WS-Policy Tutorial

Web service contracts can be extended with policies that express additional constraints, requirements, and qualities that typically relate to the behaviors of services. You can create human-readable policies that become part of a supplemental service-level agreement, or you can define machine-readable polices that are processed at runtime.


Name Spaces and prefix

* xmlns:wsp="http://www.w3.org/2006/07/ws-policy" – This represents the actual namespace used for elements from the WS-Policy language.

xmlns:wsam="http://www.w3.org/2007/05/addressing/metadata" –
We will show some policy examples related to the WS-Addressing
language, which is why this namespace comes up here. How the referenced
WS-Addressing features actually work is covered in Chapter 18 and this particular policy assertion is further revisited at the end of Chapter 19.

* xmlns:wsrmp="http://docs.oasis-open.org/ws-rx/wsrmp/200702" –
This namespace corresponds to the WS-ReliableMessaging policy
assertion. Although WS-ReliableMessaging is not a technology covered in
this book, there are a few references to one of its policy assertions
in the examples.

* xmlns:wsu="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-utility-1.0.xsd" –
There is a special type of schema that is referred to as a "utility
schema" in which generic and commonly used attributes are established.
One such attribute is wsu:Id, a
simple ID used to associate an identifier with an element. This and
other chapters make occasional reference to this attribute.



There are two ways of attaching policies to WSDL documents:

• The policy expression code can be embedded within the WSDL definition and then utilized via native references that can be attached directly to WSDL elements as child extensibility elements.
  

• Policy expressions can reside externally in a separate WS-Policy definition document, which is then referenced within the WSDL document via an external attachment mechanism.
  

Policy Attachment Points and Policy Subjects

Whatever part of a WSDL definition we attach a policy to is referred to as a policy attachment point. For example, we could have a policy attached to an operation element and then another to one of that operation's message elements.

Within WSDL 1.1, the following elements represent common policy attachment points:

• service element
• port element
• binding element
• portType element
• operation element
• message element

The policy attachment specification organizes these policy attachment points into the following four distinct policy subjects:

• Service (maps to service element in wsdl)
• Endpoint (maps to port, binding, portType)
• Operation (maps to Operation element in wsdl)
• Message

Note: This is work in progress more updates to follow

source:Thomas Erl- Web service Contract Design and versioning for SOA