Single valued and multi valued attributes

Single Valued attribute: 

Attributes that can have single value at a particular instance of time are called single valued. A person can’t have more than one age value. Therefore, age of a person is a single-values attribute.

Multi valued attributes: 

A multi-valued attribute can have more than one value at one time. For example, degree of a person is a multi-valued attribute since a person can have more than one degree. Where appropriate, upper and lower bounds may be placed on the number of values in a multi-valued attribute For example, a bank may limit the number of addresses recorded for a single customer to two. Such attributes are represented by double ovals in ER diagram.