Froebel’s Gifts were meant to be given in a particular order, growing more complex over time and teaching different lessons about shape, structure and perception along the way. A soft knitted ball could be given to a child just six weeks old, followed by a wooden ball and then a cube, illustrating similarities and differences in shapes and materials. Then kids would get a cylinder (which combines elements of both the ball and the cube) and it would blow their little minds. Some objects were pierced by strings or rods so kids could spin them and see how one shapes morphs into another when set into motion. Later came cubes made up of smaller cubes and other hybrids, showing children how parts relate to a whole through deconstruction and reassembly.
These perception-oriented “Gifts” would then give way to construction-oriented “Occupations.” Kids would be told to build things out of materials like paper, string, wire, or little sticks and peas that could be connected and stacked into structures.
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.