Recently we had a customer get an exception when trying to manage a user group with a name longer than 16 characters:

opennms=# \d category_group;
Table "public.category_group"
Column | Type | Modifiers
---------------------------------------------- categoryid | integer | not null
groupid | character varying(16) | not null

I think 16 is a little small - we should go with at least 32 or 64. Also, it would be nice to check for this in the webUI to prevent an exception.