According to a first aspect of the present invention there is provided a method of operating an XML Document Management Server in an IP Multimedia Subsystem. The method comprises receiving a message from a user terminal requesting an XML document, the XML document conforming to a given structure and containing one or more service rules relating to a service, retrieving an XML document containing said service rules from a data storage entity. If the structure of the retrieved XML document differs from said given structure, adapting a rule or rules of the retrieved XML document such that the XML document conforms to said given structure, and sending the adapted XML document to the user terminal.