Specifically for ZABBIX 4.0, is the Entity Relationship Diagram (ERD) or Database Schema available from anybody? Thanks!
The documentation is quite outdated, the schema is for the 2.4 version.
However you can use MySQL Workbench to plot it: connect to Zabbix's mysql, then Database -> Reverse Engineer and follow the steps.
Here's a sample from my Zabbix 4.0 server: