1.1 History


Web services didn't spring full- formed from the collective forehead of Microsoft, IBM, and Sun. Systems such as SOAP, XML-RPC, and WSDL are merely the latest iteration in a long series of distributed computing initiatives. Ever since there were two computers, people have been trying to make them work together.

The web services we have today trace their ancestry back to the Sun Remote Procedure Call (RPC) system. This provided a standard way for a client to interact with a server, using the model of a procedure call. A server might offer many services (procedures, identified by name ), and a client would tell the server which service to use and what values to pass it (parameters). The server would send back a value (the return value) from the service.

The problem at the time was that the binary representation of values varied depending on the operating system, hardware, and programming languages that created the value. The Sun RPC system solved the problem by specifying how to encode the values in the parameters ”a standard binary format. Representing data can still be a problem, but webservers solve it by representing values in XML (Extensible Markup Language).

Microsoft offered the next major step forward, with its Component Object Model (COM). COM was based on language independence, interoperability, a strong focus on reusable components, and extensibility. The ability to develop components and object libraries that would be accessible over varying platforms and by multiple languages removed some old hurdles in areas of rapid application development and system integration. While RPC dealt only in procedures, COM was designed to exist in a world of objects and method calls.

Microsoft extended this model with DCOM, the Distributed Component Object Model. DCOM overcame many of the limitations of data and interface specifications. Remote objects could be accessed as though they were local, and you could even extend a remote interface. DCOM has never really taken off outside the Microsoft world, though.

The leading competitor to DCOM (and its successor, COM+) is the Common Object Request Broker Architecture, known as CORBA. Also object-oriented, CORBA has recognition and acceptance at high levels within large-scale development projects. At the heart of a CORBA implementation is an Object Request Broker (ORB), which takes incoming requests and dispatches them to the appropriate server. Programmers use the Interface Design Language (IDL) to describe the functions that a service offers, and then a translator program takes the IDL and emits source code to handle the interaction with the ORB.



Programming Web Services with Perl
Programming Web Services with Perl
ISBN: 0596002068
EAN: 2147483647
Year: 2000
Pages: 123

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