The principle of abstraction is a grouping principle, whereby a hierarchy is adhered to with higher levels of abstraction placed near the top with more specific concepts underneath.
Example
For the teaching (not personnel) organization of a university the levels of abstraction would go something like this:
University
- → Faculty of Science
- — Department of Physics
- – Subject: Physics 101
- • Topic: Fluid dynamics
- – Subject: Physics 101
- — Department of Earth Sciences
- — Department of Biology
- — Department of Physics
- → Faculty of Arts
- — Department of History
- – Subject: Australian History
- • Topic: 1850-1854 Victorian Gold rush
- – Subject: Australian History
- — Department of Philosophy
- — Department of Literature
- — Department of History
- → Faculty of Medicine
- — Department of Immunology
- — Department of Neurosurgery
- — Department of Endocrinology