The approximate information retrieval approach finds least upper bounds of a concept and then uses them to get upper approximation of the concept to solve this problem of ontology heterogeneity.However

the current method considers the bounds only containing separate concepts

so it cannot get the least upper approximation of the concept.In this paper

disjunction of the concepts is introduced to define multielement least upper bounds

and the approximation based on them is proved the least upper approximation of a concept.In general

multielement least upper bounds may contain much redundancy

which will increase the expression complexity of the least upper approximation of a concept.We also define the simplified multielement least upper bounds and provide effective algorithm to find them last.