Best way to set global vars/constants?

[eluser]Medikal[/eluser]
Hey guys, just curious. I have a ton of things I would like to set to global constants I can use anywhere just for ease of the use in the future in case I change anything. My best example is I'm constantly using $this->db->from("articles") or something of the sort, I'd rather have a constant defined as ARTICLES_TABLE and always refer to it as that so if the table name changed I could change it in one file for every query, among other things.

Cheers.