Thanks for your comment. Of course one can use a search engine for finding recipes. But using a recipe database one can perform ingredient searches and category searches more easily.
With supercook app you can go through your fridge and say the ingredients that you have and the app will tell you what recipes you can cook https://www.supercook.com/#/recipes
There's another app that works in reverse, you pick what recipes you want then it gives you a shopping list. I think the app was Mealime
Here is an example using RDFox: https://imgur.com/ziZdIzA
My fridge has "noodles, tomatos and butter", But I know only one recipe which calls for "noodles, sauce, oil, optionally cheese". However you put alternatives in the database, if you have tomatos, you can make sauce, if you have butter, you don't need oil.
RDFox correctly says I can still make :spaghetti.
Query:
select DISTINCT ?recipe where { :fridge :item ?x. ?recipe a :recipe. ?recipe :requires ?y. OPTIONAL { ?y :alternative ?z }. FILTER(?x IN (?y, ?z)) }