Webservice development Styles

Webservices can be developed in any of following two ways.

1. Contract-First
The artifacts of external world - WSDL (web service description language) and other schema references are created first and these config definitions are implemented in any of the programming languages (java,.net etc) afterwards.


2. Contract-Last
Here actual services are coded in any of the programming languages and the XML artifacts(wsdl) are created based on the prgrammed services.

Example
For example, Spring web service supports Contract First style whereas web service development from any of IDEs (RAD etc) encourages coding first and generates contract based on the programmed services.

Which is good?
Lets assume the webservices are implemented in Java, the basic difference between these two styles are whether XML is generated from java or Java is genereated from XML.

There is a fundamental difference between hierarchial languages such as XML and object oriented language as Java. Following factors advocates Contract-First better than of Contract-Last atleast from java perspective.

1. Unportable Types:
Few Java types such as TreeMap cannot be converted directly to XML.
2. Cyclic Graph:
Class A refers B and B refers back A. Its difficult to handle these scenarios in XML whereas its very common in java which makes Contract-Last (java->xml) tougher.
3. Reusability:
The XML configurations can be defined in individual XSD files and can be imported to WSDL so that these individual XSD configurations can be reused if required in any other WSDL files.