  This paper defines a class of labeled stratified order structures that
characterizes exactly the notion of combined traces (i.e., comtraces) proposed
by Janicki and Koutny in 1995. Our main technical contributions are the
representation theorems showing that comtrace quotient monoid, combined
dependency graph (Kleijn and Koutny 2008) and our labeled stratified order
structure characterization are three different and yet equivalent ways to
represent comtraces.
