Efficient XML Interchange (EXI)
Efficient XML Interchange (EXI) is a W3C standard for creating a compact binary representation of XML.
There were several design objectives for EXI, which included a desire to create a general purpose encoding method that might be used on a wide variety of systems, a method that requires minimal complexity, an efficient encoding, a flexible solution that can handle all valid XML, and a solution that is interoperable with existing XML technologies.
EXI provides several different encoding methods, including ones that creates a bit-aligned encoding, byte-aligned encoding, compressed encoding, uncompressed binary encoding, schema-informed encoding, "schema-less" encoding, etc. A complete list of options can be found here.
Resources: W3C EXI Working Group, XML Compression Results
See Also: Extensible Markup Language (XML)