Aesthetic Evaluation

Birkhoff:

M = O / C

Where O is the degree of order of the work, C is the degree of complexity, and M is the aesthetic measure.

Gips & Stiny:

E_z<α, β> = L(β) / L(α)

Where <α, β> is an interpretation of a work, L(α) is the length of the input component of the interpretation and L(β) is the length of the output component of the interpretation, and E_z<α, β> is the aesthetic value assigned to the interpretation.