Hi all, http://technology.amis.nl/blog/704/bill-of-materials-and-hierarchical-queries-which-component-contains-a-component-that I found the structure of the Bill of Material model I am developing as above mentioned. But I really don't know how the UML should be drawn and the hibernate mapping should be written. It seems to be composite pattern but there are actually two class. Can anyone give me some hints? Thanks a lot. Kit