From version 4.0 cattaDoc required MySQL 5.0 or higher. With cattaDoc version 5 MySQL 5.6 or higher is required in order to support full-text search. Previous versions of MySQL can no longer be used with cattaDoc.
Documents and files are not stored in MySQL, but in the cattaDoc server´s file system, in socalled repositories. cattaDoc maintains pointers in the database to the documents and files i the repositories.
MySQL was first acquired by Sun Microsystems and then Oracle, but you can still download the free open source MySQL database from www.mysql.com, the socalled Community Edition.