Return the system lattice visualization as graphviz source.

def graphviz(self, highlight=None, maximal_label=None, topdown=None,
            filename=None, directory=None, render=False, view=False):
        """Return the system lattice visualization as graphviz source."""
        return visualize.featuresystem(self, highlight, maximal_label,
            topdown, filename, directory, render, view)