Visibility

Visibility applies to attributes or operations, and specifies the extent to which other classes can use a given class's attributes or operations.

Three levels of visibility are possible (last symbols are used in UML classes to indicate different levels of visibility):
	public level	usability extends to other classes	+
	protected level	usability is open only to classes that inherit from original class	#
	private level	only the original class can use the attribute or operation	-

Public and private operations in a HardDisk