Fixed-Length Opaque Types
A fixed-length opaque type has an internal structure of fixed size.
To create a fixed-length opaque type, specify the size of the internal
structure, in bytes, for the INTERNALLENGTH modifier. The next example
creates a fixed-length opaque type called fixlen_typ and allocates
8 bytes for storing this data type.
CREATE OPAQUE TYPE fixlen_typ(INTERNALLENGTH=8, CANNOTHASH)