Slide 16.13: Generating and modifying objects

Desired Properties (Cont.)

Implications of a Class Hierarchy (Cont.)

Objects of a heterogeneous set are to be represented only by their identities.

Disadvantage: Needs further processing.

For example, determines both employees and other persons over 50 and then process the data depending on their class membership.
CASE ( SELECT * FROM person WHERE age > 50 ) IF employee THEN ... ELSE ... END CASE;

Generating and Modifying Objects

To generate new objects of a certain class, assume the existence of a generic method “new” which could be applied to every class. Inserting new objects into the class address could be implemented as follows:
INSERT NEW( street, location ) VALUES( 'Broadway', 'New York' ) INTO address;

The modification operation ensures that Ford will manufacture only red cars.
UPDATE vehicle SET color = 'red' WHERE manufacturer.name = 'Ford';

Insert a new vehicle for which an object manufacturer already exists.
1. Select the identity of the manufacturer with the name of Ford in the variable m.
  m := SELECT f FROM f IN company WHERE name = 'Ford';