Onion model

An onion model used in social penetration theory

The onion model is a graph-based diagram template for describing an expanding or extending relationship between several concepts. The name is a metaphor of the layered shells that become visible when you cut open an onion. The outer layers in the model typically add size or complexity incrementally to the central layers.

The onion diagram can be presented as an Euler diagram or a stacked Venn diagram. For the record, a stacked Venn contains a series of sets A₁...A_k where each set A_n is a strict subset of A_n+1 (and by recursion, of all A_m where m > n). However, as the onion is often used as a metaphor, it doesn't necessarily make sense to interpret the contents of an onion diagram literally or mathematically.

This diagram format is supported e.g. by Microsoft PowerPoint's SmartArt wizard under the name of "stacked Venn".

In computing

The onion model in computing is used as a metaphor for the complex structure of information systems. The system is split into layers to make it easier to understand.^[1] A simple example is to start with the program, operating system and hardware layers. Each of these layers can then be subdivided.

See also

• Information security § Defense in depth
• Matryoshka doll
• Social penetration theory § Onion metaphor
• Start With Why § The golden circle

References