In C, ADBC consists of a self-contained header. The header is reproduced in full here, and is intended to be self-documenting.
From apache/arrow-adbc commit f044edf5256abfb4c091b0ad2acc73afea2c93c0:
.. literalinclude:: ../../../../format/adbc.h :language: c :linenos: :lineno-match: :lines: 166-1123