A pervasive system features a plethora of devices, services and applications organized as a large distributed system. One approach to managing such systems is by policies where administrators specify the management action to be taken in different situations using Event-Condition-Action (ECA) rules. An important problem with policy-based management of a pervasive system is that multiple rules can get triggered on a single event and the behavior of the system depends on the order of rule enforcement. Systems managed using ECA policies do not provide guarantees about system behavior when multiple rules are concurrently triggered. In this paper, we present a novel rule framework called Event-Condition-Precondition-Action-Postcondition (ECPAP) that combines axiomatic specifications with ECA rules for specifying management rules. ECPAP rules contain action specifications in first-order predicate logic that enables us to reason about the enforcement order. We define a notion called enforcement semantics for policy-based management and show how this can be used to provide guarantees about system behavior. We present the details of the framework.