1. A computer-implemented method comprising: receiving an extended markup language (XML) query that requests data from one or more XML documents; evaluating the XML query to determine one or more XML results of the XML query, wherein for a particular XML result, of the one or more XML results, evaluating the XML query comprises: instantiating, in volatile memory, a particular data structure that represents the particular XML result, wherein the particular data structure is encoded in accordance with one or more tags that are specified in the XML query, but the particular data structure does not store the one or more tags; and storing, in the particular data structure, one or more locators that respectively point to one or more fragments in the one or more XML documents, wherein the particular data structure stores the one or more locators but does not store the one or more fragments pointed to by the one or more locators; in response to a request indicating the particular XML result, generating a serialized representation of the particular XML result based at least on the particular data structure; wherein the method is performed by one or more computing devices.