Hi Richard,

Glad I can be of help (this forum as a whole is actually very helpful).

Reading your email you understand me correctly (you even picked up on the implicit AND between pattern matches).

With a bit of imagination complex problems can be solved with Drools; just like programming you need to adjust your mindset sometimes and try a different tact.

Personally, if your rules are not user-facing, I wouldn't worry about DSL - even if they do don't worry for the time being!

Make sure to read the excellent manual, many people have put a lot of work into this and it is invaluable.

Read about "dialect" to answer your question about rule language, to save me copy and pasting.

Good luck,

Mike

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Richard Bremner
Sent: 02 May 2008 11:38
To: Rules Users List
Subject: Re: [rules-users] newbie question on "when" condition syntax

Hi Mike,

Thanks very much, after a few minutes of staring I think I have understood your very well put answer!

If I understand you right, what is happening is:

Test( $y : y )

This means, WHEN there is an instance of Test, assign the value of its "y" property to $y

AND

WHEN there is an instance of Test where it's "x" property is equal to $y + 1

THEN fire.

I think I understand that. I am going to need to do this with some pretty complicated formulae, containing up to 8 different variables. I have a fixed data set and need to find certain patterns in them based on the formulae. I have most of the program figured out, my only trouble is expressing my formulae in the correct syntax. I will try to extend this principle you have explained to me and hope it can cope with the extra complication... unless there would be a better way to achieve this?

I am really sorry but I am totally new to drools - but am committed to using it on a project so I guess I'm going to get to know it pretty well :-)

I read briefly that one can define a DSL, I might look at this eventually to build an easier mechanism for expressing my formulae - if that can be achieved using a DSL.

Can the whole rule be defined in Groovy/Java - if so I might be easier doing that. I have so much work to do!

many thanks

Richard

2008/5/2 Anstis, Michael (M.) <manstis1@ford.com>:

Hi Richard,

The "when" section matches fact (object) patterns, so your requirement could be written as:-

when there is a Test Fact 'A' and another Test Fact 'B' where "the 'x' property of 'A'" equals "the 'y' property of fact 'B' plus 1" then.....

This would become:-

rule "Rule 1"

when

    Test( $y : y )

    Test( x == ($y + 1) )

then

    System.out.println("Rule 1 matches");

end



By default both patterns can match the same object, so test data:-

A : x = 1, y = 1

B : x = 2, y = 1

Will cause the rule to activate twice:-

A and B

B and B

With kind regards,

Mike

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Richard Bremner
Sent: 02 May 2008 08:53
To: rules-users@lists.jboss.org
Subject: [rules-users] newbie question on "when" condition syntax

Hi,

say I have a class with two fields, x and y:

public class Test {
int x = 1;
int y = 2;

getters/setters...
}

I would like a rule which fires when y = x + 1

my initial thought would be something like:

rule "Rule 1"

when
test : Test (y == x + 1)
then
System.out.println("Rule 1 matches.");

end

but this is invalid syntax and I can not find any examples of such a rule. I'm doing my best but reading the manual etc. I'm struggling with the syntax here and can't figure it out.

any help really appreciated!

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