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.
Engineers seem to have a clear, if usually implicit, model of the process of design. It is usually an orderly model of an orderly process as the engineer conceives it.
The notion that the design process should be modeled as a systematic step-by-step process seems to have first developed in the German mechanical engineering community.
Herbert Simon independently argues for design as a search process in The Sciences of the Artificial. He was motivated to lay out a strictly rational model of design precisely because such a model was a necessary precursor to automating design. His model remains influential even if today we recognize the "wicked problem" of original design as one of the least promising candidates for AI.
In software engineering, Winston Royce independently introduced a seven-step Waterfall Model to bring order to the process. In fact, Royce introduced his waterfall as a straw man that he then argued against, but many people have cited and followed the straw man rather than his more sophisticated models. Even if ironically, Royce's seven-step model must be considered one of the foundational statements of the Rational Model of Design.