erd               = "diagram" [ identifier ] "{" entities relationships "}" .
entities          = "entities" "{" { entity } "}" .
entity            = identifier "{" { fields } "}" .
fields            = field { "," field } .
field             = identifier [ "*" ] .
relationships     = "relationships" "{" { relationship } "}" .
relationship      = quantifier [ "," quantifier ] identifier identifier
                    quantifier [ "," quantifier ] identifier .
identifier        = word-identifier | quoted-identifier .
word-identifier   = letter { letter } .
quoted-identifier = "'" word-identifier "'" { quoted-identifier } .
quantifier        = "0" | "1" | "m" | "n" .
letter            = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J"
                  | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T"
                  | "U" | "V" | "W" | "X" | "Y" | "Z"
                  | "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j"
                  | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | "s" | "t"
                  | "u" | "v" | "w" | "x" | "y" | "z"
                  | "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

$ ./emlc --help
ERD Maker Language Compiler v0.9
usage: emlc {options}
options:
-i,--input      Input filename. If not specified, read from standard input 
                without waiting
-o,--output     Output filename. If not specified, write to standard output
-h,--help       Show this message

diagram 'My Library''s Schema' {
  # id is primary key of every entity
  entities {
    users { id*, name, 'join date' }
    books { id*, title, 'release date' }
    authors { id*, name }
  }
  # This is an example of one to many
  # and many to many relationships
  relationships {
    1 users borrow 0,m books
    m books 'written by' 1,n authors
  }
}

graph "My Library's Schema" {
  labelloc="t";
  label="My Library's Schema";
  overlap="scale";
  splines="true";
  e_users [label="users",shape=box];
  f_e_users_id [label=<<u>id</u>>,shape=ellipse];
  f_e_users_id -- e_users;
  f_e_users_name [label="name",shape=ellipse];
  f_e_users_name -- e_users;
  f_e_users_join_date [label="join date",shape=ellipse];
  f_e_users_join_date -- e_users;
  e_books [label="books",shape=box];
  f_e_books_id [label=<<u>id</u>>,shape=ellipse];
  f_e_books_id -- e_books;
  f_e_books_title [label="title",shape=ellipse];
  f_e_books_title -- e_books;
  f_e_books_release_date [label="release date",shape=ellipse];
  f_e_books_release_date -- e_books;
  e_authors [label="authors",shape=box];
  f_e_authors_id [label=<<u>id</u>>,shape=ellipse];
  f_e_authors_id -- e_authors;
  f_e_authors_name [label="name",shape=ellipse];
  f_e_authors_name -- e_authors;
  r_e_users_borrow_e_books [label="borrow",shape=diamond];
  e_users -- r_e_users_borrow_e_books [label="1"];
  r_e_users_borrow_e_books -- e_books [label="(0,m)"];
  r_e_books_written_by_e_authors [label="written by",shape=diamond];
  e_books -- r_e_books_written_by_e_authors [label="m"];
  r_e_books_written_by_e_authors -- e_authors [label="(1,n)"];
}