Modern computational science applications are becoming increasingly multi-disciplinaty involving widely distributed research teams and their underlying computational platforms. A common problem for the grid applications used in these environments is the necessity to couple multiple,.pamllel subsystems, with examples ranging from data exchanges between cooperating, linked parallel pmgmms, to concurrent data streaming to distributed storage engines. This paper presents the X Change,,, middlrware infrastructurefor coupling componentized distributed applications. XChange,,, implements the basic functionality of well-known services like the CCA Forum's MxN pmject, by providing efficientdata redistribution acmss parallel application components. Beyond such basicfinctionaliv,however:XChange,,, also addresses M O of the problemsfaced by wide area scientific collaborations, which are ( I ) the need to deal with dynamic applicatiodcomponent behaviors, such as dynamic arrivals and departure...