Views is a great tool to create complex SQL queries and display their results on your Drupal site even if you don't know what this actually means. It's great. This session though is aimed at people who do know and might be confronted with tasks like that:

We want a summary of how many users have been accepted or refused a certain role. There's a view and we want you to display a block that shows this numbers in the sidebar. By the way if our users only want to see people from a specific country, we want to see the numbers for that country. But we don't want any of the other filters to apply.

Yes you can do that using the Views API. The above task is a real world use case from my latest project and I'd like to share some insights into the API learnt from it. This will be a tutorial and not a lecture about Views architecture, design patterns, and other more esoteric topics.