Data Format Description Language (DFDL)
This working group has defined the Data Format Description Language (DFDL), for describing the structure of binary and textual files and data streams so that their format, structure, and metadata can be exposed.
The Official PDF of the DFDL v1.0 Specification is now an Open Grid Forum "Recommendation".
You can also view an HTML page of the DFDL v1.0 Spec.
DFDL v1.0 is based on XML Schema but DFDL is not strongly tied to XML. Implementations can convert data from native form into a variety of representations including JSON, XML, EXI, SAX-style event callbacks, DOM-trees, etc.
This working group maintains this standard and proposed extensions/additions to it.