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.
It seems this transformation, from physical object to vector of data, is a general and oft-repeated process in the history of technology, where new inventions begin in an early experimental phase in which they are treated and behave as singular individual things, but then evolve into vectors in a diffuse and regimented system as the technology advances and becomes standardized.
In the early history of aviation, airplanes were just airplanes, and each time a plane landed or crashed was a singular event. Today, I am told by airline-industry insiders, if you are a billionaire interested in starting your own airline, it is far easier to procure leases for actual physical airplanes, than it is to obtain approval for a new flight route. Making the individual thing fly is not a problem; inserting it into the system of flight, getting its data relayed to the ATC towers and to flightaware.com, is.