[TYPO3-mvc] How to extend existing tables with ExtBase?

[David Schreiber]

Hello,

After some tryouts with my first ExtBase extension, I came to the 
conclusion it would be best to extend an already existing TYPO3 table 
(namely fe_users).

Like I thought, now I get following error message when accessing my 
plugin in the frontend:

"Table 'rrmarket_01.tx_mmfrrmarket_domain_model_member' doesn't exist"

This is because my model is called Member, but the table which should be 
used is fe_users. Is it possible to use existing tables with ExtBase so 
that I can easily extend fe_users, or do I need to create a separate 
table and do some kind of complicated "linking" between my table and the 
fe_users?

Thank you very much,
David Schreiber