file_id	IN:	File identifier returned by Hopen
	tag	IN:	Tag of the data element to be read
	ref	IN:	Reference number of the data element to be read
	data	OUT:	Buffer the element will be read into

	Purpose	Reads the data element for the specified tag and reference number and writes it to the data buffer.
	Return value	Returns the number of bytes read if successful and FAIL (or -1) otherwise.
	Description	It is assumed that the space allocated for the buffer is large enough to hold the data.