AGENGT <-----> AGENT

The Architectural Models
The four models are
Message Oriented Model
Service Oriented Model
Resource Oriented Model
Policy Model

1. Message Oriented Model focuses and explains Web services strictly from a message passing perspective



2. Service Oriented Model lays on top of and extends the Message Oriented Model in order to explain the fundamental concepts involved in service - in effect to explain the purpose of the messages in the Message Oriented Model.
The Service Oriented Model (SOM) focuses on those aspects of the architecture that relate to service and action.The primary purpose of the SOM is to explicate the relationships between an agent and the services it provides and requests. The SOM builds on the MOM, but its focus is on action rather than message.



3.Resource Oriented Model focuses on resources that exist and have owners.
The Resource Oriented Model focuses on those aspects of the architecture that relate to resources. Resources are a fundamental concept that underpins much of the Web and much of Web services; for example, a Web service is a particular kind of resource that is important to this architecture.





4 The Policy Model focuses on constraints on the behavior of agents and services.
Policies are about resources. They are applied to agents that may attempt to
access those resources, and are put in place, or established, by people who
have responsibility for the resource.






Web Services Architecture Stack




WSDL describes Web services starting with the messages that are exchanged between the requester and provider agents

SOAP 1.2 provides a standard, extensible, composable framework for packaging and exchanging XML messages


Source : http://www.w3.org/TR/ws-arch/