Hi Alonso,
The
database design for this module is really simple (just 3 tables). Just have a look at the tables starting with 'attendance' (assuming you've installed the module). Some of the complicated stuff like roles and capabilities (that are part of Core) are documented elsewhere in
MoodleDocs. See
http://docs.moodle.org/en/Development:Database_schema_introduction
Cheers,
Barry