Originally posted 07/20/07 @ 12:47:55 pm
W3C has published the Web Services Description Language (WSDL) Version 2.0 Recommendation. That means we can talk about a new standard now.
From history, you can recall SOAP was not a standard by committee but a de facto one, and WSDL 1.1 was a member submission done by Microsoft and IBM. Seven years later, WSDL 2.0 comes to see the light.
I mentioned before in this blog that WSDL offered four types of messaging, a combination of style/encoding parameters. There was an RPC style, and a Document Style, and for a backward compatibility, RPC could be Encoded or Literal.
Also, WSDL allowed a extension to define the transport, but it was just to say we were going to use HTTP, and that to send a SOAP structure as its payload. It was fixed to use the POST method, and it was also fixed the headers contents and such. Not much flexibility.
Well, WSDL 2.0 changes that. It now offers only one style: document. With that you can simulate your RPC calls if you want. Also, it allows to define the content of the document using an XML Schema, but that doesn't mean you will be sending XML through the wire (more on this later)!
But it doesn't stop there. WSDL 2.0 expands significantly the HTTP binding spec. Now you can specify if using GET instead of POST, indicate if you want you parameters (defined in the schema in types, remember?) to be encoded in the URL! Even, you can indicate that you want multi-part messages!
How friendly is that to REST? Keep on reading...I know. Most of the REST community may hate anything that has to do with Web Services using its standards. But I feel that enterprise systems should not go in the wild with the REST complexity. Which complexity? you may say, if REST is the easiest thing. Well, yes and no. It is simple, but not easy. Everything has a complex component, and in REST it is the process of manually reading the contract and creating the interaction in code.
Yes, it is ok for simple parameter passing (two or three) even for some simple XML documents. But if you need to work with very complex XML and interactions, there may be a problem. Enterprise services may not be two or three parameters, and it may not be fine grained services. A way to describe all that so developers free themselves of understanding and coding XML to start thinking in business logic and processes, is a plus.
Will WSDL 2.0 that allows complex and simple things to be described, be a choice for that need of description? Who knows. What I know is that WSDL 2.0 seems to allow more Restful services descriptions, where they apply.
For more information about WSDL 2.0, please read the primer
For an article that explains Rest in WSDL 2.0 with more detail, please read this one from Eran
William Martinez Pomares.
Reference: WSDL 2.0 - a REST Friendly Language