Slide 16.28: Subtables

SQL3 (Cont.)

Value and Object Types
(Object-type example)

Methods observer and mutator are for querying and modifying an attribute value.
A constructor function serves to create or initialize values.

CREATE VALUE TYPE address
  street  VARCHAR(25),
  city    VARCHAR(25) );

CREATE OBJECT TYPE person (
  name     VARCHAR(30),
  age      INT,
  domicle  address );

CREATE OBJECT TYPE employee UNDER person (
  qualification  VARCHAR(30),
  salary         DECIMAL(7,2),
  familymembers  SET(person) );

CREATE TABLE company (
  name          VARCHAR(30),
  headoffice    address,
  subsidiaries  SET( VARCHAR(30) ),
  president     employee );

With the help of the options PUBLIC and PRIVATE it can be determined whether attributes and functions should be visible from the outside.

Subtables
Declare tables as subtables of already existing ones. Tables in SQL3 can be more than just sets of tuples. A table can be a

Set of tuples: Does not allow duplicate entries.
Multiset of tuples: Allows duplicate entries
List of tuples: Entries are stored in a specific sequence.

Every tuple within a table can be equipped with a unique row identifier.

(Row-identifier example)

CREATE TABLE person WITH IDENTITY (
  name      VARCHAR(30),
  age       INT,
  domicile  address,
  partner   person IDENTITY );