http://www.drdobbs.com/web-development/restful-web-services-a-tutorial/240169069?pgno=1

Difference between PUT and POST

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-It is clear from the above table that a PUT request will not modify or create more than one resource no matter how many times it is fired (if the URI is same). There is no difference between PUT and POST if the resource already exists, both update the existing resource. The third request (POST http://MyService/Persons/) will create a resource each time it is fired. A lot of developers think that REST does not allow POST to be used for update operation; however, REST imposes no such restrictions.