Yue Pang 0001 Lei Zou 0001 M. Tamer Özsu Jiaqi Chen Efficient Execution of SPARQL Queries with OPTIONAL and UNION Expressions. 2755-2767 2025 ICDE https://doi.org/10.1109/ICDE65448.2025.00207 conf/icde/2025 db/conf/icde/icde2025.html#PangZOC25 streams/conf/icde