An arc of a graph is an oriented edge and a 3-arc is a 4-tuple (v,u,x,y) of
vertices such that both (v,u,x) and (u,x,y) are paths of length two. The
3-arc graph of a graph G is defined to have vertices the arcs of G such
that two arcs uv,xy are adjacent if and only if (v,u,x,y) is a 3-arc of
G. In this paper we give a characterization of 3-arc graphs and obtain sharp
upper bounds on the domination number of the 3-arc graph of a graph G in
terms that of G