8:28 a.m.
I'd like to get some hints to improve the rules of my simple planning
system.
My simple planning system is derived from the HelloWorld Drools Project. The
job of my planning system is to calculate startTime and endTime as function
of duration and predecessors for each task. Each task has the fields
long duration;
Set<Task> predesessors;
long startTime;
long endTime;
For each task the rule (endTime = startTime + duration) should hold. If a
task has no predecessors, then its startTime should be 0. If a task has
predecessors, then is should start at the latest endTime of all
predecessors.
These are my DRL-rules:
rule "Calc EndTime"
no-loop true
when
$t : Task()
then
$t.setEndTime( $t.getStartTime() +
$t.getDuration() );
System.out.println( "Drools: Set " +
$t.getName() + ".EndTime to " + $t.getEndTime() );
update( $t );
end
rule "Calc StartTime without predecessors"
lock-on-active true
when
$t : Task(predecessorCount == 0)
then
$t.setStartTime( 0 );
System.out.println( "Drools: " +
$t.toString() + " can start immediately" );
update( $t );
end
rule "Calc StartTime with predecessors"
when
$t : Task(predecessorCount > 0, $predecessors :
predecessors )
# Checking EndTime > 0 for all predecessors means that
all EndTimes are
# initialy calculated. This is not what we realy want.
Actually we'd like
# to recalculate the successors EndTime, when ever it is
needed.
forall (
$succTask : Task( this == $t
)
$predTask : Task( this
memberOf $predecessors, endTime > 0 )
)
$endTime : Number()
from accumulate( $p : Task() from
$predecessors,
max($p.getEndTime()) )
then
$t.setStartTime( $endTime.longValue() );
System.out.println( "Drools: " +
$t.toString() + " has new StartTime" );
# !!!! If we did an update($t); here, we
would get an infinite recursion.
end
My TestClass creates three tasks: task0, task1 and task2. Each task has an
initial duration and (task0, task1) are predecessors of task2. It is
important that this example has no circular dependencies; otherwise the
rules, mentioned above, couldn't be applied.
After fireAllRuels() the endTime of task2 is calculated wrong, so obviously
the rule "Calc EndTime" should be activated. Is the rule-attribute (no-loop
= true) not the right solution to avoid circularity here?
Then the duration of task0 is updated outside of the rule engine. After a
second fireAllRuels() the endTime of task0 is recalculated, but task2 is not
recalculated at all. How can I tell the rule engine, that a task depends on
its predecessors?
I'd appreciate any input that could help me making this example work and if
it works very efficient on a big number of tasks it's brilliant. If anybody
is interested in my TestClass, to run this example with some logging, please
tell me.
Ralph Ammon
9:34 a.m.
On Thu, Jul 24, 2008 at 3:28 PM, Ralph Ammon <ralph.ammon(a)lisytec.de> wrote:
I'd like to get some hints to improve the rules of my simple
planning
system.
My simple planning system is derived from the HelloWorld Drools Project. The
job of my planning system is to calculate startTime and endTime as function
of duration and predecessors for each task. Each task has the fields
long duration;
Set<Task> predesessors;
long startTime;
long endTime;
For each task the rule (endTime = startTime + duration) should hold. If a
task has no predecessors, then its startTime should be 0. If a task has
predecessors, then is should start at the latest endTime of all
predecessors.
Maybe something like this would work?
rule "Calc EndTime"
no-loop true
when
$t : Task(endTime != (startTime+duration))
then
$t.setEndTime( $t.getStartTime() + $t.getDuration() );
System.out.println( "Drools: Set " + $t.getName() + ".EndTime to
"
+ $t.getEndTime() );
update( $t );
end
Afaik, this will also enable Drools to only check this rule if one of
the attributes used in the LHS is changed. So if you change any other
field of your object at some point, this rule will not be evaluated
again.
Please note that I haven't checked the syntax but I think that it
should work like this.
Best regards
Marcus
11:08 a.m.
New subject: AW: How to avoid circular rule activation for noncircular problems?
Thank you Marcus,
with your constraint I got rid of the "no-loop true" and the endTime is
recalculated when needed. So my first problem is really solved!
So I tried a similar constraint for the rule "Calc StartTime with
redecessors"
rule "Calc StartTime with predecessors"
when
$t : Task(predecessorCount > 0, $predecessors : predecessors
)
forall (
$succTask : Task( this == $t )
$predTask : Task( this memberOf
$predecessors, endTime > 0 )
)
$endTime : Number()
from accumulate( $p : Task() from $predecessors,
max($p.getEndTime()) )
# new constraint
Task(this == $t, eval($t.getStartTime() !=
$endTime.longValue()))
then
$t.setStartTime( $endTime.longValue() );
System.out.println( "Drools: " + $t.toString() + "
has new StartTime" );
# new update
update( $t );
end
The improvement is that I can do an update in the RHS without infinite
recursion. But the rule is still wrong, because it doesn't fire when the
maximum of predecessors endTimes changes.
Best regards
Ralph
3:17 a.m.
New subject: AW: How to avoid circular rule activation fornoncircular problems?
Sorry for the line breaks. Here I post my changes in a (hopefully) more readable format:
rule "Calc StartTime with predecessors"
when
$t : Task(predecessorCount > 0, $predecessors : predecessors )
forall( $succTask : Task( this == $t )
$predTask : Task( this memberOf $predecessors, endTime > 0 ) )
$endTime : Number() from accumulate ( $p : Task() from $predecessors,
max($p.getEndTime()) )
# new constraint
Task( this == $t, eval($t.getStartTime() != $endTime.longValue()) )
then
$t.setStartTime( $endTime.longValue() );
System.out.println( "Drools: " + $t.toString() + " has new
StartTime" );
# new update
update( $t );
end
Best regards
Ralph
8:09 a.m.
New subject: AW: How to avoid circular rule activationfornoncircular problems?
Thank you,
my problem is solved, the following rules work for all my test cases:
rule "Calc EndTime"
when
$t : Task( endTime != ( startTime + duration) )
then
$t.setEndTime( $t.getStartTime() + $t.getDuration() );
System.out.println( "Drools: Set " + $t.getName() + ".EndTime to
" + $t.getEndTime() );
update( $t );
end
rule "Calc StartTime without predecessors"
when
$t : Task( predecessorCount == 0, startTime > 0 )
then
$t.setStartTime( 0 );
System.out.println( "Drools: " + $t.toString() + " can start
immediately" );
update( $t );
end
rule "Calc StartTime with predecessors"
when
$t : Task( predecessorCount > 0, $oldStart : startTime, $predecessors :
predecessors )
$predTask : Task( this memberOf $predecessors, endTime > $oldStart )
then
$t.setStartTime( $predTask.getEndTime() );
System.out.println( "Drools: " + $t.toString() + " has new
StartTime" );
update( $t );
end
rule "Reset StartTime with predecessors"
when
$t : Task( predecessorCount > 0, $oldStart : startTime, $predecessors :
predecessors )
forall( $predTask : Task( this memberOf $predecessors )
Task( this == $predTask, endTime < $oldStart) )
then
$t.setStartTime( 0 );
System.out.println( "Drools: " + $t.toString() + " reset
StartTime" );
update( $t );
end
Best regards
Ralph
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4 comments
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participants (2)
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Marcus Ilgner -
Ralph Ammon