This question is broad and not very clear -- with the result that the following answers cover quite different scenarios and use cases.

Functional UNIX[edit] Broadly, any Unix-like system that behaves in a manner roughly consistent with the UNIX specification, including having a "program which manages your login and command line sessions";[14] more specifically, this can refer to systems such as Linux or Minix that behave similarly to a UNIX system but have no genetic or trademark connection to the AT&T code base.

In a broader sense, taxonomy also applies to relationship schemes other than parent-child hierarchies, such as network structures. Taxonomies may then include a single child with multi-parents, for example, "Car" might appear with both parents "Vehicle" and "Steel Mechanisms"