1. In a computing system a method in which one or more applications manage one or more transactions, each of which includes a plurality of activities to be executed when performing a transaction, and wherein the method provides for flexible composition of a transaction that is to be performed by allowing one or more actions of the transaction that is to be performed to be executed outside of a continuation based runtime, and one or more activities of the same transaction to be executed inside the continuation based runtime, the method comprising the following acts: initiating at a computing system an application which contains one or more transactions to be performed, with each transaction comprising one or more activities that require execution in order for the transaction to be completed; initiating at the computing system a continuation based runtime; initiating outside of the continuation based runtime a transaction of the application; performing one or more activities of the initiated transaction prior to enlisting service of the continuation based runtime; while performing the one or more activities of the initiated transaction outside of the continuation based runtime, encountering an activity that is to be executed within the continuation based runtime; and providing the encountered activity to the continuation based runtime and executing the encountered activity within the continuation based runtime.