In Object (and Class) Orientation, everything is consider an object, even non objects !!!
Modules, namespaces, and libraries, are one of the things that U.M.L. creators seems to overlook.
Many designers represent global elements, enclosed in a file, namespace or module, representing the module as a single object or class.
I languages like Javascript, modules, are enclosed by a singleton object or global object.
This is a generic example of how non O.O. may be implemented.
......................................................................
..+----------------------------------------------------------------+..
..| <<module>> |..
..| Strings |..
..+----------------------------------------------------------------+..
..| [+] String[]: Letters <<constant>> <<global>> |..
..| [+] String[]: Digits <<constant>> <<global>> |..
..+----------------------------------------------------------------+..
..| [+] String: ToUppercase(String Value) <<function>> <<global>> |..
..| [+] String: ToLowercase(String Value) <<function>> <<global>> |..
..+----------------------------------------------------------------+..
......................................................................
Cheers.