The problem with trees Many systems are organized hierarchically. The CERNDOC documentation system is an example, as is the Unix file system, and the VMS/HELP system. A tree has the practical advantage of giving every node a unique name. However, it does not allow the system to model the real world. For example, in a hierarchical HELP system such as VMS/HELP, one often gets to a lead on a tree such as: HELP COMPILER SOURCE_FORMAT PRAGMAS DEFAULTS only to find a reference to another leaf: Please see HELP COMPILER COMMAND OPTIONS DEFAULTS PRAGMAS and it is necessary to leave the system and re-enter it. What was needed was a link from one node to another, because in this case the information was not naturally organized into a tree. Tim Berners-Lee, Seeing With Fresh Eyes A City Is Not a Tree hierarchywww
Cool URIs don't change An Essay by Tim Berners-Lee www.w3.org What makes a cool URI? A cool URI is one which does not change. What sorts of URI change? URIs don't change: people change them. The User Interface of URLs www
Time and space Tones appear placed and directed predominantly in time from before to now to later. Their juxtaposition in a musical composition is perceived within a prescribed sequence only. Horizontally, the tones follow each other, perhaps not in a straight line, but of necessity in a prescribed order and only in 1 direction – forward. Tones heard earlier fade, and those farther back disappear, vanish. We do not hear them backward. Colors appear connected predominantly in space. Therefore, as constellations they can be seen in any direction and at any speed. And as they remain, we can return to them repeatedly and in many ways. This remaining and not remaining, or vanishing and not vanishing, shows only 1 essential difference between the fields of tone and color. The accuracy of perception in one field is matched by the durability of retention in the other, demonstrating a curious reversal in visual and auditory memory. Josef Albers, Interaction of Color It will not stand still to be pointed at