Business applications often exchange large amounts of enterprise data stored in legacy systems. The advent of XML as a standard specification format has improved applications interoperability. However, optimizing the performance of XML data exchange, in particular, when data volumes are large, is still in its infancy. Quite often, the target system has to undo some of the work the source did to assemble documents in order to map XML elements into its own data structures. This publish&map process is both resource and time consuming. In this paper, we develop a middle-tier Web services architecture to optimize the exchange of large XML data volumes. The key idea is to allow systems to negotiate the data exchange process using an extension to WSDL. The source (target) can specify document fragments that it is willing to produce (consume). Given these fragmentations, the middle-ware instruments the data exchange process between the two systems to minimize the number of necessary operations and optimize the distributed processing between the source and the target systems. We show that our new exchange paradigm outperforms publish&map and enables more flexible scenarios without necessitating substantial modifications to the underlying systems.