How to name the class of the element of the library (the one where books and magazines)?

Question

Programming

I am developing a project in Ruby.
It will be an open natural science electronic library.
Books, periodicals, Internet publications, articles will be placed there.
There was a common situation for a programmer, what name to give a variable (in this case, a class)?
Throw in the name of a common class for the elements of the library (it can be a book or an article, etc.), preferably in one word.
At first I thought to call simply Item, but later I considered it a little informative name and commonly used in other parts of the code, the same with Element.

Answer 1

Maybe Card?
Like cards that are assigned to books, magazines in a real library.
Or title.

Answer 2

publication, for example

Answer 3

Paper, Publication