Reference Types

Object-oriented language provides the ability to refer to objects. An attribute of a type can be a reference to an 0bject of a specified type.

In order to initialise a reference attribute, one need to get the identifier of the tuple that is to be referenced. One can get the identifier value of a tuple by means of a query. Thus, to create a tuple with the reference value, one may first create the tuple with a null reference and then set the reference separately.

one where the referenced table must have an attribute that stores the identifier of the tuple. One declares this attribute, called the self-referential attribute by adding a ref is clause to the create table statement.