Often users of database systems submit queries reflecting certain assumptions
that they have made about the information contained in the system. For
example, a user may ask the question: "Is Jack's brother older than 25 years?"
The query is clearly based on the presumption that Jack has a
brother. Consider the case in which Jack has no brothers. Then the answer "no"
this query is misleading because it may be interpreted by the user as "Jack
has a brother who is not older than 25 years of age." The SEAVE mechanism
described in this paper attempts to address this problem by extracting
presuppositions from the queries that result in a null value. By finding the
presuppositions, the system is capable of providing informative answers (more
than just null) to those queries that are based on erroneous assumptions. The
paper gives a lengthy introduction to the problem, describes how
presuppositions may be extracted from queries, presents a method for testing
presuppositions against the contents of the database, and finally provides
algorithms for the implementation of SEAVE with a relational database
system. The paper is informal and does not contain any proof of
correctness. The obvious advantage of SEAVE is the improvement of
communication between users and systems. However, the improvement is achieved
at a high cost of computing and testing presuppositions.
<p>
Forouzan Golshani<br>
<em>ACM Computing Reviews</em>