public int getSourceCount() {
        int ret = 0;
        Iterator<LocalVertex> iter = iteratorOfVertex();
        while (iter.hasNext()) {
            LocalVertex lv = iter.next();
            if (!(lv instanceof LocalPhysicalVertex)) {
                continue;
            }
            LocalPhysicalVertex lpv = (LocalPhysicalVertex) lv;
            if (lpv.getVertex().isSourceModule()) {
                ret++;
            }
        }
        return ret;
    }