Quickview to my thoughts:
WCF and SOA
1.
Client
User Interface Layer
ASP.NET web application/windows forms based application/WPF or WPF/e(XBAP). User interface validation is built into this tier and mapped to the specific client UI form, or optionally inside a validation business rules assembly shared with the application server tier.
2. Service Agent Layer
The Service Agent Layer is the proxy to Application Server components. Service Agent components manage the protocol and security details of the services, so the client logic is decoupled from the underlying WCF interfaces. The Service Agent interacts with the technical architecture where necessary for services like security and instrumentation.
3. Application Server
The overall responsibility of the Application Server Layer is to perform the business logic and data access operations on behalf of the client application.
a. WCF Service Layer
Service contract, message contract and data contract exposed to clients to interface with the Application Server Tier.
b. Business Logic Layer
The Business Logic layer contains the core business logic for a particular business function. Business Logic methods encapsulate all the necessary logic, calling data access methods. All business logic components implement service contract interfaces.
c. Data Access Layer
Data Access Layer (DAL) components encapsulate connectivity and persistence details of accessing a particular back-end data source from higher level components.
References:
MSDN link to Web Service Factory.
Tried the guidance package, it's useful.