1. A method of providing XML data to a first data processing system, the method being performed by a second data processing system, the second data processing system being connected to the first data processing system via a network, the method comprising: receiving a first request over the network from the first data processing system, the first request comprising specifications for subsequent transfers of XML data from the second data processing system to the first data processing system, wherein the specifications specify for which type of XML documents which excerpts of XML data shall be sent to the first data processing system; and sending an acknowledge message to the first data processing system, the second data processing system indicating via the acknowledge message its ability to provide the excerpts of XML data of the types of XML documents in the subsequent data transfers.