1. A computer-implemented method comprising: rewriting an original query into a rewritten query, said original query including: a first path-based expression that evaluates to first one or more values, and a second path-based expression; wherein the rewritten query includes a first rewritten expression that causes the first one or more values to be computed using streaming evaluation; wherein the rewritten query includes a second rewritten expression that corresponds to said second path-based expression; computing the first rewritten expression using a streaming evaluation; computing the second rewritten expression using XML index evaluation of an XML index that indexes nodes in a collection of XML documents, wherein each index entry of entries of said XML index contains location data that identifies a location of an element within a representation of an XML document of said collection of XML documents; wherein the second rewritten expression evaluates to an output for location information within a representation of a particular XML document, wherein said output of said second rewritten expression is an input to said first rewritten expression; wherein said location information is derived from location data from an entry in said XML index; and wherein computing the first rewritten expression includes using said location information to locate an element within said representation of said particular XML document using streaming evaluation.
1. A computer-implemented method comprising: rewriting an original query into a rewritten query, said original query including: a first path-based expression that evaluates to first one or more values, and a second path-based expression; wherein the rewritten query includes a first rewritten expression that causes the first one or more values to be computed using streaming evaluation; wherein the rewritten query includes a second rewritten expression that corresponds to said second path-based expression; computing the first rewritten expression using a streaming evaluation; computing the second rewritten expression using XML index evaluation of an XML index that indexes nodes in a collection of XML documents, wherein each index entry of entries of said XML index contains location data that identifies a location of an element within a representation of an XML document of said collection of XML documents; wherein the second rewritten expression evaluates to an output for location information within a representation of a particular XML document, wherein said output of said second rewritten expression is an input to said first rewritten expression; wherein said location information is derived from location data from an entry in said XML index; and wherein computing the first rewritten expression includes using said location information to locate an element within said representation of said particular XML document using streaming evaluation. 3. The method of claim 1 , wherein the first expression is in a SELECT clause and the second expression is within a WHERE clause.