Answer to Question 1
Generalization is a relationship in which one class is the more abstract expression of the properties of a set of classes: a Tree class embodies properties common to Oak, Birch, and Cedar classes. Conversely, specialization is a relationship in which a class is the less abstract expression of another class: a Rose is a Flower but the Flower class does not express the specific features of a Rose that sets it apart from other flowers. The result of generalization is a superclass (or a parent), while specialization arrives as subclasses (or children).
Answer to Question 2
A relational DBMS protects data integrity at four levels: column (or attribute), row (or entity), inter-table, and procedural.
Attribute integrity is ensured by type definition, foreign keys, and constraints.
Entity integrity is assured by the primary key: one, and only one, entity within a table can be identified by a specific value (or combination of values) in the primary key.
Inter-table integrity is called referential integrity and is implemented by enforcing the constraints of foreign keys.
Procedural integrity is used when the relationships among entities are too complex for the other mechanisms. The main tools of procedural integrity are triggers, stored procedures, and transaction processing.
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