For the processing of the knowledge available in the Semantic Web are inference engine necessary.
Inference engines deduce new knowledge from already specified knowledge.
Using the first approach one can distinguish between different kinds of representation languages and inference engines. Higher Order Logic Based Inference Engines Higher Order Logics have to greatest expressive power among all known logics. E.g. for the characterization of transitive closure of an relation higher-order logics are needed. However, higher order logics don't have nice computational properties. In contrast, higher-order semantics is manifested by semantic structures in which variables may range over domains of relations and functions constructed out of the domains of individuals.