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Nowadays, many platforms provide open educational resources to learners. So, they must browse and explore several suggested contents to better assimilate their courses. To facilitate the selecting task of these resources, the present paper proposes an intelligent tutoring system that can access teaching contents available on the web automatically and offers them to learners as additional information sources. In doing so, the authors highlight the description logic approach and its knowledge representation strength that underwrites the modulization, inference, and querying about a web ontology language, and enhanced traditional tutoring systems architecture using ontologies and description logic to enable them to access various data sources on the web. Finally, this article concludes that the combination of machine learning with the semantic web has provided a supportive study environment and enhanced the schooling conditions within open and distance learning.

Single-phase Pr 2 CBr was prepared by heating a mixture of PrBr 3 , Pr and C (1 : 5:3) to 1140 • C for 18 d. The crystal structure was investigated by X-ray single crystal diffraction (space group P6 3 /mmc, a = 3.8071 (3), c = 14.7787(12)Å). In the structure the Pr atoms form C-centered octahedra condensed into Pr 2 C sheets via common edges; these sheets are separated by the Br atoms which are in a trigonal prismatic environment of Pr atoms. Pr 2 CBr is a black shiny compound with metallic conductivity. It is a ferromagnet with T c = 13.8(5) K.

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