zrail, it's difficult to find the schema and/or tables in the source code as all of them are 100% dynamic. See my coments above about the internal workings of ToroDB. Or give it a try, run it and check how data is laid out!

Regarding the use of cursors, they are absolutely necessary, as there is -in MongoDB- the concept of a session, and queries may be asked in subsequent packets to return the next results. However, I don't see how this impedes to take advantages of the relational model. ToroDB definitely does that, if you look at the created tables schema.