Policy processing model

Example embodiments provide for processing policies that include policy assertions associated with incoming or outgoing messages of an application in a distributed system, without having to have code within the application for executing the policy assertions. When a message is received by a Web service engine, a policy document associated with an application may be accessed for identifying objects corresponding to policy assertions within the policy document. The objects identified can then be used to generate assertion handlers, which are software entities that include executable code configured to determine if messages can satisfy requirements described by the policy assertions.