On Jun 24, 2008, at 2:51 PM, Deepak Pol wrote:
Now following are some questions I have:
1. Since the rules defined are being applied to any data, I want the
rules to be created once and shared by different sessions for
different data. For eg there can be a rule which says if total > 100
then return list of users u1, u2 and u3. Now for different
organizations total can be different and each organization can run
rules engine with its own data but the rules themselves are same so
I want to share them across different organizations. Each
organization will have its own session and data and the same rules
in the memory are executed with this data.
What I found in Jess docs was, you need to initialize the rule
engine by using new Rete(); and add the rule language file (*.clp)
and the data to the working memory. But like in above example, if I
want to add the data for some other organization but for the same
rules then I need to create another instance of Rete and provide the
rule language file to it in which case I end up having one file in
working memory for each organization. Is there any way to avoid this
and share the file for different data or for different sessions?
Yes, in several different ways. First of all, you don't need to hard
code values like "100" in the rules; you can supply these as data. For
example, a rule might say
if total > threshold then return list of users
and then each client could supply their own value of "threshold". That
way the rules are the same for everybody.
Secondly, you can have multiple values of "threshold" in the same
engine at the same time. You could have
if processing client #1 and total for client #1 > threshold for client
#1 then...
Finally, multiple instances of the rule engine can share a single
loaded set of rules; this is called "peering" and it's new in Jess
7.1, which is about to go final.
2. As per my understanding, the only way to control the flow of
rules execution is by creating different modules.
No, that's just one way.
If I have a condition like if Module_1 fires (i.e at least one rule
from module is fired) the focus module_2 else focus module_3. This
conditions can get even more complex. And also note that all rules
from module_1 should get fired so I can't have focus statement in
action part of any rule of module_1 since it will immediately focus
to new module and other rules from module_1 would be skipped.
Currenly I am planning to do it by having a global variable for each
such condition. For eg if any rule from module_1 is fired then make
this variable true and use it for further control. But as the
conditions become more and more complex and provided that I want to
create the language through some apis against using an existing one;
I am not sure how much feasible this would be. Any suggestions on
this?
There's a concept of a "focus stack". The focus stack keeps track of
the order in which modules will be activated. You can add and remove
modules from the stack at any time. So you an easily express "when
all the rules in this module have fired, proceed to module 2".
3. I want to have some modules (which would be set of rules) which
are exclusive i.e. only one of them should fire even if others also
match. I can do this with auto-focus for the first rule in each
module but how to avoid others from firing. I tried halt but didn't
work. Retracting the facts as soon as they fire is not a feasible
option since the same fact might be used in some other rule in the
same module which I still want to fire.
There are other ways to do this besides retracting facts; for
instance, you can do it by asserting a fact signaling that one of the
rules has fired, then make all the rules in the set match the absence
of that fact.
Any help in above ragards would be really appreciable.
Thanks in advance,
- Deepak
---------------------------------------------------------
Ernest Friedman-Hill
Informatics & Decision Sciences, Sandia National Laboratories
PO Box 969, MS 9012, Livermore, CA 94550
http://www.jessrules.com
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