Many organizations store and process data at different locations using a heterogeneous set of formats and data management systems. However, data analyses can often provide better insight when data from several sources is integrated into a combined perspective. DataCalc is an extensible data integration platform that executes ad-hoc analytical queries on a set of heterogeneous data processors. The platform uses an expressive function shipping interface that promotes local computation and reduces data movement between processors. In this paper, we provide a detailed discussion of the architecture and implementation of DataCalc. We introduce data processors for plain files, JDBC, the MongoDB document store, and a custom in memory system. Finally, we discuss the cost of integrating additional processors and evaluate the overall performance of the platform. Our main contribution is the specification and evaluation of the DataCalc code delegation interface.