Such behavior sounds like it might be useful, but isn't this due to a lack
of support in drools for expressing the re-assertion of a fact? drools current
behavior seems correct to me. There just isn't any mechanism for expressing
the "backing" of an existing fact.
In your example, I would expect drools to do just what it does. Only the
second rule is asserting a fact. The second rule is just testing for a fact's
existence, not re-asserting the fact. Maybe a more illustrative example
would be:
rule "assert fact"
when
Integer()
then
assertLogical(new Fact());
end
rule "reassert fact"
when
Float()
f : Fact()
then
assertLogical(f);
end
Thus, the fact wouldn't be auto-retracted until both the int and the float
were retracted. This looks like it could very difficult to debug though.
Hello Juergen,
A logically asserted object seems to be retracted only when the
fact(s) leading to its inital assertion are invalid/retracted. Even if
the depended object is "backed" by some other rule/facts.
so in the following example:
1 => A
2 => A
As soon, as 1 is asserted, A is asserted. When 2 is asserted, the
truth of A is "backed" but nothing happens as A is already asserted
(in terms of memory management, the reference counter would increase i
guess).
When 1 becomes false and is retracted, the truth of A is still given
by 2 => A and A should not be retracted (which it is). Only if 2 also
becomes false and is retracted, A should be retracted too.
Gets even more interesting if a fact is backed by itself after inital
assertion: A => A
Without this behaviour logical assertion are not useful in my opinion.
Checked it with JESS which does it properly.
Will it change in the future, and probably already for 3.0?
Juergen.
Example:
--------
DRL:
----
rule "1"
when
s : String()
then
System.out.println("s=" + s);
end
rule "2"
when
i : Integer()
then
System.out.println("i=" + i);
assertLogical("A");
end
Java:
-----
FactHandle h = workingMemory.assertObject(new Integer(1));
workingMemory.fireAllRules();
workingMemory.assertObject(new Integer(2));
workingMemory.fireAllRules();
workingMemory.retractObject(h); // A will be retracted, but should not
workingMemory.fireAllRules();
List l = workingMemory.getObjects();
System.out.println(l);
