IDEF’s approach to Object-Oriented Design.
IDEF4 is a method for approaching Object-Oriented Design that was introduced alongside the other IDEF methods (IDEF). It’s not widely in use in its base form, but serves as a predecessor for things like UML. It contains many diagrams and datasheets.
Notably many of the diagrams logically contained under ‘Class Submodel’ are very similar to Class Diagrams. It also includes things like these:
And also State Diagrams, like so:
Interestingly, Entity-Relationship Diagrams in IDEF4 use a Crow’s Notation, rather than the notation specified in IDEF1X.
I don’t intend to ever learn much more about this method. I’ve scrolled through the IDEF4 spec. Good ‘nuff.