Interesting analogy, but careful here:

"Statefull is just series of stateless session where you transfer state from one session to another."

    Not sure what lead you to think that way, but it is actually the opposite, and trying to explain that will make things REALLY confusing for some. So, I would recommend anyone not interested in knowing internal details to **stop reading here**!

    Ok, if you are still reading, then I will try to explain in the simplest way I can: "there is no such thing as stateless session in Drools internals". Deep in drools internals, there is only stateful working memory, that is exposed to the user in 2 different ways: a properly stateful session, that allows users to manage the state, and a helper object that we call "staless session". This helper staless session object, among other things, simply holds a reference to the kbase and when the execute(...) method is called, internally it creates a stateful session, inserts the facts, fire the rules and disposes the session automatically. There are a bunch of other helper mechanisms there, but the essence is just that: simplify the use of stateful sessions for stateless scenarios.

    Edson

2010/3/8 Pavel Tavoda <pavel.tavoda@gmail.com>
It's like synchronous vs. asynchronous communication. In reality it's
always asynchronous but from top view it appear synchronous.
Similar to stateless vs. statefull. Statefull is just series of
stateless session where you transfer state from one session to
another. Look for Drools statefull persistency. In reality it is
series of stateless sessions where you store status from one session
result and use it as start for another session plus some new changes.
This is my point of view of difference between stateless/statefull
session specially how Drools make it.

Regards

Pavel

On Mon, Mar 8, 2010 at 4:23 PM, Tim de Jager <tim.dejager@student.hu.nl> wrote:
>
> Hi everybody,
>
> I'm currently doing my bachelor thesis on Rule engines. This includes
> comapring different Rule engine products. I have set up a small Java program
> (Conway's game of life) and I'm writing the 'engine' in different Rule
> engines, while keeping the same GUI,CellGrid etc. I have already made a
> Drools based engine.
>
> I have been studying the Rule engine subject for somewhat more then a month
> now. And I'm currently seeing two different developments namely the use of
> an inference engine and the generation of embedded code instead (Take,
> Visual Rules etc.)  I can see some of the pro's and cons with both
> paradigms. But I'm wondering what opinion some of you guys have on the
> subject.
>
> I can see that without inferencing  it is very hard (or even impossible) to
> keep a statefull session inside the rule engine, haven't seen a
> non-inferencing rule engine which does offer this possibility. And also lose
> features like TMS. But what would be a concrete example where a statefull
> session is absolutely necessary? Instead of letting the engine reason over
> all the facts in stateless way. And managing conflicts with a ruleflow (see
> Visual Rules for a nice example).
>
> I'm looking forward to hearing your thoughts.
>
> Thanks,
>
> Tim
>
> P.S I already read two of Mark Proctors blogs on inferencing, but while
> enlightening, they didn't supply me with a definitive awnser
> --
> View this message in context: http://n3.nabble.com/Inferencing-tp435411p435411.html
> Sent from the Drools - User mailing list archive at Nabble.com.
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--
 Edson Tirelli
 JBoss Drools Core Development
 JBoss by Red Hat @ www.jboss.com