10. 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: extracting implicit parallelism in a query in user code written in a native programming language; representing the implicit parallelism as a runtime representation including a set of tasks and a set of interactions of the set 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 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.
10. 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: extracting implicit parallelism in a query in user code written in a native programming language; representing the implicit parallelism as a runtime representation including a set of tasks and a set of interactions of the set 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 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. 13. The computer readable storage medium of claim 10 , wherein the dynamically selected execution runtime is one of a set of two or more execution runtimes in the computer system.