Lists and categories can be defined with properties that can be used to run a query. Important is that the inverse is true as well. A Wikipedia list or category implies that particular statements are true for the items that exist on a list or in a category.
A category like "Actors in Hindi cinema" indicates:
- "instance of" "human"
- "profession" "actor / actress"
- "language" "Hindi"
It does not imply that these actors have the "nationality" of "India". This is implied by the category "Indian film actors".
Thanks to WDQ, it is possible to know which actors who play in Hindi movies do not have the Indian nationality. This query makes it possible for people who care about Bollywood to consider the nationality of the 224 actors who fit this query.
This describes actionable information of a project. Your project can be done in the same way. You add data using AutoList or WD-Fist and Reasonator will display the information in an attractive way. These are tools that provide you grip on your projects. Wikidata provides you with information that may exist in any or none of the Wikipedias.