Imagine I have a content type that has two fields of type category: one is a taxonomy Author and another one is a taxonomy Topics, these two taxonomies are unrelated, the only 'thing' they may have in common is the component itself.
Now we go to the website as a visitor, then when the visitor clicks on a given Author I want to create a list with all the Topics that are present in Components that also contain the specific Author.
I know I could create a query object with a criteria containing both keywords from the different taxonomies to check if it retrieves any values, the problem is that I would need to do that for every single topic i.e. Author and Topic1, Author and Topic2, Author and Topic 3 etc, in the end it may mean tens of queries which I obviously don't want to do.
As I see it the taxonomy API won't help because both taxonomies and thefore their keywords are completely unrelated. Any alternatives?