The notion of a surface braid was defined by Viro
and extensively studied by Kamada.
There exists a one-to-one correspondence between
the set of (equivalence classes of) surface braids and
each of the following two sets,
and many results are obtained by using the correspondences.
One is the set of (slide equivalence classes of) braid systems,
where a braid system is a sequence of elements of
the one-dimensional braid group.
The other is the set of (C-move equivalence classes of) charts,
where a chart is a graph in a two-dimensional disk.
In this talk, we define a canonical form of braid systems,
and prove that any braid system can be deformed into
a canonical form up to slide equivalence.
Though either of braid systems or charts were used
in many of previous studies, we obtain the following as an application
by interpreting the canonical form of braid systems in terms of charts:
Any surface braid can be deformed into an unknotted one
by doing some operations, called crossing changes.
(Iwakiri has a different proof of the above application.)