

In a previous paper, we have introduced an extension of the lightweight Description Logic EL that allows us to define concepts in an approximate way. For this purpose, we have defined a graded membership function deg, which for each individual and concept yields a number in the interval [0, 1] expressing the degree to which the individual belongs to the concept. Threshold concepts C~t for ~∊{<,≤,>,≥} then collect all the individuals that belong to C with degree ~t. We have then investigated the complexity of reasoning in the Description Logic