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4.2.6.1  State  identification
In  state  identification,  a  distinction  is  made  between  “primary”  and  “derived”  state  variables.  Primary
state  variables  are  based  on  data  types  which  are  supplied  directly  by  sensors.  Derived  state  variables
are  calculated  by  the  combination  of  various  state  variables.  It  should  be  borne  in  mind  that  this  definition ­
  relates  solely  to  the  method  with  which  the  variable  concerned  is  calculated,  and  not  to  the  variable
itself.  For  this  reason  it  is  possible  that  the  same  state  variable  is  considered  both  as  a  “primary”  and
“derived”  state  variable  (see  state  variable  “LATLONxy”:  primary  state  variable  from  the  position  sensor  -
DFD  5.1.1.1  and  derived  state  variable  from  dead  reckoning  -  DFD  5.1.2.4).

DFD  5.1  :  State  identification