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
He feels the end of the cane Picture a blind man probing his way with a cane. While he is alert to the feelings in the hand holding the cane, the crucial distinction may be defined by saying that these feelings are not watched in themselves, but that he watches something else by way of them, that is, by keeping aware of them. He has a subsidiary awareness of the feelings in his hand, feelings which are merged into a focal awareness at the end of the cane, constituting two kinds of awareness that are mutually exclusive — "from awareness" and "focal awareness". There is here a particularly interesting phenomenal transformation. The sensations of the cane on his hand (the surface of the cane as it touches the palm of his hand, etc.) are lost. Instead, he feels the end of the cane as it touches an object...If our blind man shifts his attention from the tip of his cane to his hand, the meaning on the end of the cane disappears. Michael Polanyi, Personal Knowledge Focal awareness