The internal structure

To create an opaque data type, you must first provide a data structure that stores the data in its internal representation. This data structure is called the internal structure of the opaque data type because it is how the data is stored on disk. The support functions that you write operate on this internal structure; the database server never sees the internal structure. You create the internal structure as a data structure in the external language.

You can define an internal structure that supports either a fixed-length opaque data type or a varying-length opaque data type.