At close inspection every galaxy appears to have its own individuality.A galaxy can be warped, lop-sided, doubly-nucleated, boxy or disky, ... in its own specific, peculiar way. Hence, for a complete description, galaxy taxonomy may ask for finer and finer classification schemes. However, for some applications it may be more fruitful to let details aside and focus on some global properties of galaxies. One is then seeking to measure just a few quantities for each galaxy, a minimum set of globalobservables that yet captures some essential aspect of these objects. One very successful example of...