About Version Vectors (a.k.a. Vector Clocks) by Kresten Krab Thorup.
Using spreadsheets as an example, Kresten explains how version vectors can solve a large class of versioning issues but not all.
Assuming you are interested in distributed topic map systems, versioning that leads to acceptable (not perfect) results will interest to you.
This is going to become more important as topic maps develop into distributed systems.