Advanced web service features are enabled and configured using a mechanism defined by the Web Services Policy Framework (WS-Policy) specification. A web service expresses its requirements and capabilities via policies embedded in the service's WSDL description. A service consumer verifies it can handle the expressed requirements and, optionally, uses server capabilities advertised in policies.

Technologies like Reliable Messaging, Addressing, or Secure Conversations, provides a set of policy assertions it can process. Those assertions provide the necessary configuration details to the Metro run-time to enable proper operation of these features used by a given web service. The assertions may specify particular configuration settings or rely on default settings that are pre-determined by the specific technology. For instance, in the snippet shown below, wsrm:AcknowledgementInterval and wsrm:InactivityTimeout are both optional and could be omitted. The following is an XML snippet showing WS-Policy assertions for WS-Addressing and WS-Reliable Messaging:

<wsp:Policy wsu:Id="AddNumbers_policy">
  <wsp:ExactlyOne>
    <wsp:All>
      <wsaw:UsingAddressing/>
      <wsrm:RMAssertion>
        <wsrm:InactivityTimeout Milliseconds="600000"/>
        <wsrm:AcknowledgementInterval Milliseconds="200"/>
      </wsrm:RMAssertion>
    </wsp:All>
  </wsp:ExactlyOne>
</wsp:Policy>

					

This snippet would be equally valid in either a WSIT configuration file or a web service's WSDL document.