Associating a VHDL RECORD with a buffer

I am storing some data into a array of

STDV type my_array is array(0 to 7) std_logic_vector(7 downto 0);

signal datain : my_array;

type my_record is record a : std_logic_vector(7 downto 0); b : std_logic_vector(7 downto 0); etc end record.

signal header : my_record;

How do I associated the "header" with datain? Data comes into my code and I save it into an array as follows: datain[0]