Is there any "set" database? For example Neo4j is a "graph" database. What I'm looking for is database which can be used to organize "items" into "sets" and then be able to query them with set operations. For example "items that are in set A and B but not in set C".
Or which one of current databases can efficiently do this data modeling?
Sets are not limited, they can be added/edited/removed as data, just like items or like links in a graph database. For example making a new set called D or Set2347 and add some item in it.
An example would be pages liked by users, where each page is a "set" which is liked by users as "items" it contained.
To clarify my question I would better quote Karl Bielefeldt comment:
The question isn't whether it's possible to use a relational database for this use case. Obviously it is. It's possible to use a relational database for a graph, but we have graph databases anyway which make working with graphs a lot easier. Asking if something similar exists for sets is not an unreasonable or unclear question, even if the answer happens to be no. Maybe people have some good ways to make working with sets on relational databases easier.