Modeling Subclass (or Subtype) Constraints in an Entity-Relationship Diagram

Scenario description

Can someone help me out on how to model the situation that follows:

-
There is a superclass (or supertype) called PRODUCTS, which has the subclasses (or subtypes) named FOOD and SHOES.

-
There exists another superclass denominated CUSTOMERS, with the subclasses denominated SHOE STORE and GROCERY STORE.

-
I need to represent some rules that indicate that:

• FOOD can only be delivered to GROCERY STORES.

• SHOES can exclusively be distributed to SHOE STORES.

Tentative diagrams

I have tried the two diagrams shown bellow:

Diagrams considerations

Top diagram

I really do not like the duplication of (a) the same entity type, i.e., ORDERS, and (b) the relationships around it.

Bottom diagram

I am pretty sure this not the proper notation. Should I instead create the relationship on the superclass level and make a note that the restrictions will be implemented at the programming level?

I think you can make an Orders entity that is a relationship between Products and Customers. The Orders would have subclasses FoodOrders and ShoeOrders, which respectively would be the relationships between the subclasses of Food - GroceryStores and Shoes - ShoeStores.

┌───────────┐
│ Employees │
└─────┬─────┘
│
│
┌──────────┐ ┌────────┐ │ ┌───────────┐
│ Products ├─── contain ───┤ Orders ├─── deliver ───┤ Customers │
└────┬─────┘ └────┬───┘ └─────┬─────┘
│ │ │
│ │ │
isA isA isA
│ │ │ │ │ │
┌────┘ └────┐ ┌─────┘ └─────┐ ┌────┘ └────┐
│ │ │ │ │ │
┌───┴──┐ ┌───┴───┐ │ │ ┌───────┴───────┐ │
│ Food │ │ Shoes │ │ │ │ GroceryStores │ │
└───┬──┘ └───┬───┘ │ │ └───────┬───────┘ │
│ │ ┌─────┴──────┐ │ │ ┌─────┴──────┐
└───────────│───────┤ FoodOrders ├──────│────────────┘ │ ShoeStores │
│ └────────────┘ │ └─────┬──────┘
│ ┌─────┴──────┐ │
└─────────────────────┤ ShoeOrders ├─────────────────┘
└────────────┘


StackExchange Database Administrators Q#126952, answer score: 6