RELATIONS.H

The public symbol file NTKRPAMP.PDB for the original release of Windows 10 tells that the kernel is built with the RELATIONS.H header at

d:\th\minkernel\ntos\io\pnpmgr

and draws from it the following type definitions:

Line Number Type
48 enum IRPLOCK
124 struct _RELATION_LIST
161 struct _PENDING_RELATIONS_LIST_ENTRY

The header RELATIONS.H is not known in any Device Driver Kit (DDK) or Windows Driver Kit (WDK).