Relationship of parts of a bigger building complex e.g. shopping mall or train station / airport

Dear all, i want to render a map related to a bigger venue / building which contains other smaller entities. Take a mall or a train station and their respective shops and parking as an example.

Some elements e.g. for a train station are covered by the public transport relations, however in particular the shops are usually not.

What is the best way to filter the XML to all elements that belong to a logical building? As far as i'm aware it is not allowed to map a relationship as a building (https://wiki.openstreetmap.org/wiki/Key:building) so how would you do this?