dbiCal is a PHP database back end solution storing (multiple) iCal calendars in a database
Supporting ALL iCal calendar information; timezone, event, todo, journal and freebusy
components with all properties and parameters, including x-properties.
dbiCal may very well fit as a caldav calendar database back end.
Using the PHP PEAR MDB2 package as database API, dbiCal supports the following RDBMS:
MySQL/MySQLi, PostgreSQL, Oracle, Frontbase (unmaintained), Querysim, Interbase/Firebird,
MSSQL, SQLite. Depending on the underlying RDBMS (and MDB2), transactions are supported.
dbiCal is using iCalcreator as the calendar information API and, opt. pear Log.
Simple interface functions; insert, select, delete and calendar information.
Includes a web admin page, offering ability to upload, insert, examine (file),
inspect (db), removal and compare of calendar files.