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
Levels of Scale Scale refers to how we perceive the size of an element or space relative to other forms around it. All things – a tea cup, a building, language, entire eco-systems – consist of smaller components. It is the relationship of the smaller elements which determines the character and degree of life of the whole. Objects which contain a high degree of life tend to contain a beautiful range of scales within, which exist at a series of well-marked intervals and have clearly recognizable jumps between them. To have good levels of scale, it is extremely important that the jumps between different scales of centers not be too great or too small. Christopher Alexander, The Nature of Order The scale of resolution determines what is seen