1. A method for generating at least one output expression from at least one input expression, the method comprising the step of applying at least one transformation to at least one sub-expression of the at least one input expression to produce the at least one output expression, wherein the at least one input expression is a logical expression of a first policy and the at least one output expression is at least one logical expression of a second policy, wherein said transformation compares a sub-expression in a representation of said first policy with a sub-expression in a representation of a rule, wherein said at least one output expression is another sub-expression of said rule if said compared sub-expressions are substantially equivalent, wherein the step of applying at least one transformation to at least one sub-expression of the at least one input expression to produce the at least one output expression comprises the step of replacing at least one input sub-expression with at least one output sub-expression, wherein the at least one input sub-expression is at least one element of at least one set of input sub-expressions, and the at least one output sub-expression is at least one element of at least one set of output sub-expressions, wherein the step of replacing the at least one input sub-expression with the at least one output sub-expression comprises comparing the at least one sub-expression of the input expression to each element of the at least one set of input sub-expressions, finding a match between the at least one sub-expression of the input expression and at least one element of the at least one set of input sub-expressions, and substituting the at least one sub-expression of the input expression that matches the at least one element of the at least one set of input sub-expressions with at least one output sub-expression of the at least one set of output sub-expressions that corresponds to the at least one element of the at least one set of input sub-expressions, and wherein one or more steps of said method are performed by one or more hardware devices.