Open the Data folder and look for the file:

export_descr_unit.txt

Here is a list of all the units and their attributes. I'll take the triarii as an example

Code:
type			 roman triarii
dictionary	   roman_triarii	  ; Triarii
category		 infantry
class			spearmen
voice_type	   Medium_1
soldier		  roman_triarii, 40, 0, 1
officer		  roman_early_centurion
officer		  roman_early_standard
mount_effect	 horse +4, chariot +4, camel +4
attributes	   sea_faring, hide_forest, can_sap
formation		1, 1, 2, 2, 3, square
stat_health	  1, 0
stat_pri		 7, 7, no, 0, 0, melee, simple, piercing, spear, 25 ,0.73
stat_pri_attr	no
stat_sec		 0, 0, no, 0, 0, no, no, no, none, 25 ,1
stat_sec_attr	no
stat_pri_armour  7, 5, 5, metal
stat_sec_armour  0, 0, flesh
stat_heat		4
stat_ground	  2, 0, 0, 0
stat_mental	  10, disciplined, highly_trained
stat_charge_dist 30
stat_fire_delay  0
stat_food		60, 300
stat_cost		1, 500, 210, 50, 80, 500
ownership		romans julii,romans brutii,romans scipii,romans senate
As you can see here there are two officers. You can have up to thee officers, look at the units for examples of which officers exist.

Hope this helps