I have two forms, Company and Client. A company can have any number of clients, and a client can be a client of any number of companies. I want to be able to do things like list a given company's clients, or list the companies that a given client employs. What is the best way to deal with this using the Domino database structure?
That's no problem.
Create categorized views for companies and for clients. Then, store the company names on each client document and client names on each company document. Use a single-category embedded view to list them on each form. Clicking on the name in the embedded view opens the document.
Or, create a third form type for company-client relationships and use that to populate the embedded view.