Principles: Opacity: Don´t peek inside

DO: make URIs mnemonic when it´s convenient
DON´T: depend on finding metadata in URIs
DON´T: search engine hueristics about URLs with ´?´ in them
- http://pto.us/showPatent?num=2392839
DON´T: depend on file extensions in URLs (foo.html)
war story: text/* and java...