BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Date iCal//NONSGML kigkonsult.se iCalcreator 2.20.2//
METHOD:PUBLISH
X-WR-CALNAME;VALUE=TEXT:Eventi DIAG
BEGIN:VTIMEZONE
TZID:Europe/Paris
BEGIN:STANDARD
DTSTART:20141026T030000
TZOFFSETFROM:+0200
TZOFFSETTO:+0100
RDATE:20151025T030000
TZNAME:CET
END:STANDARD
BEGIN:DAYLIGHT
DTSTART:20150329T020000
TZOFFSETFROM:+0100
TZOFFSETTO:+0200
TZNAME:CEST
END:DAYLIGHT
END:VTIMEZONE
BEGIN:VEVENT
UID:calendar.7013.field_data.0@diag.uniroma1.it
DTSTAMP:20260403T174028Z
CREATED:20150317T131343Z
DESCRIPTION:The standard theoretical approach to evaluating queries on inco
 mplete databases is to compute certain answers. Their main drawback is ver
 y high complexity of query evaluation. In practice\, SQL relies on three-v
 alued logic for efficiently evaluating queries on databases with nulls\, b
 ut this cannot produce certain answers due to thecomplexity mismatch.If qu
 ery evaluation differs from certain answers\, it can generate either false
  positives (answers which are not certain) or false negatives (i.e.\, miss
  some of the certain answers). The problem with SQL is that it produces bo
 th. Since we cannot eliminate both and have an efficient procedure at the 
 same time\, the best we can hope for is eliminate one kind of wrong answer
 s entirely - then at least the user knows in which way not to trust SQL.We
  show that it is surprisingly simple to fix SQL's three-valued logic to el
 iminate false positives (or false negatives by a dual procedure). In the p
 rocess of doing so we also introduce a new notion of certain answers with 
 nulls\, which properly accounts for queries returning tuples containing nu
 ll values. 
DTSTART;TZID=Europe/Paris:20150331T150000
DTEND;TZID=Europe/Paris:20150331T150000
LAST-MODIFIED:20240620T113644Z
LOCATION:Aula Magna\, DIAG
SUMMARY:SQL's Three-Valued Logic and Certain Answers  - Leonid Libkin\, Uni
 versity of Edinburgh
URL;TYPE=URI:http://diag.uniroma1.it/node/7013
END:VEVENT
END:VCALENDAR