Implementing federated database systems by compiling SchemaSQL

Federated systems integrating data from multiple sources must cope with semantic heterogeneity by reasoning over both the data and meta-data of their sources. SchemaSQL is one of a number of related higher-order languages, which have been proposed for succinctly expressing integrated views over heterogeneous sources. We define a method for compiling SchemaSQL into standard SQL. We show that the output of the compilation algorithm is of size O(m+p) where m is the size of the catalogs and p the size of input queries. The resulting code may be executed by existing conventional SQL query engines without modification. We extend our basic compilation method by including type driven optimizations which, empirical evaluation shows, yield an effective execution by native query engines. Prior efforts do not provide feasible guarantees on the size of the compiled programs or require the development of new query engines encompassing higher-order query operators.