Clean up your wire protocol with SOAP, Part 1
An introduction to SOAP basics
Many developers have run into this dilemma: A CORBA client needs to obtain the services of a Distributed Component Object
Model (DCOM) client or vice versa. The common solution is to use a COM/CORBA bridge, however, this answer is fraught with
failure points. Suppose you have just introduced a complex new piece of software in the midst of two already complicated pieces
(the CORBA ORB and the COM infrastructure). The bridge's complexity results from the intricate back-and-forth translation
that it must complete from CORBA's Internet Inter-ORB Protocol (IIOP) to DCOM's Object Remote Procedure Call (ORPC). Any changes
to these protocols mean changes to the bridge. What if I tell you that SOAP can alleviate the problem? Interested?
SOAP stands for Simple Object Access Protocol. In a nutshell, SOAP is a wire protocol similar to the IIOP for CORBA, ORPC
for DCOM, or Java Remote Method Protocol (JRMP) for Java Remote Method Invocation (RMI). At this point you may be wondering,
with so many wire protocols in existence, why do we need another one. In fact, isn't that what caused the problem discussed
in the opening paragraph in the first place? Those are valid questions, however SOAP is somewhat different from the other
Let's examine how:
- While IIOP, ORPC, and JRMP are binary protocols, SOAP is a text-based protocol that uses XML. Using XML for data encoding
gives SOAP some unique capabilities. For example, it is much easier to debug applications based on SOAP because it is much
easier to read XML than a binary stream. And since all the information in SOAP is in text form, SOAP is much more firewall-friendly
than IIOP, ORPC, or JRMP.
- Because it is based on a vendor-agnostic technology, namely XML, HTTP, and Simple Mail Transfer Protocol (SMTP), SOAP appeals
to all vendors. For example, Microsoft is committed to SOAP, as are a variety of CORBA ORB vendors such as Iona. IBM, which
played a major role in the specification of SOAP, has also created an excellent SOAP toolkit for Java programmers. The company
has donated that toolkit to Apache Software Foundation's XML Project, which has created the Apache-SOAP implementation based
on the toolkit. The implementation is freely available under the Apache license. Returning to the problem stated in the opening
paragraph, if DCOM uses SOAP and the ORB vendor uses SOAP, then the problem of COM/CORBA interoperability becomes significantly
SOAP is not just another buzzword; it's a technology that will be deeply embedded in the future of distributed computing.
Coupled with other technologies such as Universal Discovery, Description, and Integration (UDDI) and Web Services Description
Language (WSDL), SOAP is set to transform the way business applications communicate over the Web with the notion of Web services.
I can't emphasize enough the importance of having the knowledge of SOAP in your developer's toolkit. In Part 1 of this four-part
series on SOAP, I will cover the basics, starting with how the idea of SOAP was conceived.