I got a shapefile with contours, but no elevation data is present. We can assume as known info, that the contours mark elevations at known steps (say, 20 m). Is it still possible to restore the elevation information and build the DEM model of relief, assigning arbitrarily the 0 elevation value to some starting contour? (either in ArcMap, or in QGis/Grass)
One solution would be to convert your contours into points at a certain interval (I'm not sure how to select the interval objectively) and do a co-kriging interpolation, using an auxilary layer like a remotely sensed image of the area or other closely related variable with elevation (land cover might do too).