Definition of internal structure
You can specify an undefined internal structure for an opaque data type with a server implementation in C or Java™.
The internal structure of the opaque data type is not known to the database server. The support routines you define for the opaque data type operate on the internal structure.
If you define the internal structure of your opaque data type to BladeSmith, BladeSmith generates useful code for it. If you do not specify the internal structure, BladeSmith generates code that operates as if your opaque data type is a stream of bytes.