Expert

9-26.

Which of the following statements accurately describe an object view and its capabilities?

  1. An object view is any SQL view found in the ALL_OBJECTS data dictionary view.

  2. An object view is a view that presents data stored in relational tables as an object.

  3. You can use an object view to navigate using REFs rather than joins.

  4. Object views can help you circumvent “schema evolution” problems that arise when working with the object layer of the Oracle RDBMS.

  5. If you decide to use object views, you can no longer make direct references to relational tables in your application.

9-27.

Object views allow us to layer an object-like approach onto existing (non-object) relational tables. Let’s apply object views to our compact disc example. Suppose that our compact_discs table is no longer an object table, but instead a relational table:


/* Filename on web page: objview.sql */
CREATE TABLE compact_discs (
   ID      INTEGER NOT NULL,
   title   VARCHAR2(60),
   artist  VARCHAR2(60),
   label   VARCHAR2(60),
   PRIMARY KEY (ID)
);

INSERT INTO compact_discs VALUES
   (100, 'White Album', 'Beatles', 'Apple');

We would then have a second table of keywords that are related to a compact_disc:

CREATE TABLE cd_keywords ( cd_id INTEGER NOT NULL REFERENCES compact_discs (id), keyword VARCHAR2(60) NOT NULL, PRIMARY KEY (cd_id, keyword) ); INSERT INTO cd_keywords VALUES (100, 'Lennon'); INSERT INTO cd_keywords VALUES (100, 'McCartney'); ...

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