Buy a Product conceptual model

A conceptual model (domain model) shows the concepts of the real domain, their attributes and associations. It is not a software design. Candidate concepts are found by identifying the nouns in the scenario.

Concepts: Customer, Catalog, Item (product), ShoppingBasket, BasketLine (basket item), Sale (order), CreditCard, ShippingInfo, CreditCardAuthorization (payment authorization), EmailConfirmation (follow-up e-mail).

Assumptions: one basket per customer visit; a sale is made from the basket when the customer pays; one authorization per sale.

                          lists
 +---------+ 1                  * +--------+
 | Catalog |----------------------|  Item  |
 +---------+                      +--------+
                                       | 1
                                       | refers to
                                       | *
 +----------+ 1  0..1 +----------+ 1  1..* +------------+
 | Customer |---------| Shopping |---------| BasketLine |
 +----------+   has   | Basket   | contains| (quantity) |
      | 1             +----------+         +------------+
      | places             | 1
      | *                  | becomes
 +----------+ 0..1         |
 |   Sale   |--------------+
 +----------+
  |    |    |    |
  |    |    |    +-- confirmed by --> EmailConfirmation (1)
  |    |    +------- authorised by --> Authorization (1)
  |    +------------ paid with ------> CreditCard (1)
  +----------------- shipped to -----> ShippingInfo (1)

The main associations with multiplicity:

Attributes (examples): Customer(name, email, address); Item(id, name, price); BasketLine(quantity); CreditCard(number, expiry, holderName); ShippingInfo(address, method); Sale(date, total, status); Authorization(code, status, date).