What would be a standard way to add warning or error or such similar metadata to an entity of let say IfcElement ?
Are you looking for the BCF standard? What type of warning message are you thinking of?
The closest thing in IFC might be the IfcObjective classes. Otherwise, the description field, or custom pset depending on your usecase.
I want to check elements if they have certain properties assigned to them(geometry or different properties like height, weight and so on) . If they are not set, mark them for instance add the list of the unassigned properties to that entity(?) , so the BIM coordinator/manager knows of the problem
I never used BCF and am only roughly familiar with the concept. and my guess is that I have to do it by BCF, but am not sure!
I wonder if it is too much for this use case.
You may use BCF for this. But you’d be right in thinking it is a bit overkill.
The better solution for this is to use an MVD and check with that. However, the current state of MVDs has quite a few problems, meaning that it is not a straightforward task for an end-user to write their own MVD.
An easier solution is to write a series of requirements tests, such as those that Solibri offer you, or SimpleBIM. These can check your models for certain property assignments, and produce reports for elements that don’t pass.
If you don’t want to pay for those software, the free and open source software BIMTester lets you do exactly the same thing, and also works cross-platform, as well as headlessly on a server.