There are various restrictions on the data that can be stored in a relational database. These are called constraints . The constraints are domain constraints, key constraints, entity integrity constraints, and referential integrity constraints. These constraints ensure that there are no ambiguous tuples in the database. SQL includes statements for data definition, modification, querying and constraint specification.
All processing is based on values in fields of records.
The SQL standard enables users to easily migrate their database applications between database systems. The main features of OO programming languages are encapsulation, inheritance and polymorphism. Encapsulation can be thought of as a protective layer that prevents the code and the data from being accessed by other code defined outside the layer. The process in which one object inherits the properties of a previously defined object is called inheritance . Inheritance aids in the reuse of existing definitions for creating new objects.