  A mixed graph can be seen as a type of digraph containing some edges (two
opposite arcs). Here we introduce the concept of sequence mixed graphs, which
is a generalization of both sequence graphs and iterated line digraphs. These
structures are proven to be useful in the problem of constructing dense graphs
or digraphs, and this is related to the degree/diameter problem. Thus, our
generalized approach gives rise to graphs that have also good ratio
order/diameter. Moreover, we propose a general method for obtaining a sequence
mixed digraph by identifying some vertices of a certain iterated line digraph.
As a consequence, some results about distance-related parameters (mainly, the
diameter and the average distance) of sequence mixed graphs are presented.
