Ontology is the most widely used tool to integrate semantic into activity recognition. However, besides lack of temporal reasoning, ontology cannot deal with uncertainty . Diaz et al. proposed a fuzzy ontology to solve this limitation. But, fuzzy approach allows more precise knowledge representation rather than deciding among multiple hypotheses and having a more coherent view of the situation .
 N. Díaz Rodríguez, M. P. Cuéllar, J. Lilius, and M. Delgado Calvo-Flores, “A fuzzy ontology for semantic modelling and recognition of human behaviour,” Knowledge-Based Systems, vol. 66, pp. 46–60, Aug. 2014.
 A. Bellenger, S. Gatepaille, H. Abdulrab, and J.-P. Kotowicz, “An Evidential Approach for Modeling and Reasoning on Uncertainty in Semantic Applications.,” in URSW, 2011, pp. 27–38.