I haven't come across this issue before and can't find it in my Schaum's Outline UML book and was wondering if someone here could help. I'm making a use case diagram for e-commerce, and in it I want to describe that in order to add a book to your shopping basket, you have to either search products (using the websites search engine) or browse products (using navigation). But the thing is that it can be either one, and not both. Is there a way to show that adding a product to the basket needs to include either this or that? Because otherwise it would look like it needs to include both. Or should I join the two use cases (search products and browse products) into one?