Protocol Buffers

http://code.google.com/p/protobuf/
https://developers.google.com/protocol-buffers/docs/overview
http://www.ibm.com/developerworks/cn/linux/l-cn-gpb/

Protocol Buffers are a way of encoding structured data in an efficient yet extensible format. Google uses Protocol Buffers for almost all of its internal RPC protocols and file formats.