WCF



Overview


Building a distributed system is a very common task for many programmers. However, doing so involves
confronting numerous design challenges. In this chapter, you will review two key aspects of many distributed
systems (interfaces and XML web services), followed by an overview of Service-Oriented Architectures
(SOAs). Also, you will survey several core distributed APIs found within the Windows OS.
With this historical background in place, the remainder of this chapter will introduce you to the Windows
Communication Foundation (WCF) API. Here you will learn about the problems WCF attempts to solve,
study the ABC’s (addresses, bindings, and contracts) of building a WCF application, and explore some
common WCF development tools.
The information presented here will function as the backbone for the remainder of the class.

A Working Definition of Windows Communication Foundation (WCF)

To begin your examination of WCF, you will start with a review of common distributed programming
practices and previously distributed APIs. This is important, given that WCF leverages many of the
distributed concepts / APIs you may have used in the past.

WCF is a .NET 3.0 (and higher) API that allows you to build distributed systems. WCF is unique in that you
can select from many types of bindings. This fact alone makes WCF a very flexible framework. A single WCF
service could be exposed via an HTTP binding for outwardly facing callers or via a TCP binding for in-house
callers. The underlying plumbing details can be relegated to *.config files, which make it very simple to change
bindings and other details on the fly.

WCF makes extensive use of interface-based programming techniques. When you define a WCF service, you
typically begin by defining the interfaces that model the functionality callers can expect to find. These .NET
interfaces could be used by the runtime to generate WSDL definitions based on your choice of bindings.

In addition, WCF makes heavy use of .NET attributes to qualify how the runtime should handle client /
service interactions. Similar to the .NET remoting layer / XML web services, WCF attributes are used to
control data formatting, binding operations, and more. Recall that attributes are essentially code annotations.
Attributes are useless unless another piece of software reflects over them.  In this case, the ‘other piece of
software’ could be the WCF runtime as well as WCF development tools.

WCF is heavily influenced by XML web services and Service-Oriented Architectures (SOAs) in general. Like
an XML web service, WCF services make use of contracts and explicit boundaries and support the use of
various WS-* specifications.

However, a WCF service does not have to use web-service-centric bindings. If you wish, you can opt for P2P
bindings, named pipes, TCP bindings, and so on. The underlying binding is decoupled from the service itself. 
Therefore, changing bindings on the fly is very straightforward.

In a nutshell, as of .NET 3.0 (and higher), WCF is the preferred way to build new distributed systems. The
original distributed .NET APIs (System.Runtime.Remoting, System.Web.Services, and so forth) are still
supported. Furthermore, Visual Studio still has templates for ‘traditional’ ASP.NET web service project
workspaces.

It is also possible to migrate existing XML web services / remoting applications into the WCF programming
model. Doing so, however, may offer little benefit. In fact, it could entail a good amount of work.

This course does not cover migrating existing distributed systems into the WCF programming model. The
class assumes you intend to build new WCF services, hosts, and clients. However, Appendix A illustrates
how to interact with legacy COM+ components. You can read Appendix A if time / interest permits.

The .NET Framework SDK documentation provides details of migrating existing systems. If you are
interested in migrating from .NET remoting to WCF, look up the article ‘From .NET Remoting to the
Windows Communication Foundation (WCF)’. If you are interested in migrating from ASP.NET web
services to WCF, look up the article ‘Migrating ASP.NET Web Services to WCF’.

Finally, be aware that this class will focus on the core aspects of the programming model, which will be
commonplace to all of your WCF projects. Consult the .NET Framework SDK documentation for WCF
topics not addressed in this course. The WCF section of the SDK documentation provides a number of
excellent code examples, white papers, and tutorials.  Simply look up the Windows Communication
Foundation selection of the help system and dive in.
WCF Tutorial

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