What is object relational model? Discuss object relational features of SQL.

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 The relational model with object database enhancements is sometimes referred to as the object-relational model. The following are some of the object database features that have been included in SQL:

  • Some type of constructors has been added to specify complex objects. These include the row type, which corresponds to the tuple (or struct) constructor. An array type for specifying collections is also provided. Other collection type constructors, such as set, list, and bag constructors, were not part of the original SQL/Object specifications in SQL: 99 but were later included in the standard in SQL: 2008.
  • A mechanism for specifying object identity through the use of reference type is included.
  • Encapsulation of operations is provided through the mechanism of user-defined types (UDTs) that may include operations as part of their declaration. These are somewhat similar to the concept of abstract data types that were developed in programming languages. In addition, the concept of user-defined routines (UDRs) allows the definition of general methods (operations).
  • Inheritance mechanisms are provided using the keyword UNDER.


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