A type mapping tells JAWS how to map java objects to a specific database. For example, some databases have a boolean type, and other don't, so you have to map a java.lang.Boolean to a CHAR(5).
Many type mappings are already defined in standardjaws.xml. If you want to define a new one, I advise you to modify one of these: copy it and paste it to the <type-mappings> section of your jaws.xml file.
A type mapping is constituted of several mappings, one for each java Class that you need to map. If your class is not found in the mappings, JAWS will use the mapping for java.lang.Object.
A mapping comes in 3 parts:
the <jdbc-type> is the jdbc type to use. Its value must be one of the fields of java.sql.Types (e.g. BIT, CHAR...). This jdbc type will be used by JAWS to determine which method to call on PreparedStatement and ResultSet for INSERT / UPDATE / SELECT queries.
If the type mapping we provide for a particular database is faulty and you find you have to modify it, please consider sharing your changes: post the modified mapping on the jbosscmp mailing list.