I see that the metadata/type-mapping is optional in -ds.xml and the defaults/datasource-mapping is also optional in standardjboss-cmp.xml.

Looking at the code the type-mapping is obtained from one of these 3 places.
1. user defined in jbosscmp-jdbc.xml
2. defaults/datasource-mapping in standardjboss-cmp.xml
3. TypeMappingMetaData from the datasource metadata mbean.

If 2 and 3 are optional and the user does not define 1 how is the type-mapping obtained?

Also without the metadata/type-mapping in -ds.xml the TIMERService doesn't start up.