The TAILNODE statement specifies the SAS variable that must be present in the ARCDATA= data set that has as values the names of tail nodes of arcs. The TAILNODE variable must have character values. It is not necessary to have a TAILNODE statement if the name of the SAS variable is _TAIL_ or _FROM_. If the TAILNODE list variable value is missing, it is assumed that the observation of ARCDATA= data set contains information concerning a nonarc variable.