Please help explain #include <> non system file

Please help explain on pacman source code ready on home repo In pacman directory it has some #include <> non system file e.g. #include <alpm.h> Why should it be that path why not it refes to this local pacman code project e.g. #include <../lib/libalpm/> Is it different or is actually function the same ? it's so confusing, please help out!