The Gajski-Kuhn chart (or Y diagram) depicts the different perspectives in VLSI hardware design. Mostly, it is used for the development of integrated circuits. Daniel Gajski and Robert Kuhn developed it in 1983. In 1985, Robert Walker and Donald Thomas refined it. According to this model, the development of hardware is perceived within three domains that are depicted as three axis and produce a Y. Along these axis, the abstraction levels that describe the degree of abstraction. The outer shells are generalisations, the inner ones refinements of the same subject.