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; receiving a second request from the first data processing system, wherein the first data processing system requests to receive excerpts of XML data with respect to a type of XML documents from the second data processing system; selecting the excerpts of XML data according to the specifications from documents having the type; wherein the type of XML documents relates to an XML document, wherein at least one of the first and second requests comprise a document identifier for the XML document, wherein the excerpts of XML data are comprised in the XML document, wherein the XML document identifier enables the second data processing system to identify the XML document; sending the excerpts of XML data over the network 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.