I am designing a database of shareholders for a small corporation. I was all set with three basic tables: Certificates, Shareholders, and Transaction_Details. Then I started data entry. An assumption I made in my design was that each certificate would have only one shareholder associated with it. (That is the corporation's current practice.) But as I started entering historical data, I came to a certificate that had multiple shareholders! This can't be "fixed". It happened and everyone involved is long dead. I have to account for it.
I'm having trouble coming up with HOW. Each Shareholder has an ID number and each certificate has a number. How do I relate things such that multiple shareholders can be represented as owning a single certificate?
Examples I find online involve the classic Products/Customers/Orders many-to-many design. But they all assume that each order is made by only one customer.