1. A computer-readable storage medium storing computer-executable instructions for performing a method comprising: receiving a query that identifies a first input data source; identifying a query category for a first query operator in the received query; identifying a data source category for the first input data source; and generating a first results object based on the identified query category and the identified data source category, wherein the first results object supports at least one of random access and sequential access to results produced by the first query operator.