App Engine - why are there PhoneNumber, Link, Rating etc classes?

Question

I haven't found any reason for the existence of a few of the App Engine classes. There's a PhoneNumber, a Link, a PostalAddress, a GeoPt, a Rating, etc. Why are these given special treatment? They don't seem to have any smarts - e.g. geo searching. I know Link has more space than a String property, but the rest?

See: http://code.google.com/appengine/docs/java/datastore/dataclasses.html

Answer 1

Those types are 'semantic' types. They're present in the Java API for parity with the Python API. In the Python API, they define special behaviour with regards to the .to_xml() method - for example, a PhoneNumberProperty serializes like this:

<property name="foo" type="gd:phonenumber"><gd:phoneNumber>12345-678</gd:phoneNumber></property>