by April 4, 2001 0 comments



The Internet is becoming more and more powerful each day, with websites now expected to perform almost all tasks that any desktop application would do. But these Web applications still depend on scripting languages that were designed to work within the limitations of HTML, which means that they offer very limited functionality. So, building next-generation Web app- lications using these technologies would be, at best, a Herculean task. Step in SOAP or Simple Object Access Protocol.

SOAP, an XML-based protocol that’s designed to help overcome these limitations, has been developed by a group of vendors led by Microsoft. This protocol lets you call an application, or an
individual object or method within an application, across the Internet. Any Web programmer would
realize how significant and powerful this can prove to be. Many of you may rightfully point out that this is nothing new. SOAP uses a combination of XML and HTTP to codify the existing practise of invoking methods remotely. This was earlier being achieved by using DCOM (Distributed Component Object Model), CORBA (Common Object Request Broker Architecture), or IIOP (Internet Inter ORB Protocol). SOAP provides a very ‘friendly’ method for an application on one computer to communicate with another application on another computer (quite possibly on a different platform).

In effect, SOAP lays down a standard for cross-platform communication between applications. One major advantage of SOAP-based applications over those based on traditional protocols like DCOM is that the former are not blocked by firewalls. Applications based on DCOM, etc, rely on dynamically assigned ports for remote method invocations. These, however, are generally blocked by firewalls, leaving them non-operational. Since SOAP uses HTTP, which by default works on port 80, applications based on it don’t suffer from this drawback as all firewalls have this port open. CIS (COM Internet Services) also use port 80, but are restricted to Windows-based systems.

The XML part of every SOAP message consists of three parts. 

  • The SOAP envelope (mandatory): This is the first part, which contains the element name, SOAP version, etc.

  • The SOAP header (optional): Adds characteristics to the SOAP message. 

  • The SOAP body (mandatory): The information to be processed by the endpoint.

  • SOAP is being proposed as a standard to the IETF (Internet Engineering Task Force). Currently, it’s being used in Microsoft’s .NET line of products. 

Kunal Dua

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