To implement EJB 2.0 persistence (CMP2.0), JOnAS relies on the JORM framework (see http://jorm.objectweb.org/index.html). JORM must adapt its object-relational mapping to the underlying database and makes use of adapters called "mappers" for this purpose. Thus, for each type of database (and more precisely for each JDBC driver), the corresponding mapper must be specified in the DataSource properties file. This is the purpose of the datasource.mapper property.
The JORM database mapper named datasource.mapper has the following possible values:
rdb: generic mapper (JDBC standard driver ...)
rdb.postgres: mapper for PostgreSQL
rdb.oracle8: mapper for Oracle 8 and lesser versions
rdb.oracle: mapper for Oracle 9
rdb.mysql: mapper for MySQL