functions and relations

Usually, we create programs that do one directional computations, which performs operations on given quantities to produce desired output. In some models, we don't have such one directional operations but we know the relation among quantities like the relation between celsius and fahrenheit, 9C = 5(F - 32). Translating this equation into a traditional computer language will force us to calculate one in terms of another instead of specifying the relation and measuring one when other changes. Programming paradigm where we can specify relations is called logic programming.