1NF vis-a-vis Business Rules

A practical way to think of 1NF in the above table is to ask a series of questions about the relationships that records (rows) can have between entities (tables) or attributes (columns), based on given business rules or constraints. For example, could a Subscriber record relate to many Email Address records? Could an Email Address record relate to many Subscriber records?

 http://en.wikipedia.org/wiki/First_normal_form