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DTSTART:20151025T030000
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RDATE:20161030T030000
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DTSTART:20160327T020000
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UID:calendar.7273.field_data.0@oba.diag.uniroma1.it
DTSTAMP:20260408T215020Z
CREATED:20160329T134604Z
DESCRIPTION:Multiple issues with SQL's handling of nulls have been well doc
 umented. To fix them\, amodification of SQL's query evaluation that elimin
 ates false query answers was proposedin my ICDT 2015 (also TODS 2016) pape
 r\, and shown to retain a good theoretical AC0complexity. Two notable ques
 tions remained though: do false answer occur in real-lifeSQL queries? And 
 can the new evaluation scheme be made practical? We now answer these.Using
  the standard TPC-H benchmark\, we show that false answers are very common
  forsome typical queries.  On the other hand\, the modified evaluation fro
 m ICDT 2015 doesnot work well as it computes very large intermediate resul
 ts. So we designed a new wayof avoiding wrong answers\, based on a differe
 nt idea\, and showed that it works well withbenchmark queries. For half of
  them\, the overhead for correctness was very small\, under4%. For others\
 , we saw either a dramatic improvement of several orders of magnitude\, or
 a slowdown that was still tolerable when correctness is important. I'll ex
 plain how thenew query modification works\, present experimental results\,
  and offer comments on theobserved behavior and on deficiencies of query p
 rocessing in commercial databases thatone needs to overcome to make correc
 t evaluation even more efficient.(Joint work with Paolo Guagliardo)=======
 ===============================================Bio sketch. Leonid Libkin i
 s Professor of Foundations of Data Management in the Schoolof Informatics 
 at the University of Edinburgh. He was previously a Professor at theUniver
 sity of Toronto and a member of research staff at Bell Laboratories in Mur
 ray Hill.He received his PhD from the University of Pennsylvania in 1994. 
  His main researchinterests are in the areas of data management and applic
 ations of logic in computerscience. He has written five books and about 20
 0 technical papers. His awards includea Marie Curie Chair Award and five B
 est Paper Awards. He has chaired programmecommittees of major database con
 ferences (ACM PODS\, ICDT) and was the conferencechair of the 2010 Federat
 ed Logic Conference. He has given many invited conferencetalks and has ser
 ved on multiple program committees and editorial boards. He is an ACMfello
 w\, a fellow of the Royal Society of Edinburgh\, and a member of Academia 
 Europaea.
DTSTART;TZID=Europe/Paris:20160407T140000
DTEND;TZID=Europe/Paris:20160407T140000
LAST-MODIFIED:20190906T124508Z
LOCATION:Aula Magna
SUMMARY:Making SQL Queries Correct on Incomplete Databases - Leonid Libkin
URL;TYPE=URI:http://oba.diag.uniroma1.it/node/7273
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