When you use a web service that's based in the cloud, your response is likely to be in JSON or XML, two standard formats for transmitting data between a server and web application. There will be times when you have a choice between the two formats, but other times you have to go with what you get.

The Google Geocoding Web Service, for example, does give you a choice.

If you want the response in XML format, you would use

http://maps.googleapis.com/maps/api/geocode/xml

If you wanted the response in JSON, you would use

http://maps.googleapis.com/maps/api/geocode/json?paremters

While similar in intent, how you get information out of XML and JSON data structures is quite different in execution.