1. A computer-implemented method for computing a concept materialization of an ontology O, wherein O is a formal explicit description of concepts and roles in a domain of discourse comprising: an ABox A, referring to data elements, called individuals, in terms of asserted or inferred concept assertions, and role assertions, expressing a directed relationship that relates one individual, called source, with a second individual, called target, with respect to a particular role, and a TBox T, referring to schema axioms about concepts and roles, wherein concept materialization refers to computing all entailed atomic concepts of all individuals, wherein entailment is defined according to the semantics of a description language used to specify ontology O, the computer-implemented method comprising the following steps: (1) building an ABox B, being an abstract representation of ABox A, based on equivalence classes of individuals in ABox A, wherein individuals fall into the same equivalence class if they are asserted to the same concepts and if they are the source of the same roles and if they are target of the same roles, wherein the ABox B contains for each equivalence class E a fresh individual I with the same concept assertions as the individuals in E, and for each role R j for which the individuals in E appear as source in a role assertion for R j , a corresponding fresh individual I Rj and a role assertion for role R j with I as source and I Rj as target, and for each role R k for which the individuals in E appear as target in a role assertion for R k , a corresponding fresh individual I Rk and a role assertion for role R k with I Rk as source and I as target; (2) materializing all entailed concept assertions of ABox B with respect to TBox T of the ontology O using ontology reasoning; (3) extending ABox A by adding, if not already included, assertions to obtain ABox A′ so that ABox A′ includes for all equivalence classes E: (i) concept assertions for all individuals of E corresponding to entailed concept assertions for fresh individual I in ABox B representing equivalence class E; (ii) concept assertions for all individuals in ABox A which are source respectively target of a role assertion with role R corresponding entailed concept assertions in ABox B for an individual that is source respectively target of role assertion with role R and an individual I in ABox B representing equivalence class E; (4) if new assertions are added by the extending in step (3) repeat from step (1), wherein ABox A should be the extended ABox A′ provided by step (3); wherein the transformed ontology O′ is obtained from O by replacing the original ABox A with the final extended ABox A′, being a concept materialized version of the original input ABox A.