You can use the ASCENDING or DESCENDING keyword with any tag, without having to designate one or the other when you build the tag. The DESCENDING() function will tell you which way the current order is going. So, a method to do this would be as follows:

lcCurOrder = ORDER()
llDescend  = DESCENDING()
IF llDescend
   SET ORDER TO (lcCurOrder) ASCENDING
ELSE
   SET ORDER TO (lcCurOrder) DESCENDING
ENDIF

>I have a list of data that the client wants to be able to click on a control and have the data displayed in ascending order, click the control again and it is in descending order. Using the data environment, without creating an index each way, is there a way?