subtype 1.inherits all attributes of the supertype 2.inherits all relationships of the supertype 3. usually has its own attributes or relationships 4. is drawn within the supertype 5.never exists alone 6.may have subtypes of its own 7.is also known as "subentity" EXAM is a supertype of QUIZ, MIDTERM, and FINAL. The subtypes have several attributes in common. These common attributes are listed at the supertype level. The same applies to relationships. Subtypes inherit all attributes and relationships of the supertype entity. the two subtype rules: 1.Exhaustive: Every instance of the supertype is also an instance of one of the subtypes. 2. Mutually Exclusive: Every instance of the supertype is of one and only one subtype. Barred Relationships The unique identifier (UID) of the intersection entity often comes from the originating relationships and is represented by the bars. In this case, the relationships from the originating entities to the intersection entity are called "barred" relationships. GOOD LUCK SEE YOU NEXT MEETING Raafat Rashad
