1. A computer implemented method for processing queries, the method on information processing system comprising: executing on an information processing system the following: receiving a data query for a set of hierarchical markup documents; extracting at least one query path expression from the data query; processing the query path expression against at least one shared hierarchical markup document in a plurality of shared hierarchical markup documents, wherein the plurality of shared hierarchical documents is separate and distinct from the set of hierarchical markup documents, and wherein each of the plurality of shared hierarchical markup documents is a hierarchical markup document derived from at least two hierarchical markup documents in the set of hierarchical markup documents and consists only of a single rooted tree that is common to the at least two hierarchical markup documents, wherein each hierarchical markup document in the set of hierarchical markup documents is a separate and distinct original hierarchical markup document, thereby being original with respect to and different from all other hierarchical markup documents in the set of hierarchical markup documents; determining if the at least one shared hierarchical markup document completely matches the query path expression; generating, based on the at least one shared hierarchical markup document completely matching the query path expression, a query result for the data query based on the processing of the query path expression against at least one of the shared hierarchical markup document; based on the at least one shared hierarchical markup document partially matching the query path expression, processing a remaining portion of the query path expression failing to be matched by the at least one shared hierarchical markup document to at least one difference hierarchical markup document, wherein the at least one difference hierarchical markup document consists only of a set of differences between a hierarchical markup document in the set of hierarchical markup documents and a shared hierarchical markup document associated with the hierarchical markup document; and generating, based on the at least one difference document matching the remaining portion of the query path expression, a query result for the data query based on the at least one shared hierarchical markup document that partial matched the query path expression and the at least one difference hierarchical markup document.