The most detailed, comprehensive and up to date diagram is here
That is forMoodle 3.4 and I intend to create diagrams for 3.5 and 3.6 when 3.6 becomes available. Note that in addition to the main diagram there are diagrams for the sub-systems.
The 3.4 diagram is now here:
http://www.examulator.com/er/3.4/index.html
The above link goes, as of Nov 18/2018 to version 3.5.
Thanks to Marcus for making these available!
Gerald