[rules-users] Drools basic questions.

[Anstis, Michael (M.)]

Hi,

1. The dollar sign has no significance. What appears to the left of the
colon is simply an identifier binding the object\field to a variable.
Some people prefix their identifiers with dollar signs so that
identifiers are easier to see in code.

	$stilton : Cheese( type == "stilton" )
      Cheesery( cheeses contains $stilton )

	stilton : Cheese( type == "stilton" )
      Cheesery( cheeses contains stilton )

	some_identifier : Cheese( type == "stilton" )
      Cheesery( cheeses contains some_identifier )

2. 
    - cheapStilton : Cheese( type == "stilton", price < 10 )
	Binds a variable "cheapStilton" to a Fact (Object) of type
Cheese where it's field "type" equals "stilton" 
	and it's field "price" is less than 10. Both "type" and "price"
are compared to literals.

    - cheapStilton : Cheese( type == "stilton", price < newPrice)
	Binds a variable "cheapStilton" to a Fact (Object) of type
Cheese where it's field "type" equals "stilton"
	and it's field "price" is less than another identifier
"newPrice". "Type" is compared to a literal and "price" is
	compared to a variable. The variable would need to have been
bound somewhere else in the rule; for example:-

	Price( newPrice : price )
    	cheapStilton : Cheese( type == "stilton", price < newPrice)

With kind regards,

Mike

-----Original Message-----
From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Mithun
Sent: 17 May 2007 06:04
To: rules-users at lists.jboss.org
Subject: [rules-users] Drools basic questions.


I am new to drools, so i have some basic doubts. 

1. what does the dollar sign represent in the following rule? what is
the
difference when u prefix and dont prefix a variable with the dollar
sign?
    - $stilton : Cheese( type == "stilton" )
      Cheesery( cheeses contains $stilton )

2. what is the difference between the following rule statements ?
    - cheapStilton : Cheese( type == "stilton", price < 10 ) and
    - cheapStilton : Cheese( type == "stilton", price < newPrice)

   how does the rule base get access to the variable newPrice, in the
above
rule statement? Please help.

Thank you.
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