when OO-designing...

I'm new to OO- design.
I've had some Relational experience.
I'm confused.

For example, when I design classes which one is the better?

I have three classes called, CUSTOMER,ORDER,PRODUCT.
CUSTOMER have three attributes, customer_ID, customer_name, customer_address.
PRODUCT have three attributes, product_ID, Product_name, Product_price

First option of ORDER is
class ORDER {
   string order_code;
   string product_id;
   string customer_id;

The other is as follows.
class ORDER {
   string order_code;
   Product _product;
   Customer _customer;

In relational database design, when you design n:n relationship of two entities the relational entity comes around like,

when customer orders products customer,

cardinality n:n
intermediate table(order) comes out.
so we can use the PK of two tables(product,customer) as FK of the ORDER table.

Are there criteria like above in OOAD?

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OviConnect With a Mentor Commented:
From the OOP design point of view, modeling a such "system" is like in real world. Of course you can model in any way you want, but the essance of OOP is modeling real live objects to programming models. So in my opinion if you analyze the sentence : Customers order Products, you have two fine defined and stable entities : Customer and Product. Ordering is an action which links those two entities one to another. Now this order action can be broken in many types of ordering. The base structure of an order is a customer id and productS idS (a customer can order at least one product). So the design of Order class should by in my oppinion :
class Order {
  private String orderId;
  private String customerId;
  private String[] productIds; //or Vector of product idS

If you want to implement in future different kind of orders I suggest to create the above class as abstract, and use different order types as derivate classes of this one. In this way you will respect most of the OOAD principles.

If you are realy interested into some OOAD principles you should follow this link :

www.objectmentor.com/resources/articleIndex section "Design Principles"
Well.. ya only need to learn Associattion and bit about Composition or say containment theory n you will be able to solve your problem.. i couldn't suggesti ne thing.. cuz this is the basic problem when one comes from a  relational background to OOP .. its better to learn about what i mentioned above.. n you would be having a fair idea of such Entity Relations.. in OOD.. by they way these are kinda basics so ya must go through to these topics
iamjhkangAuthor Commented:
Yes. It's basics.
I know relationships between classes, association and composition.
You know basics, I want experts's comments on the basics.
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iamjhkangAuthor Commented:
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