A set of constraints visualized as a sparse alignment. In each species, positions increase from left to right with respect to the partial order. Sequence positions in the same column are equal under the partial order. A set of xk, yk separations breaks the sparse alignment into a set of blocks. Positions xk-1, yk-1 and xk, yk define block k, which is composed of the core k (light gray) and the adjacent separation (dark gray).
Roskin et al. BMC Bioinformatics 2011 12:144 doi:10.1186/1471-2105-12-144