Who uses inheritance?
I had a conversation with Tom Kyte on PL/SQL and OO (see thread http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:63942113457534#642059000346437745 ).
When I program in C#, I use a lot of inheritance and polymorphism, why not in PL/SQL?
Do you readers have good examples that show how you can use inheritance and polymorphism?
I hope that there will come support for encapsulation in Oracle Objects.
I like both, I like PL/SQL and I like C# (very OO).Like you, I like PL/SQL and I like OOPL's.
I don't know C# - I know C++, Java and Eiffel, but I'm not an expert.
In my opinion, Eiffel is the best OOPL (Eiffel was designed in 1985, commercialy released in 1986, ISO-standardized in 2006).
But mostly I like relational databases (relational DBMS's).
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).
I think that the current object types in Oracle aren't practical for transient objects in PL/SQL,
first because a "true" OOPL must have 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"
(Add advanced O-O features like those found in Eiffel)
http://www.oracleplsqlprogramming.com/IC/ideas/data_structures_and_datatypes/object_types/index.php
Here are my attempts to use PL/SQL as OOPL ( PL/SQL++ :) :
Dynamic Method Dispatch and Method Overloading in a Subtype (May 2003)
http://www.quest-pipelines.com/newsletter-v4/0503_C.htm
Calling the Parent Object's Version of an Overridden Method
http://www.quest-pipelines.com/pipelines/plsql/tips03.htm#JUNE
(note: Oracle 11g has Generalized Invocation)
How to Get the Text Name of an Object's Type
http://www.quest-pipelines.com/pipelines/plsql/tips06.htm#JULY
The Template Design Pattern in PL/SQL
http://www.quest-pipelines.com/pipelines/plsql/tips06.htm#OCTOBER
Design by Contract (DBC) and PL/SQL
http://www.quest-pipelines.com/pipelines/plsql/tips.htm#JUNE
But, I think that Oracle object types are OK for persistent objects (for “column objects”, not for “row objects”).
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".
Here is an attempt to use Oracle "object-relational" features "in the proper way" (in Date's sense) - to use object type as domain:
“OR(DBMS) or R(DBMS), That is the Question”
http://www.quest-pipelines.com/pipelines/plsql/tips.htm#OCTOBER
Regards,
Zlatko
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java support both inheratiance and composition .I also know "is a" and
"has a realitionship" but there is always a problem with me to understanding whethere i have to use extends or having a object of a class has a member of othere class.
and also "A pure OOP must support polimorphisim,inheretiance,encapluction,Abstraction and Composition" correct me if i am wrong
thank you and have a nice day.Bruce Eckel, author of Thinking In Java, has this to say about composition vs. inheritance:
When deciding between inheritance and composition, ask if you need to upcast to the base type. If not, prefer composition (member objects) to inheritance. This can eliminate the perceived need for multiple base types. If you inherit, users will think they are supposed to upcast.
Choose composition first when creating new classes from existing classes. You should only used inheritance if it is required by your design. If you use inheritance where composition will work, your designs will become needlessly complicated.
Bill Venners: Composition versus Inheritance
Use inheritance (of implementation) only when the class satisfies the following criteria:
1) "Is a special kind of," not "is a role played by a";
2) Never needs to transmute to be an object in some other class;
3) Extends rather than overrides or nullifies superclass;
4) Does not subclass what is merely a utility class (useful functionality you'd like to reuse); and
5) Within PD: expresses special kinds of roles, transactions, or things.
-- from Java Design: Building Better Apps and Applets (2nd Edition), by Peter Coad and Mark Mayfield
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