The MonetDB kernel supports creation of user defined types, e.g. geometric types. relationship between SQL and MAL world is expressed using an external name.
CREATE TYPE [schema_name '.'] type_name EXTERNAL NAME type_identification DROP TYPE [schema_name '.'] type_name [RESTRICT | CASCADE]
The implementation of new atomary types is best postponed until there is no other performance-wise acceptable solution. Addition of an atomary type in the kernel would be beneficial if it is also complemented with bulk-operations and when type specific optimizers could exploit their semantics.