Spanning Tree - Web site

0 /zoo
 1 /zoo/tableOfContents.html
  2 /zoo/mammal/
  2 /zoo/mammal/anteater.html
  2 /zoo/fish/
  2 /zoo/fish/barracuda.html
  2 /zoo/bird/
  2 /zoo/bird/cassowary.html
 1 /zoo/mammal/
   2 /zoo/mammal/anteater.html
 1 /zoo/fish/
   2 /zoo/fish/barracuda.html
 1 /zoo/bird/

hierarchy implicit in URLs

"orphan" nodes collect at the top