Among other things, we describe a computer-implemented method, performed by a data processing system, of executing a computer program based on a query that is expressed in accordance with a query language applicable to a relational database, the computer program executed based at least in part on data stored in a tangible, non-transitory computer-readable medium, the executing including receiving a SQL query, where the SQL query includes an identifier associated with a resource that is external to the data processing system, generating a computer program based on the SQL query, and executing the computer program, causing transmitting one or more instructions to the resource, the instructions defining operations other than operations of the SQL query, and receiving data from the resource in response to the instructions.