CLEANING UP WITH SOAP
The Simple Object Access Protocol (SOAP) is an XML application for 
implementing distributed access to object-oriented models. SOAP is 
designed to allow applications to access remote objects on a network. 
This week's XML tip will highlight some of the features of SOAP.

GOOD CLEAN GOALS
SOAP is intended to provide access to remote objects, applications, and 
servers across a network using a simple protocol based on XML. Using 
XML affords SOAP the ability to perform across multiple platforms 
without modification. SOAP is designed to take advantage of many 
current technologies, including XML and HTTP. Additionally, SOAP is 
aimed at providing resource management through remote garbage 
collection and object references.

MESSAGE ORIENTED
SOAP is a message-oriented protocol. It is not designed solely for 
object-oriented applications; however, its messaging architecture lends 
itself to a client-server-based object model quite easily. The 
messaging framework essentially defines an envelope, or wrapper, around 
a message. The envelope contains information about the message and how 
it should be processed.

REQUEST-RESPONSE MODEL
Because SOAP uses the HTTP application protocol for communication, it 
is based on the HTTP request-response model. Each SOAP request is 
processed as an HTTP POST request. The SOAP data is contained in the 
POST content as XML. The XML contains the SOAP envelope, which encloses 
the SOAP request message. Once a request has been processed, the server 
will respond via HTTP. The HTTP response content will include a SOAP 
envelope with the response message.

APPLYING SOAP
One of the applications of SOAP is to provide access to some of the 
common object technologies currently available. These include 
Microsoft's Component Object Model (COM) and OMG's Common Object 
Request Broker Architecture (CORBA). These two competing object 
technologies each use their own "wire protocol" for accessing objects 
on remote servers. Using SOAP, an application developer can easily 
bridge from one architecture to another. SOAP provides the underlying 
messaging protocol for a client-server object scenario. Once a request 
is made from a client to a server, the server can access COM objects, 
CORBA objects, SQL databases, or some combination of these items in 
order to create the response. In addition, because SOAP is based on 
open, cross-platform standards such as HTTP and XML, it is extremely 
cross-platform compatible.

MORE INFORMATION
There are many places online where you can find out more about SOAP. 
The best resource is the current working draft available from the 
Worldwide Web Consortium (W3C).
http://www.w3.org/TR/SOAP/

The Microsoft Developer Network also has information and resources for 
SOAP developers available on its Web site.
http://msdn.microsoft.com/soap/

SUMMARY
The Simple Object Access Protocol is a new working draft from the W3C 
designed to give developers more robust and cross-platform access to 
remote objects. SOAP is a client-server oriented request-response-based 
protocol. With SOAP, developers can access objects using conventional 
HTTP protocols.

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