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The need for incremental algorithms for evaluating
database queries is well known, but constructing
algorithms that work on object-oriented databases (OODBs)
has been difficult. The reason is that OODB query languages
involve complex data types including composite objects and
nested collections. As a result, existing algorithms have
limitations in that the kinds of database updates are
restricted, the operations found in many query languages
are not supported, or the algorithms are too complex to
be described precisely.
We present an incremental computation algorithm that
can handle any kind of database updates, can accept
any expressions in complex query languages such as OQL,
and can be described precisely. By translating primitive
values and records into collections, we can reduce all
query expressions into ones composed of only one kind
of operation, namely comprehension. This makes the
problems with incremental computation less complicated
and thus allows us to describe the algorithm precisely.
Our incremental algorithm consists of two parts:
one is to maintain the consistency in each comprehension
occurrence and the other is to update the value of an
entire expression. The algorithm is so flexible that we
can use strict updates, lazy updates, and their combinations.
By comparing the performance of applications built with
our mechanism and that of equivalent hand written update
programs, we show that our incremental algorithm can be
implemented efficiently.
By: Hiroaki Nakamura
Published in: ACM SIGPLAN Notices, volume 36, (no 11), pages 156-165 in 2001
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