Problem with EER Diagram

[Jeroen Steenhuis]

Hello,

I want to create a database with customers, projects, products and suppliers.

In this case a customer had the same address information as a supplier and thus is a contact.

So I created a table contact, a table project and a table product.

Then I get the next relations:

A customer (is a contact) owns zero or many projects, so they have a relation.
A project has zero or many products, so they have a relation.
A product has one supplier (is a contact) so they also have a relation.

The problem in this case is that there is kind a circular reference.

When I create this with MySQL workbench it will create all relations correct but not the relation between a product and its supplier (contact). It will then connect back to the project and create a new extra relation to contact.

A possible solution is to use separate tables for both customer and supplier, but this can create double data, because a customer can also be a supplier.

How do I solve this problem?