What is attribute?
         
            It is a properties of an entity type. Is entity with normally have one or more attribute. It may be thought of the smaller pieces of information with in an entity.

       Attribute may be categorised by-------
                a. Simple attribute
                b. Composite attribute
                c. Single valued attribute
                d. Multivalued attribute
                e. Derived attribute

a. Simple attribute:
                                     Attribute that could not be derived into subpart called simple attribute.                       

    For example, 'student_id','reg._no','employee_id' etc.

b.Composite attribute:
                                           Attribute that could be derived into subpart that are way of hierarchical organising attribute called composite attribute.

      For example, 'Name' is a composite attribute because it can be derived first-name, middle-name, last-name.

c. Single valued attribute:
                                                An attribute can take only one value for a given instance called single valued attribute.

      For example, 'roll-number' is a single valued attribute.

d. Multivalued attribute:
                                               An attribute may take more than one value of the given entity instance.

      For example,'phone_no' attribute for specific entity set may have more than one number.

e.  Derived attribute:
                                        An attribute whose value can be calculated from the related attribute values called derived attribute.

      For example, 'age' attribute can be derived from the date of birth attribute and so they are related.