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13.21. Basic Conditional Elements

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Table 13.4. Basic Conditional Elements
Name Description Example Additional options
and
The Conditional Element and is used to group other Conditional Elements into a logical conjunction. JBoss Rules supports both prefix and and infix and. It supports explicit grouping with parentheses. You can also use traditional infix and prefix and. 
//infixAnd
Cheese( cheeseType : type ) and Person( favouriteCheese == cheeseType )
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//infixAnd with grouping
( Cheese( cheeseType : type ) and
  ( Person( favouriteCheese == cheeseType ) or 
    Person( favouriteCheese == cheeseType ) )
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Prefix and is also supported: 
(and Cheese( cheeseType : type )
     Person( favouriteCheese == cheeseType ) )
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The root element of the LHS is an implicit prefix and and doesn't need to be specified: 
when
    Cheese( cheeseType : type )
    Person( favouriteCheese == cheeseType )
then
    ...
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or
This is a shortcut for generating two or more similar rules. JBoss Rules supports both prefix or and infix or. You can use traditional infix, prefix and explicit grouping parentheses. 
//infixOr
Cheese( cheeseType : type ) or Person( favouriteCheese == cheeseType )
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//infixOr with grouping
( Cheese( cheeseType : type ) or
  ( Person( favouriteCheese == cheeseType ) and
    Person( favouriteCheese == cheeseType ) )
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(or Person( sex == "f", age > 60 )
    Person( sex == "m", age > 65 )
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Allows for optional pattern binding. Each pattern must be bound separately, using eponymous variables: 
pensioner : ( Person( sex == "f", age > 60 ) or Person( sex == "m", age > 65 ) )
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(or pensioner : Person( sex == "f", age > 60 ) 
    pensioner : Person( sex == "m", age > 65 ) )
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not
This checks to ensure an object specified as absent is not included in the Working Memory. It may be followed by parentheses around the condition elements it applies to. (In a single pattern you can omit the parentheses.) 
// Brackets are optional:
not Bus(color == "red")
// Brackets are optional:
not ( Bus(color == "red", number == 42) )
// "not" with nested infix and - two patterns,
// brackets are requires:
not ( Bus(color == "red") and
      Bus(color == "blue") )
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exists
This checks the working memory to see if a specified item exists. The keyword exists must be followed by parentheses around the CEs that it applies to. (In a single pattern you can omit the parentheses.) 
exists Bus(color == "red")
// brackets are optional:
exists ( Bus(color == "red", number == 42) )
// "exists" with nested infix and,
// brackets are required:
exists ( Bus(color == "red") and
         Bus(color == "blue") )
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Note

The behavior of the Conditional Element or is different from the connective || for constraints and restrictions in field constraints. The engine cannot interpret the Conditional Element or. Instead, a rule with or is rewritten as a number of subrules. This process ultimately results in a rule that has a single or as the root node and one subrule for each of its CEs. Each subrule can activate and fire like any normal rule; there is no special behavior or interaction between these subrules.
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