1. Upload JDBC Driver You have to make JDBC drivers (e.g. mysql-connector-java-3.0.11-stable-bin.jar) for your database available to Oracle Application Server. You have to copy those to %ORACLE_HOME%/j2ee/home/applib directory.
2. Create a Native DataSource
You can use the ASC to create a native data source as follows:
description="Native DataSource" data-source-class="com.mysql.jdbc.jdbc2.optional.MysqlDataSource"
Now you should be able to access the DataSource connecting to MySQL database with a JNDI location "jdbc/MyDS".