Windows Communication Foundation

• Entity boundaries are explicit with underlying functionaility accessed via the exposed interface.
• Services are autonomous – hence published interfaces must remain unchanged
• Services are based on contracts, schemas and policies – all services require a contract regarding what is required to consume items from the interface (usually done through WSDL document) Along with a contract, schemas are required to define the items passed as parameters or delivered through the service (using XSD schemas). Finally policies define any capabilities or requirements of the service.
• Service compatiability that is based upon policy – enables services to decide policies, decided at ruyntime, that ar required to consume the service. These policies are usually expressed through WS-policy.

WCF is a framework that works on SOA principles and makes it relatively simple to implement. It is also a means to build distributed applications in a Microsoft environment, though the consumers of the application certainly don’t need to be Microsoft clients.

WCF allows you to build all kinds of distributed applications including 'traditional' Web Services so that your services support SOAP and will therefore be compatible with older .NET (and other) technologies. WCF is not just about pure SOAP over the wire - you can work with an Infoset, and create a binary representation of your SOAP message that can then be sent along with your choice of protocol. This is for those who are particularly concerned about performance and have traditionally turned to .NET remoting.

WCF can also work with a message through its lifecycle meaning that WCF can deal with transactions like those of Enterprise Services. Along with distributed transactions, WCF can deal with the queuing of messages, and it allows for the intermittent connected nature that an application might have to deal with.

WCF is all about messages but not just WebService like messages. For example, WCF can be used to communicate messages to components contained on the same machine on which the WCF service is running. Hence you can use WCF for communication between components contained in different processes on the same machine as well as with other components on another machine, whether that machine is a Microsoft OS based machine, or not.

WCF also enables you to develop a service once and then expose that service via multiple endpoints (which can use entirely different protocols) via simple configuration changes.