Syntactic Characterisations of Polynomial-Time Optimisation Classes (Syntactic Characterizations of Polynomial-Time Optimization Classes)

In Descriptive Complexity, there is a vast amount of literature on decision problems, and their classes such as P, NP, L and NL. However, research on the descriptive complexity of optimisation problems has been limited. Optimisation problems corresponding to the NP class have been characterised in terms of logic expressions by Papadimitriou and Yannakakis, Panconesi and Ranjan, Kolaitis and Thakur, Khanna et al, and by Zimand. Grädel characterised the polynomial class P of decision problems. In this paper, we attempt to characterise the optimisation versions of P via expressions in second order logic, many of them using universal Horn formulae with successor relations. The polynomially bound versions of maximisation (maximization) and minimisation (minimization) problems are treated first, and then the maximisation problems in the “not necessarily polynomially bound” class.