Hi, Is there a way to use <validator> or perhaps <filter> options to avoid the selection of the same dataset twice in different parameters of a tool. E.g. a tool has 2 "data" type parameters of the same type, but it should not be possible for the user to set both parameters to the same dataset. So if his history contains files A,B, and C and he selects A in his first parameter, then the second parameter should display only the options B and C. Thanks and regards, Pieter Lukasse Wageningen UR, Plant Research International Departments of Bioscience and Bioinformatics Wageningen Campus, Building 107, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands +31-317480891; skype: pieter.lukasse.wur http://www.pri.wur.nl<http://www.pri.wur.nl/>