Parameter and Keyword Description:

record_type_name:

This identifies the user-defined type specifier that is used in the subsequent declarations of the records.

NOT NULL:

This constraint prevents the assigning of the nulls to the field. At the run time, trying to assign the null to a field, defined as NOT NULL raises the predefined exception VALUE_ ERROR. The constraint NOT NULL should be followed by an initialization clause.

datatype:

The datatype is a type specifier. 

:= | DEFAULT:

This keyword or operator allows you to initialize the fields to the default values.

expression:

This is a indiscriminately complex combination of the constants, variables, literals, operators, & function calls. The easiest expression consists of a single variable. When the declaration is explained, the value of the expression is assigned to the field. The value and the field should have the compatible datatypes.