digraph services {
{rank=same; rankdir=TB; pages}
{rank=same;  db_manager}
{rank=same; user_manager; mail_manager; search_manager}
{rank=same; db}

pages -> mail_manager [label="Msg"]
mail_manager -> pages [label="Msg"]
search_manager -> pages
mail_manager -> search_manager [label="Msg"]
db_manager -> mail_manager  [label="Msg"]
db_manager -> user_manager [label="User"]
user_manager -> pages [label="User"]
pages -> user_manager [label="User"]
user_manager -> mail_manager [label="User"]
mail_manager -> user_manager [label="User"]
db_manager -> db [label="raw data"]
}