What are the myths about rules engine? [closed]

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I'm writing a presentation about rule engine technology, specifically JBoss Drools.

What are some of the 'myths' about rule engines.

One I can think of is that it allows business users to control the rule engine, I believe it is possible, but it requires control and education - and not all business users are able to do it.

Do you agree/disagree? Does anybody else have any thoughts?

Happy to release my final 'findings' under Creative Commons...

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I don't know about myths, but I agree that having business people maintain rules is not a slam dunk.

I think expecting business folks to have the patience and anal retentive attention to detail required to do IT's job is a fantasy. It's been in play ever since 3G languages (graphical approaches to programming) have been offered as a way to get secretaries to write code so the programmers could all be fired.

I'd point out that as the size of the rule set increases, the possibility of ensuring that it's correct and self-consistent goes down. If your rules set has thousands of rules it'll be hard to test.

Speaking of which, combinatorial explosion of combinations will make it hard to test a rules engine.

Rules engines are terrific technology, but be careful.

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Actually, having used drools heavily, I disagree with you on your point about users having the ability to do stuff easily, I think it's relatively trivial to provide users with a simple interface to generate powerful rules dynamically.

One I would definitely add to the list is:

Myth: Rules engines are slow!

Not so, again, I've pushed even thousands of events per second through drools quite easily.

Another which I absolutely loathed was:

Myth: It's too heavy weight and complex to use.

Nonsense, the syntax is trivial and with a few lines of java, you can do some really funky stuff! Sorry if this appears to be a rant, had months of this crap at a previous employer as I wad trying to introduce this tech!

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Myths...
1/ Business users can:
author rules
deploy them
test them
run them
Whithout the help of IT... I have delivered a training for a client who was actually thinking that it was true because the salesman said so... ah ah ah they made my day/mounth/year !!!

Can you seriously think about a company who will take the risk to deploy a service in the back of the IT team?? no way!
You need security as well to prevent me writing a rule stating:
if the name of the client is "Damien" then 100% discount - groovy baby!

The architecture of a project cannot be done by non-technical users

2/ You can manage rule project easily without having to worry about anything.
There is limit of number of rules you can deal with. In theory one could have as many rules as they want but this is not entirely correct. JRules stop synchronizing rules between Eclipse and RTS from around 3,000 rules. It will take forever if you have a project with 100,000 rules all in RETE. Building the tree will take a long time. Even in Sequential mode it takes a long time to proceed.
You cannot use a rule repository like the folder "My Documents" and just keep on adding rules.

3/ Business users can write all kind of rules without any training.
Different things:
a/ order of conditions may impact performance.
b/ some rules are complex and need a good understanding of the language
c/ the algorithm used can impact the result of the execution
d/ a single badly written rule can multiply the execution time by n.
I worked on a project where only 1 rule was responsible for some random timeouts.
e/ Some complex problem can be express in one rule.
This problem is solve in one rule and has one result:
There are four Golfers standing at a tea, in a line from left to right.
- The golfer to the Fred’s immediate right is wearing blue pants
- Joe is second in line
- Bob is wearing plaid pants
- Tom isn’t in position one or four, and he isn’t wearing the orange pants
BTW: This is an JBoss example.
How can a business user do this?

4/ Rule engine can do backward chaining
I think JBoss say they can but I am not sure about this. Blaze and JRules cannot.

5/ One doesn't need any programme language to write rules.
Correct, but you will need some to execute the rules. Except if you are using a simple XSD as Object Model. But your Decision Service will not do that much clever thing.

6/ It is slower than JAVA
Of course but by using BRMS you are externalizing the business logic so it has a cost.
Exactly like when you externalize data. The database call has a cost.
I have sent 5,000 objects into the working memory of JRules with a project containing 4 dummy rules which were calling each other... Performance test purpose
Result: 19 Millions rules executed in 75 seconds. Do your maths... it is not that slow.

7/ You can do anything in a rule
Do not make database call in a rule (especially in the conditions). Using Rete, in theory, a rule could "test" the condition to find matching result in the memory thousands of time.
No one want to call a database that much in an application.

Hope it helps