Binary Coded Decimal (BCD) to Seven Segment Display Behavioural Modelling

LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
USE IEEE.STD_LOGIC_ARITH.ALL;
USE IEEE.STD_LOGIC_UNSIGNED.ALL;

ENTITY bcd_to_ssd IS
    PORT (
        b : IN STD_LOGIC_VECTOR (3 DOWNTO 0);
        y : OUT STD_LOGIC_VECTOR (6 DOWNTO 0));
END bcd_to_ssd;

ARCHITECTURE Behavioral OF bcd_to_ssd IS

BEGIN
    PROCESS (b)
    BEGIN
        CASE b IS
            WHEN"0000" => y <= "1111110";
            WHEN"0001" => y <= "0110000";
            WHEN"0010" => y <= "1101101";
            WHEN"0011" => y <= "1111001";
            WHEN"0100" => y <= "0110011";
            WHEN"0101" => y <= "1011011";
            WHEN"0110" => y <= "1011111";
            WHEN"0111" => y <= "1110000";
            WHEN"1000" => y <= "1111111";
            WHEN"1001" => y <= "1111011";
            WHEN OTHERS => NULL;
        END CASE;
    END PROCESS;
END Behavioral;