While doing some diagrams, and checking out tools to do so, I am reminded of a saying attributed to Andrew S. Tanenbaum "The nice thing about standards is that there are so many to choose from".

Really, there are some diagramming standards I now encounter that I have never even remotely heard of before, and probably rightly so. A small selection, to date:

• EXPRESS, a visual data-modeling language used for product descriptions
• Nass-Shneiderman-Diagrams, which appear to be some reformulation of flow-charts without arrows. Apparently popular in high school teaching or something.
• Bond graphs, used for physical dynamical systems and if the Wikipedia examples are anything to go by, they can be drawn in ASCII!
• Some kind of microelectronic circuit schema that I could not find a reference for, but which has a METAPOST module (btw, all of the above have, just google for their name and metapost).

Besides that, I now consider it established beyond doubt that there are so many variations of "block diagram" that the term has ceased to be of any discriminatory power whatsoever.