Question about extending schemas at run-time


I posted this in the Ruby forum - but someone suggest that I should try
posting in the Rails as I’ll be using Rails: (sorry for the repost)

I’m sure this has been brought up before but I probably am using the
wrong keywords to search. I’d like to know if there is a way to use Ruby
to create dynamic schemas. As an example, I’d like to create an
administrative page that would allow administers to add or remove fields
from that page - which results in a modification to the schema of the
table in the database. Can this be done at runtime without having to
restart Ruby?