I agree that the curent object types in Oracle aren’t practical for transient objects, first because we need references between transient objects.
But, I think that Oracle object types are OK for persistent objects – for “column objects”, not for “row objects”:
“OR(DBMS) or R(DBMS), That is the Question”
http://www.quest-pipelines.com/pipelines/plsql/tips.htm#OCTOBER

C.J.Date in “An introduction to Database Systems” (2004, page 885) says:
“… object/relational systems … are, or should be, basically just relational systems that support the relational domain concept (i.e., types) properly
- in other words, true relational systems, meaning in particular systems that allow users to define their own types.”

Best regards,
Zlatko

My opinion is that PL/SQL classes (object types) still aren’t finished.
Database 9i has made a giant leap forward compared to 8i (inheritance, polymorphism …),
but in 10g there is hardly anything new.
In my opinion it is a priority to add references between transient objects and then,
perhaps, even a garbage collector.

Between the way, I sent my PL/SQL “wish list” to Steven Feuerstein’s site “21st Century PL/SQL”
http://www.oracleplsqlprogramming.com/IC/ideas/data_structures_and_datatypes/object_types/index.php
(Add advanced O-O features like those found in Eiffel)
and
to the AskTom site: Thanks for the question regarding “What don’t you like about Oracle?”
http://asktom.oracle.com/pls/ask/f?p=4950:8:4407442689342146348::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:48704116042682
(My wishes – new features of Oracle Database 11br).

In addition, I present you my two texts in witch I’m pointing out some of PL/SQL object oriented characteristics:
Calling the Parent Object’s Version of an Overridden Method
http://www.quest-pipelines.com/pipelines/plsql/tips03.htm#JUNE
and
Dynamic Method Dispatch and Method Overloading in a Subtype
http://www.quest-pipelines.com/newsletter-v4/0503_C.htm

But, adding more OO capabilities to PL/SQL is the second thing in my wish list.
The first thing is – better support for business rules in the database.
We need “What Not How: The Business Rules Approach to Application Development” (book by C.J.Date).
My motto is: “Thou shall not do in the Middle Tier, what thou could have done in the Data Tier”
(Toon Koppelaars in “A first JDeveloper project: Choices made, lessons learned”, Oracle World 2002).

If the database would support business rules, then this two complex examples would be futile:
Solving “COMMIT business rules” on the Database Server
http://www.oracle.com/technology/oramag/code/tips2002/032402.html
and
Avoid a “Vicious Cycle”
http://www.oracle.com/technology/oramag/code/tips2003/081003.html

Best regards,

Zlatko Sirotic

Thanks a lot for this very interesting example! Most of us tend to shy away from using the Oracle Object Extensions – certainly in part because of ignorance – so having your demonstration is valuable to a lot of us, including myself.

Are you making use of the Object Extensions and the OO facilities available for Object Types a great deal?

best regards,

Lucas

But then in PL/SQL 9i/10g we must use MEMBER (non-STATIC) methods (procedures/functions):

CREATE OR REPLACE TYPE templ_method_abstract AS OBJECT (
dummy VARCHAR2(10),
MEMBER PROCEDURE template_method,
NOT INSTANTIABLE MEMBER PROCEDURE operation1,
NOT INSTANTIABLE MEMBER PROCEDURE operation2
)
NOT FINAL
NOT INSTANTIABLE
/
CREATE OR REPLACE TYPE BODY templ_method_abstract IS
MEMBER PROCEDURE template_method IS
BEGIN
operation1;
operation2;
END;
END;
/

CREATE OR REPLACE TYPE templ_method_concrete_a UNDER templ_method_abstract (
OVERRIDING MEMBER PROCEDURE operation1,
OVERRIDING MEMBER PROCEDURE operation2
)
/
CREATE OR REPLACE TYPE BODY templ_method_concrete_a IS
OVERRIDING MEMBER PROCEDURE operation1 IS
BEGIN
DBMS_OUTPUT.PUT_LINE (‘Operation 1 in class CONCRETE A’);
END;

OVERRIDING MEMBER PROCEDURE operation2 IS
BEGIN
DBMS_OUTPUT.PUT_LINE (‘Operation 2 in class CONCRETE A’);
END;
END;
/

CREATE OR REPLACE TYPE templ_method_concrete_b UNDER templ_method_abstract (
OVERRIDING MEMBER PROCEDURE operation1,
OVERRIDING MEMBER PROCEDURE operation2
)
/
CREATE OR REPLACE TYPE BODY templ_method_concrete_b IS
OVERRIDING MEMBER PROCEDURE operation1 IS
BEGIN
DBMS_OUTPUT.PUT_LINE (‘Operation 1 in class CONCRETE B’);
END;

OVERRIDING MEMBER PROCEDURE operation2 IS
BEGIN
DBMS_OUTPUT.PUT_LINE (‘Operation 2 in class CONCRETE B’);
END;
END;
/

DECLARE
l_templ_method_object templ_method_abstract;
BEGIN
l_templ_method_object := NEW templ_method_concrete_a (‘DUMMY’);
l_templ_method_object.template_method;

l_templ_method_object := NEW templ_method_concrete_b (‘DUMMY’);
l_templ_method_object.template_method;
END;
/

Why we can’t use STATIC methods?
First, in PL/SQL 9i/10g STATIC method can’t bee abstract (NOT INSTANTIABLE):

CREATE OR REPLACE TYPE template_method_abstract_2 AS OBJECT (
dummy NUMBER(1),
STATIC PROCEDURE template_method,
NOT INSTANTIABLE STATIC PROCEDURE operation1,
NOT INSTANTIABLE STATIC PROCEDURE operation2
)
NOT FINAL
NOT INSTANTIABLE
/

LINE/COL ERROR
——– —————————————————————–
4/38 PLS-00169: modifier ‘STATIC’ conflicts with prior ‘NOT
INSTANTIABLE’ specification

5/38 PLS-00169: modifier ‘STATIC’ conflicts with prior ‘NOT
INSTANTIABLE’ specification

Second, we can try to use non-abstract STATIC methods in (abstract) parent:

CREATE OR REPLACE TYPE template_method_abstract_3 AS OBJECT (
dummy NUMBER(1),
STATIC PROCEDURE template_method,
STATIC PROCEDURE operation1,
STATIC PROCEDURE operation2
)
NOT FINAL
NOT INSTANTIABLE
/
CREATE OR REPLACE TYPE BODY template_method_abstract_3 IS
STATIC PROCEDURE template_method IS
BEGIN
operation1;
operation2;
END;

STATIC PROCEDURE operation1 IS
BEGIN
NULL; — simulates abstract method
END;

STATIC PROCEDURE operation2 IS
BEGIN
NULL; — simulates abstract method
END;
END;
/

but, (in PL/SQL 9i/10g) we can’t override STATIC method:

CREATE OR REPLACE TYPE template_method_concrete_3 UNDER template_method_abstract_3 (
OVERRIDING STATIC PROCEDURE operation1,
OVERRIDING STATIC PROCEDURE operation2
)
/
LINE/COL ERROR
——– —————————————————————–
2/32 PLS-00169: modifier ‘STATIC’ conflicts with prior ‘OVERRIDING’
specification

3/32 PLS-00169: modifier ‘STATIC’ conflicts with prior ‘OVERRIDING’
specification

Regards,
Zlatko Sirotic

I think it worth to show those design patterns also using oracle types