Why Web Services?

Web Services Building Blocks

The following graphic shows the core building blocks needed to facilitate remote communication between two applications.

Let's discuss the purpose of each of these building blocks. Because many readers are familiar with DCOM, I will also mention the DCOM equivalent of each building block.

  • Discovery The client application that needs access to functionality exposed by a Web service needs a way to resolve the location of the remote service. This is accomplished through a process generally termed discovery. Discovery can be facilitated via a centralized directory as well as by more ad hoc methods. In DCOM, the Service Control Manager (SCM) provides discovery services.

  • Description Once the end point for a particular Web service has been resolved, the client needs sufficient information to properly interact with it. The description of a Web service encompasses structured metadata about the interface that is intended to be consumed by a client application as well as written documentation about the Web service including examples of use. A DCOM component exposes structured metadata about its interfaces via a type library (typelib). The metadata within a component's typelib is stored in a proprietary binary format and is accessed via a proprietary application programming interface (API).

  • Message format In order to exchange data, a client and a server have to agree on a common way to encode and format the messages. A standard way of encoding data ensures that data encoded by the client will be properly interpreted by the server. In DCOM, messages sent between a client and a server are formatted as defined by the DCOM Object RPC (ORPC) protocol.

    Without a standard way of formatting the messages, developing a toolset to abstract the developer from the underlying protocols is next to impossible. Creating an abstraction layer between the developer and the underlying protocols allows the developer to focus more on the business problem at hand and less on the infrastructure required to implement the solution.

  • Encoding The data transmitted between the client and the server needs to be encoded into the body of the message. DCOM uses a binary encoding scheme to serialize the data contained by the parameters exchanged between the client and the server.

  • Transport Once the message has been formatted and the data has been serialized into the body of the message, the message must be transferred between the client and the server over some transport protocol. DCOM supports a number of proprietary protocols bound to a number of network protocols such as TCP, SPX, NetBEUI, and NetBIOS over IPX.



Building XML Web Services for the Microsoft  .NET Platform
Building XML Web Services for the Microsoft .NET Platform
ISBN: 0735614067
EAN: 2147483647
Year: 2002
Pages: 94
Authors: Scott Short

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