Use WSDL for Web Services

You do not need WSDL for web services, if you know how to invoke the services. WSDL is useful in two ways: when you want to invoke a service you do not know, you need information like the methods and the methods’ signatures; secondly, WSDL plays a role exactly like IDL to bridge the different languages, i.e. different languages maps to WSDL and use SOAP for protocol. It is yet another tempt for people to provide a uniform interface over specific languages. This time, it is over HTTP and SOAP. It is easier to code than CORBA. But the complexity of using CORBA and using WSDL are comparable.

Because AXIS uses bean serializer to implement the types in WSDL, the SOAP message uses tages for the attributes and values of the objects (cf. my post on 7/22).

People can image, with additional layers of HTTP and SOAP, the web services are slower than RPC or RMI. Here is a link provided by Michael Sintek on the performance of different SOAP implementations. Hopefully the fastest JibxSoap is just a little bit slower than RMI. Well, it is difficult to say if the slow is significent or not. But it is rather faster than other SOAP implmentations. I cite: “The performance of the JibxSoap implementation is likely due to two factors. First off, the light-weight nature of the framework and efficient internal operation adds very little per-message overhead. This per-message overhead looks to be especially high with Axis (as shown by the poor performance of all the Axis versions at very low response density, where the number of messages exchanged is considerably larger than all the other test cases combined). Secondly, the JiBX data binding basis of JibxSoap allows very fast conversion between XML and Java objects, minimizing the overhead for larger messages.” It is also interesting to know that Sun wants to use binary data encoding to replace XML, in order to improve the web service performance.

Isn’t WSDL another tempt to provide a framework over specific languages? Do we always turn in circles?