[web2py] web2py HL7: where come from "key:descriptions" of some tables?

[Pepe Araya]

Hello,

I'm trying to understand the Web2py HL7 App and I don't understand where 
come from the key:descriptions of some tables.

e.g:

"social_history" Table

id: 1
key: 229819007
description: Tobacco use and exposure (observable entity) Not available 
Smoking


is the key arbitrary or is a standard?

Thanks a lot.