1. A computer-implemented method at a data storage system comprising: accessing, at a processor, a policy comprising one or more criteria to be applied to a flow of data storage input/output requests between endpoints of the flow, the endpoints comprising at least one computing entity and at least one store, wherein the at least one computing entity and the at least one store are associated with high-level identifiers; sending control instructions to at least one stage of the flow of data, the stage being a component of the data storage system through which the flow passes and which is configured to interpret the control instructions, the control instructions arranged to control a plurality of queues at the at least one stage in order to treat the flow of data storage input/output requests such that the policy is met; and resolving the high level identifiers into low level identifiers in order to process the control instructions at the at least one stage.