I wanted to mention/describe some features (shops, restaurants, child zones, offices etc.) in some multi-level buildings (malls, commercial centers) as POIs, without creating exact level mapping (possibly adding a mapping later, or leaving it to someone else).
How to do it properly, creating all required nodes/relations?
I have read corresponding topics and viewed some examples but most of them are related to exact 3D modelling. Other information is unclear, incomplete or even controversial. There are many proposals but I’m not sure which of them are really supported.
Where is better to specify a multilingual building name, address, number of levels, min/max level numbers: in building outline or in building relation?
Which role should be specified for each of POIs located on a level?
Is there a good example of a multi-level mall using the latest rendering features?
Generally avoid using relations: the consensus is that they dont help with either 3D or indoor mapping of buildings.
To start you just need to use the level tag (https://wiki.openstreetmap.org/wiki/Level) on each POI mapped. It may help to form a convention, for instance map POIs on the ground floor close to their entrances (or on their entrances) and map POIs on other levels at some other distance so that they dont overlap.
Specify the core details on the building outline.
It may also help for node placement to add internal pedestrian ways (for instance using highway=footway or highway=corridor. This will help in placing node POIs. It’s also useful to walk through a mall & notice repeating elements of the structure (for instance columns): these can be used as an suitable internal reference for node placement, and often determine width of shop fronts. Many (most) malls prohibit photography, so it pays to be discreet in surveying. I’ve found using a mobile phone with audio recording to be useful in this regard.
Relation:building suggests to use it for indoor mapping. Am I right that this relation should be used for exact 2D/3D mapping only, not for simply POI placement?
The relation has some niche use cases in 3D mapping. For indoor mapping it is entirely optional and I would not recommend using it, especially if you only want to map POI.