What is the meaning of type_map and how to use

[liubaoshuai1402]

Dear developers,

I can not understand the meaning of type.raw and type_map.raw files.
If I want to train a model which contain three atom types. For example, H, C, O.
Supposing I have two systems. one system is H2O and the other is CO2.
I use dpdata convert the DFT results into dp format for training.
But I find, in H2O system, atom type 0 is mapped into H, in CO2 system, atom type 0 is mapped into C.
Won't this cause a serious conflict?
If I set the type_map parameter in a input.json, is the order of element meaningful?
That is to say, is H,C,O equal O,C,H ? How should I determine its order ?