[ont.events] U of Toronto Computer Science seminar, Nov. 15

clarke@csri.toronto.edu (Jim Clarke) (11/02/88)

      SYSTEMS SEMINAR - Tuesday, November 15,  2.00 p.m.  in  SF 1105

         (SF = Sandford Fleming Building, 10 King's College Road)

                           Prof. Susan Davidson
              Department of Computer and Information Science
                        University of Pennsylvania

               "Approximate Queries in Incomplete Databases"

Abstract: A new definition of complex objects is introduced which provides
a denotation for incomplete tuples as well as partially described sets.
Set values are ``sandwiched'' between ``complete'' and ``consisitent''
descriptions, allowing the maximal values to be arbitrary subsets of maxi-
mal elements in the domain of the set.  A form of rules is also introduced
which define queries over these objects.

An interesting property of the inference rules is that they are monotone.
The method can therefore be used to improve the fault-tolerance and predic-
tability of response in database systems by guaranteeing a ``correct'' ap-
proximate answer to a query at any point in computation.  These approximate
answers improve monotonically with time in the sense that any fact which is
said to be true remains true as computation proceeds, and any fact which
can be inferred to be false remains false as computation proceeds.
-- 
Jim Clarke -- Dept. of Computer Science, Univ. of Toronto, Canada M5S 1A4
              (416) 978-4058
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