1. A method for a client to interface with a server, the method comprising: at the client, making a plurality of application programming interface (API) calls to the server; wherein each API call in the plurality of API calls requests the server to perform an action; wherein making the plurality of API calls comprises: for a first API call that requests a connection to the server: creating a first client web service message to request the connection; for a second API call that requests execution, by the server, of an expression that conforms to the XQuery language: creating a second client web service message that encapsulates the expression that conforms to the XQuery language, wherein the expression specifies an XQuery operation to be performed on XML data; and sending, via web service communications, the client web service messages to the server; receiving, at the client, from the server, via web service communications, a server web service message; wherein the server web service message contains a sequence of items: wherein the sequence of items contains at least part of results from execution of the XQuery expression; wherein execution of the XQuery expression comprises performance of the XQuery operation on the XML data; wherein the method is performed by one or more computing devices.