1. A method for specifying the behavior of a functional component in a computation system, including: providing a user interface for creating a table having at least one input column and at least one output column, wherein each input column is associated with an input variable and each output column is associated with an output variable; in at least one row of the table, receiving one or more conditions on input values in respective input columns, the conditions in the at least one row identifying more than one set of potential values of the input variables, and receiving one or more output values in respective output columns, thereby defining a rule case of a rule specification; generating a function for transforming data based on the rule specification; associating the function with the functional component; receiving changes to values in the rule specification, the changes including new potential values of the input variables for a condition; confirming that the changed rule specification is valid; and associating a new function with the functional component.