UML Relationship between Customer and Product List (Java Supermaket Software)

I am trying to create a supermarket software that allows either a customer or the owner to log-in and use my system via a swing based GUI in Java. When the Customer has logged in they can view products. When the owner has logged in they can view products and add new products.

I want a method in the Customer class: ViewProducts()
and methods in the Owner class: ViewProducts(), AddProducts().
Are these methods wrong because they're not specific to the customer/owner (they're related to the product).

My relationship would be the Customer class having a 1 to 1 relationship with ProductList and the Owner having a 1 to 1 relationship with ProductList, and the two classes can manipulate the data in their own way. Am I going about this wrong?

This way doesn't make sense because Customer and Owner can't have attributes that aren't related to them such as ProductList.

You should always aim to capture what exists in reality. A Customer instance does not have a 1 to 1 relationship with a ProductList because a ProductList can be viewed by more than one Customer at a time, and the Customer in no way owns that list.

What is probably closer to reality is:

• Every Supermarket individual manages one Inventory individual
• Every Inventory individual:
  • is managed by one Supermarket individual
  • comprises Inventory Item individuals
• Every Inventory Item individual
  • is comprised by one Inventory individual
  • describes Product individuals
• Every Product individual
  • is described by one Inventory Item individual
  • is located at one Physical Location individual
• Every User Account individual
  • identifies one Person individual
  • plays Role individuals
• Every Role individual provides Capability individuals

In real life, people play roles. These roles might be “customer”, “doctor”, or “police officer”. Every individual Role has a set of capabilities it can perform. In an OO system, every individual Role can use operations to implement its capabilities, such as purchaseProduct(), prescribeMedication(), or writeMovingViolation().

There are multiple ways to represent these roles and capabilities in an OO system. In one approach, a customer instance of a Role might be configured to allow access to queryInventory() and purchaseProduct() operations on the Supermarket and InventoryItem classes respectively. An owner instance of a Role ¹ might be configured to allow access to addInventoryItem() and removeInventoryItem() operations on the Inventory class.

Here is an example of a UML model:

In another approach, you might create singleton subclasses of the Role class, called CustomerRole and OwnerRole, and then have each of those subclasses invoke operations. You might put your viewProducts() and addProducts() operations into those singletons.

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¹ Consider calling this role “manager”, so the owner of the supermarket can hire other people to do the work.