Is there a way to see the Eloqua Database Schema without using a BI tool?

Specifically, I'd like to understand how the campaign activity object is related to to the email activity object in Insight. I do not have access to a BI tool to understand the relationship/key field between the tables/objects, so I cannot see a schema to determine this. Although, it would be nice to understand how all these tables/objects are connected. Apart from using a tool, are there any documented resources to reference this?