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No, we do not have that. The table names and their field names are very much self-explanatory and follow Joomla's conventions.

Also note that there are no foreign in our tables or Joomla's tables. That's a deliberate choice Joomla has made. Handling relations in software instead of the database layer itself allows it to fire plugin events when a database record is created, updated, or deleted. This is what makes it such a powerful CMS and allows for features like custom fields and tags (which are handled by Joomla itself; we don't interface with these database tables directly in our code!). 

Also note that since Joomla and ATS are compatible with both MySQL and PostgreSQL, and the fact that these two RDBMS don't have 1:1 mapping of field types, the schemas are functionally equivalent but not identical. A diagram would always be diverging from the schema unless we kept separate diagrams for each RDBMS, quadrupling the work we have to do for every schema change. That's a lot of error-prone work without any benefits for us, only downsides.