1. At a computer system including a processor and a memory, in a computer networking environment including a plurality of computing systems, a computer-implemented method for implementing one or more custom operators in a query for a parallel query engine, the method comprising: an act of receiving a portion of partitioned input data at a parallel query engine, wherein the parallel query engine is configured to process data queries in parallel, the queries including a sequence of built-in operators; an act of incorporating at least one custom operator into the sequence of built-in operators for a query; an act of accessing the sequence of operators to determine how the partitioned input data is to be processed, wherein the at least one custom operator is accessed in the same manner as the built-in operators; and an act of processing the sequence of operators including both the built-in operators and at least one custom operator according to the determination indicating how the data is to be processed.