21. A system according to claim 20, further comprising: a reference to a software object for a rule to be created; an object method for examining the source which has been input by the user; and an object method for assigning a null value to the second structured information format attribute value using the software object for the rule to be created, when the source which has been input by the user indicates no source is to be used.
20. A system according to claim 15, wherein the user interface object further comprises: a reference to a software object for an interactive user input of a source for inputting the second structured information format attribute value; a reference to a software object for an interactive user input of the second structured information format attribute value; an object method for obtaining interactive input from the user of the source for inputting the second structured information format attribute value using the software object for the interactive user input of the source for inputting the second structured information format attribute value; and an object method for obtaining interactive input from the user of the second structured information format attribute value using the software object for the interactive user input of the second structured information format attribute value.