Constructor methods initialize a structured UDT instance with input arguments, creating an instance value for the type. The ANSI SQL standard defines something called a site, which is little more than an umbrella name assigned to a large set of different kinds of variables. Incorporating this definition, a structured UDT is seen to determine a type that is the data type of a site. Again, this does little more than state that a structured UDT is the data type of an instance of a variable.
A constructor method, then, assigns specific values to the elements of a site according to the attributes of the structured UDT that is the data type for that site.
The specification of a constructor method must comply with the following rules: