Uniform Hierarchy
Scheme defines interpretation and structure
<scheme>:<scheme-specific-part>
Hierarchical when desired [Engelbart]
<scheme>://<authority>/<path>?<query>
<scheme>:/<segment>/<segment>/<segment>
<scheme>:<opaque_string>
Name components may be meaningful
http://www.ics.uci.edu/~fielding/talks/
Hierarchy enables relative URI