1. A virtual machine for executing a program, comprising: an instruction executor for executing instructions from the program using a computer, wherein: the instructions from the program have been generated in an intermediate language, by a compiler, to cause processing of an execution sequence according to a specification of a model, the model specification encoded using a model notation that is distinct from the intermediate notation; the instructions from the program are encoded in a markup language notation by the compiler and are selected by the compiler from allowable instructions of the intermediate language, the markup language notation being distinct from the intermediate language; and the allowable instructions of the intermediate language comprise: an event instruction for receiving an inbound event; an assignment instruction for assigning a value; a branch instruction for conditional transfer to a different one of the instructions; an emit instruction for specifying that an outbound event is to be emitted; a terminate instruction for specifying that a current execution context object is to be terminated; and a fan-out instruction for at least one of specifying event correlation and enabling a context switch, the context switch causing a particular execution context object to be used as the current execution context object.