  In the area of graph drawing, the One-Sided Crossing Minimization Problem
(OSCM) is defined on a bipartite graph with both vertex sets aligned parallel
to each other and all edges being drawn as straight lines. The task is to find
a permutation of one of the node sets such that the total number of all
edge-edge intersections, called crossings, is minimized. Usually, the degree of
the nodes of one set is limited by some constant k, with the problem then
abbreviated to OSCM-k.
  In this work, we study an online variant of this problem, in which one of the
node sets is already given. The other node set and the incident edges are
revealed iteratively and each node has to be inserted into placeholders, which
we call slots. The goal is again to minimize the number of crossings in the
final graph. Minimizing crossings in an online way is related to the more
empirical field of dynamic graph drawing. Note the slotted OSCM problem makes
instances harder to solve for an online algorithm but in the offline case it is
equivalent to the version without slots.
  We show that the online slotted OSCM-k is not competitive for any k greater
or equal 2 and subsequently limit the graph class to that of 2-regular graphs,
for which we show a lower bound of 4/3 and an upper bound of 5 on the
competitive ratio.
