This article is from the Object-Oriented Technology FAQ, by Bob Hathaway firstname.lastname@example.org with numerous contributions by others.
IDL is a schema definition language. Schema modifications are defined
in IDL, requiring ad-hoc offline transformations of the database, in
general. A simple class of transformations can be handled by
IDL->ASCII and ASCII->IDL translators (i.e., integer format changes,
list->array, attribute addition).
[conversation with Ellen Borison of Persistent Data Systems]
John R. Nestor. "IDL: The Language and Its
Implementation". Prentice Hall. Englewood Cliffs,