Continuing on with her series of tips for those building web services Lorna Mitchell has posted this new item to her blog looking at the importance of a version parameter in each call.

When designing a service API, there are lots of things you can do right, and plenty of pitfalls. Most of both of these are completely specific to the situation you are designing for but I have one tip that has helped me out in a number of scenarios: Include a version parameter with every method call.

She recommends this parameter for a single reason - you can modify the API, even existing functionality and, based on that value, know which version of the action the user's looking for. This enabled you to make improvements and updates to the service without requiring all of your users to have to recode everything - they have the choice to update or not.