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@inproceedings{ISWC-2018-optional, author = {Guohui Xiao and Roman Kontchakov and Benjamin Cogrel and Diego Calvanese and Elena Botoeva}, title = {Efficient Handling of {SPARQL} {OPTIONAL} for {OBDA}}, booktitle = {Proc. of the 17th International Semantic Web Conference ({ISWC} 2018)}, series = {Lecture Notes in Computer Science}, volume = {11136}, pages = {354--373}, publisher = {Springer}, year = {2018}, webpdf = {https://www.doc.ic.ac.uk/~ebotoeva/papers/xkccb-ISWC-18.pdf}, }