23. A system including: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations 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.
23. A system including: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations 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. 46. The system of claim 23 further including instructions that when executed by one or more computers cause the one or more computers to perform operations that include, in each results row, indicating whether the output that will be generated is changed from an output that was indicated for a previous version of the rule specification.