EDIT: I guess I wasn't as clear with this question as I had intended. I know how to search for multiple keywords, what I don't know how to do is assign multiple keywords to the same item:
I am making a database of journal articles, with the intent that people can search through it via keywords. While it is fairly easy to let people search for multiple keywords (gathering all articles that have this term AND that term) I have not found/seen a way to assign multiple keywords per article. As a simple example:
item 1 is "shiny"
item 2 is "blue"
item 3 is "shiny" AND "blue"
item 4 is "round" AND "shiny"
I would like the user to be able to search for "shiny" and have items 1,3,4 come up or search for "blue" and have items 2,3 come up etc.
@David W. Fenton mentions a "N:N join table". I have no idea what that is but he describe exactly what I want to do: "Storing multiple attributes in a single field" as if it is impossible, I would have thought that would be a not uncommon usage.