@inproceedings{BovaChen17,
 author = {Simone Bova and
Hubie Chen},
 booktitle = {Proceeding of the Twentieth International Conference on Database Theory (ICDT), 
March 21-24, 2017, Venice, Italy},
 note = {<strong>Best Paper Award},
 title = {How many variables are needed to express an existential positive query?},
 year = {2017}
}