panda17

Regarding the "industry term", search:

   site:oracle.com "alternate key"

   site:microsoft.com "alternate key"

   site:ibm.com "alternate key"

In general there can be more than one candidate key for a given relation (table). Only one candidate key is "primary", all others are "alternate".

A thing is uniquely identified by T, category by C.

May read it as: CREATE TABLE thing (T_ID integer, C_ID integer)

Sorry, firewall thing -- dependent on recent (geo-ip) threats. Nothing to do with ads -- no ads.

Consider starting with these two papers, and then ...

Michael Stonebraker et al., Architecture of a Database System, 2007.

Michael Stonebraker et al., The End of an Architectural Era, 2007.