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From: ami@kodkod.usc.edu (Ami Motro)
Newsgroups: comp.databases
Subject: Support for imprecise data: survey
Message-ID: <26231@usc.edu>
Date: 30 Jul 90 00:24:33 GMT
Sender: news@usc.edu
Organization: University of Southern California, Los Angeles, CA
Lines: 46

Hello database experts,

I am interested in finding the level of support (if any) in present commercial
database systems for IMPRECISE DATA.

I define imprecise data as any relevant information concerning a data value,
which is available in the absence of the actual data value itself.  
For example,
  1. The data value is unavailable, but is known to belong to a specified set
     (disjunctive data).
  2. The data value is unavailable, but is known to be within a particular 
     range (essentially, same as 1).
  3. The data value is unavailable, but is known to exist (null value).  
     This is the same as 1, except that the "set" is the entire domain.
  4. The data value is unavailable, but may not even apply.
  5. The data value is unavailable, but an approximation is available.

As a simple example, assume an attribute TEL-NO.  In a particular case you may
have 123-4567 (precise data); in another case you may only know that it's
either 123-4567 or 765-4321 (disjunctive); or you may be certain that there is
a telephone number, but not know it (null); or you may not be sure whether a
number exists; or you may only have 345-???? (approximation); and so on.

Things I would like to know include, how does the user describe the imprecise
data to the system? How does the system retrieve in the presence of imprecise
data?  Can the user specify imprecision in queries?  And so on.

If you are thoroughly familiar with a database system, and could comment on its
support for imprecise data (and could afford the time to commit it to e-mail),
I would appreciate hearing from you (even if it's simply "nothing at all is
available in system X").

If in your previous experience you encountered situations (applications) where
you had wished that some such support were available, please describe the
particular application, and the particular "missing feature", and how you
worked around it.

Note that many systems offer some support for null values.  Also, constants
with "wildcards" may be considered imprecise retrieval specifications.

Thanks in advance!  If you are interested, I'll send you a paper on the topic,
when it is completed.

Ami Motro

ami@usc.edu