DISTRIBUTING APPLICATIONS WITH XML-RPC
The ability to integrate applications and distribute work increases as 
organizations take advantage of networking technologies. Customers and 
partners are information-hungry and often look more seriously at 
companies that can provide better data, more data, and more real-time 
access to the data than firms that don't provide such services. A new 
protocol called XML-RPC is designed to help meet the distributed 
integration needs of these customers. In this week's XML TechMail, 
we'll look at this new protocol and how it might be able to help your 
organization.

OVERVIEW
XML-RPC is a new protocol that uses common technology, including 
Hypertext Transfer Protocol (HTTP) and eXtensible Markup Language 
(XML), to provide access to data in remote systems across a network. 
The goal is to create technology that is simple to understand and easy 
to use while sharing data among disparate and complex applications. 
Because HTTP is the common protocol used by Web browsers and Web 
servers to communicate, it is quite common and generally understood by 
most organizations. XML, obviously a top choice for describing complex 
structured data using a text-based document, is also easy to 
understand.

REMOTE PROCEDURE CALLS
The "RPC" in XML-RPC stands for Remote Procedure Call, which is 
technical jargon for accessing the data in a networked application. 
This is a technology used commonly by other networked applications such 
as databases and operating systems. The procedure is defined by an XML-
RPC request. The request contains information that specifies what 
procedure to call and what kind of data to pass to it. You can think of 
this as a normal function call as used in any other programming 
language. For example, you might pass a username and password to a 
login procedure or a complete order to a commerce system. The data is 
sent to the procedure, and the procedure's return value is sent as an 
XML-RPC response back to the calling application.

XML
The basis of XML-RPC is the XML-RPC document type. This grammar 
specifies the format for both the XML-RPC request and the XML-RPC 
response. Each request document is sent as an HTTP request to a server 
that handles the XML-RPC protocol. The HTTP request is a standard HTTP 
POST request. The POST data is the XML document containing the XML-RPC 
request information. Within the request document are the parameters 
that define what procedure to call and what arguments to pass to that 
procedure.

Once the request is made and the remote procedure has been called, the 
return value from the procedure is packaged into an XML-RPC response. 
This response is sent back to the calling program as an XML document. 
The XML document is actually sent as the content of the HTTP response. 
In addition to the return value, the XML-RPC response might also 
contain "fault" data, which is information regarding errors during the 
process of calling the remote procedure.

SUMMARY
With XML as the data format of choice and HTTP as the network protocol 
of choice, XML-RPC provides a simple implementation for accessing data 
across different systems. XML-RPC uses a clean approach based on the 
HTTP request-response model and the use of XML to represent both the
request and the response. This technology helps reduce the complexities 
of integrating applications essentially to a Web page request.

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