-1NF, 2NF, and 3NF are normalization stages
-A specialization hierarchy can have many level(s) of supertype/subtype relationships.
-An entity supertype is a generic entity type that is related to one or more entity subtypes.
-At the implementation level,
1.Advantages of Entity Relationship Model: -Requires substantial
hardware and system software overhead
-Conceptual simplicity gives untrained people the tools to use a good
-May promote information problems
2.Advantages of Hierarchical Model