1. A computer readable storage medium, which does not include transitory propagating signals, storing computer-executable instructions that, when executed by a computer system, cause the computer system to perform a method comprising: identifying a query syntax in user code written in a native programming language; translating the query syntax into a runtime agnostic representation of the user code that expresses tasks and the interactions of tasks without explicit reference to programming features or constructs of any particular execution runtime; dynamically selecting an execution runtime from at least two execution runtimes for executing the runtime agnostic representation that is executable with the dynamically selected execution runtime; and delineating a programming model for the user code from the at least two execution runtimes to permit the user code to target different execution runtimes of the at least two execution runtimes.