In relation algebra, the symbol is

	a.	Union
	b.	Set different
	c.	Set intersection

A recursive (role) relationship is a relationship between an entity and ________.

	a.	subtype entity
	b.	itself
	c.	an archetype entity

And (), or (v) and not ( ) are called

	1.	set of attributes
	2.	set of comparison operators
	3.	set of connectives
	4.	set of constants

Having the same number of attributes is called

	1.	unity
	2.	identity
	3.	compatibility
	4.	same arity

.. ensures that the database remains in a correct state despite system failures and transaction failures

	a.	Transaction manager
	b.	Transection
	c.	Transection-managment component
	d.	Concurrency-control manager