WCF - A Perspective
.NET 3.0 has been made available to all the developers recently. With it comes a set of new set of API, which are simply there to unleash the .NET developer’s potential to create the next wave of powerful applications. These API, formerly called WinFX, take the form of four pillars – WCF, WF, WPF and WCS. In this post of mine, I would like to give a perspective on the Windows Communication Foundation (WCF).
Most typically, one starts off an introduction to WCF by explaining the four tenets of SOA, and how WCF embraces them from the ground-up. While this is very reasonable, I would like to think about WCF from a slightly different perspective which, of course, would eventually flow into confluence of the SOA tenets. To get a great insight into these tenets, I would urge you to look into this paper by the venerable Don Box.
WCF, in a nutshell, is all about facilitating message exchanges between endpoints. Note that ‘message’ and ‘endpoint’ are underlined. Well, these are but, what WCF is all about. These are concepts through which SOA is realized. Let me give you my understanding on these concepts:
If any entity needs to communicate with the world, it does so with Endpoints. Endpoint comprises of three elements (commonly called as ABC):
Address (Where) - Where can I find the service, the URI?
Binding (How) - How can I communicate with the service? What are security requirements, encoding requirements etc.?
Contract (What) – What is the structure of the messages that I need to communicate with the endpoint? What are the message exchange patterns (like Request/Reply, OneWay etc)
A WCF service would therefore, have at least one endpoint; it could have multiple based on different combinations of bindings, contracts or endpoint addresses.
If you really look at it, the concepts embodied by WCF aren’t new. They were pretty much present in ASMX. What lacked was that these concepts/abstractions were not explicitly codified in the ASMX (ASP.NET) framework. ASMX just seemed to be a quick way to get .NET classes to talk SOAP. So, caught in a world of classes and attributes, developers lost sight of underlying concepts that manifested as wsdl:portType, wsdl:port, wsdl:message and wsdl:binding.
WCF, on the other hand makes these concepts explicit, as seen in the ServiceEndPoint, Binding, ContractDescription, and EndPointAddress classes in the System.ServiceModel namespace. It is this object model that makes WCF very powerful. The number of out-of-the-box bindings available, and the existence of several extensibility points speak of the raw power of the WCF programming model. Also, this architecture is what makes unification of several programming models like MSMQ, COM+, WSE etc. possible.
“Message”, which can simply be thought of as the data/document/information exchanged between endpoints, is a first class citizen in the WCF programming model. Unlike its predecessor, where messages meant no more than an XML document (or stream) representing the SOAP envelope, WCF provides much better representation and finer control over messages. Messages are represented by the Message abstract class in the System.ServiceModel.Channels namespace.
Having seen how endpoints and messages are dealt with in WCF, it can be safely asserted that we are now consciously moving from the procedure call paradigm to a message exchange paradigm.
To find out more about WCF architecture, and the core classes that make up WCF, refer to this excellent paper by Yasser Shohoud.
As a part of the community launch of Windows Vista and Office 2007 in the B.NET User Group, we, a group of MVPs and other active community members authored a small e-book, comprising of articles on Vista, .NET 3.0 and Office 2007. Based on this post of mine, I wrote an article on what I thought the underpinnings concepts of WCF were. You could download the PDF of the e-book here.