1. A method in a first computer system, comprising: associating a first data type with a request for a resource, the first data type being an open data type that includes a plurality of properties; transmitting the request for the resource to a second computer system, the resource being instantiated at the second computer system according to a second data type that includes the plurality of properties and an additional property; receiving the resource from the second computer system; materializing the received resource into an instance of the first data type, the materialized instance of the first data type including a plurality of name/value pairs corresponding to the plurality of properties and a name/value pair associated with the additional property; and storing the instance of the first data type in a database, said storing including storing the name/value pair in the database as an extension property to the open data type.