Was sind und was sollen ... relational arrows?

Was sind und was sollen ... relational arrows?

I can remember asking myself this question sometime in the early 1980's.
I worked on it a little more in the middle of that decade, as I was
passing through Champaign-Urbana, taking a course from John Gray
on "Applications of Lambda Calculus", and thinking a lot about
the mutual applications of category theory and computer science
to each other.  I appear to be doomed to return to the question
from time to time, at least for the time being.

I started recording a few notes of what I can recall of my own approach
at the n-Lab wiki, so maybe that will serve as sufficient primer to get
the ball rolling:

* http://ncatlab.org/nlab/revision/relation+theory+%3E+history/35

* http://mathoverflow.net/questions/6590/was-sind-und-was-sollen-relational-arrows