The top-level headers are named after the library:

    #include <libebackend/libebackend.h>
    #include <libebook/libebook.h>
    #include <libecal/libecal.h>
    #include <libedata-book/libedata-book.h>
    #include <libedata-cal/libedata-cal.h>
    #include <libedataserver/libedataserver.h>
    #include <libedataserverui/libedataserverui.h>

Including individual headers will cause a compilation error.