conways game of life
by Mark Proctor
For anyone looking for a good and complex example on how to write rules
properly, please look at Conways Game of Life in drools-examples, for
extra bonus points compare it to the old version in M1. You'll see
nearly all the logic is moved from java to the drl and we have removed
the need for nested objects by using objects relaitionally, which also
allows us to exploit cross products to drive the application.
Mark
2 months
java.lang.OutOfMemoryError: Java heap space
by vdelbart
Hello,
In my tests of the 4.0.3, I have some : java.lang.OutOfMemoryError.
So, I try a simple test with 10.000 sequential execution of 1 rule with no
context and just a workingmemorylogger and I have the error :
java.lang.OutOfMemoryError: Java heap space
My code is :
public class ExecReglesMemotyTest
{
private static final Reader DRL = new
InputStreamReader(ExecReglesMemotyTest.class
.getResourceAsStream("/rules/exemple.drl"));
private static final String FICHIER_LOG = "session";
/**
* @param args
*/
public static void main(String[] args)
{
try
{
PackageBuilder builder = new PackageBuilder();
builder.addPackageFromDrl(DRL);
RuleBase ruleBase = RuleBaseFactory.newRuleBase();
ruleBase.addPackage(builder.getPackage());
for (int i = 0; i < 10000; i++)
{
StatefulSession session = ruleBase.newStatefulSession();
WorkingMemoryFileLogger logger = new WorkingMemoryFileLogger(session);
logger.setFileName(FICHIER_LOG);
session.fireAllRules();
logger.writeToDisk();
session.dispose();
}
}
catch (Exception e)
{
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
with this rule (doesn't matter):
#created on: Fri Nov 09 15:48:45 CET 2007
package initPackage
#list any import classes here.
rule "ERG9"
when
then
end
I try this in 4.0.1, and it's working (no OutOfMemoryError)
What's the problem ?
thanks for any information,
V.
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13 years, 1 month
Log4j in the rules?
by granz＠MIT.EDU
Hi,
Is it possible to use Log4j inside the rules (RHS)?? (drl file)
Thanks,
Fabrice
14 years, 2 months
About for and inheritance
by Chris Woodrow
Hi,
I recently find out a few issues using for, and I wanted to share it with
you. I made a simple exemple to illustrate my purpose.
My classes are (I did not represent accessors & constructors):
public class Cheese {
protected String name;
}
public class FrenchCheese extends Cheese{
private String smell;
}
public class Person {
private Cheese likes;
}
Here is my rule set :
package rules
rule "likes cheese"
when
$person : Person ()
Cheese( ) from $person.getLikes()
then
System.out.println("likes cheese");
end
rule "likes french cheese"
when
$person : Person ()
FrenchCheese( ) from $person.getLikes()
then
System.out.println("likes french cheese");
end
First test :
Cheese cheese = new FrenchCheese("good", "camembert");
Person person = new Person();
person.setLikes(cheese);
Output :
likes french cheese
likes cheese
Wich is expected...
Second test :
Cheese cheese = new Cheese();
Person person = new Person();
person.setLikes(cheese);
Output :
likes french cheese
likes cheese
That's the first strange thing. As far as I am concerned, rule "likes french
cheese" should not match (since a Cheese is not a FrenchCheese).
I made a change to the second rule :
rule "likes french cheese"
when
$person : Person ()
FrenchCheese( smell == "good" ) from $person.getLikes()
then
System.out.println("likes french cheese");
end
Third test :
Cheese cheese = new Cheese();
Person person = new Person();
person.setLikes(cheese);
output :
It throwed an exception : Exception in thread "main"
java.lang.ClassCastException: rules.Cheese
I am not saying the ClassCastException is not to expect in such a case but I
think I would simply expect it not to match (as far as a Cheese is not a
FrenchCheese).
Chris
14 years, 10 months
Drools 4.0, Support for multiple pattern in accumulate source pattern
by Juergen
It appears as if accumulate does support only a single pattern CE as
source pattern, e.g.:
Number() from accumulate(
Cheese(
price : price
),
sum( price )
)
Is it possible to have more than one pattern in the source pattern, e.g.:
Number() from accumulate(
Cheese(
price : price,
type : type
)
Person(
favouriteCheese == type,
age > 30
),
sum( price )
)
The same could be said for collect, but there the problem to specify
which item of a matching tuple is to be collected, but this could be
handled recreating collect via accumulate, e.g.:
Collection() from accumulate(
cheese : Cheese(
type : type
)
Person(
favouriteCheese == type,
age > 30
),
collect( cheese )
)
14 years, 11 months
Why is a flat object recommended?
by Christie, Blair
In the documents this is dicussed briefly:
"). Object models can often have complex relationships and hierarchies
in them - for rules you will want to simplify and flatten the model
where possible, and let the rule engine infer relationships (as it
provides future flexibility."
What does it mean that the rule engine can infer relationships?
Are there performance reasons for having a flat model?
Cheers,
Blair
16 years, 3 months
Stateless session and rule flows
by Yoni Mazar
Hi Guys,
We are trying to work with drools with stateless session (Sequential) and to
apply rule flows.
we use the following code:
//define diagnosis and patient here
...
StatelessSession session = ruleBase.newStatelessSession();
//Here we would like to use: session.startProcess("ruleflow id") but this is
a method which belongs to
//StatefullSession only.
session.execute(new Object[] {diagnosis, patient});
How can we do that in steteless mode?
Thanks,
Yoni
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16 years, 7 months
