01       Beginning Activity
02       Ending Activity
03       Activity
04       Interface Activity (when 2 or more separate networks are combined to create 1 
         network)
05       Summary Activity
06       Milestone
07       Event
08       Constraint - Finish to Start
09       Constraint - Start to Finish
10       Constraint - Finish to Finish
11       Constraint - Start to Start
12       Constraint - Dummy
20       Cost Account Activity
21       Work Package Activity
22       Data Item
PI       Maintenance Period Identifier
PM       Proposed Maintenance Action
SM       Scheduled Maintenance Action
ZZ       Mutually Defined