1. An apparatus for enforcing a compliance requirement for a software application in execution in a virtualised computing environment, the apparatus comprising: an identifier adapted to identify a resource instantiated for execution of the application; a retriever adapted to retrieve a compliance characteristic for the application, the compliance characteristic being retrieved based on the identified resource and having associated a compliance criterion based on a formal parameter, the compliance criterion defining a set of compliant resource states; a first selector adapted to select a software component for providing an actual parameter corresponding to the formal parameter, the actual parameter being based on data concerning the resource; an evaluator adapted to evaluate the compliance criterion using the actual parameter; an application modifier adapted to, in response to a determination that the resource is outside the set of compliant resource states, the determination being based on the evaluation of the compliance criterion, modify the software application to a modified software application having associated a resource with a state belonging to the set of compliant resource states; and a detector adapted to detect a change to one or more of the resources, wherein the identifier, selector and evaluator are operable in response to a determination by the detector that one or more resources is changed, and wherein the selector selects the software component based on an identification of one or more data items that the software component is operable to provide.