Cancel Journal Data through scripting

Hi all: because of DB size limitation, I need to implement a mechanism, other than the prune, to clear data by size, to keep the DB size within a certain threshold. The system.alarm.* set of function seem not to be usefull for this purpose, so I believe the only way is to delete data from the Journal DB tables, correct? And if so, where could I find documentation on how are the various dbo.alarms_* tables related one each other?
Many thanks in advance,