From: Alexander Moshchuk (anm@cs.washington.edu)
Date: Mon May 03 2004 - 10:16:29 PDT
Information integration using logical views
The paper reviews the theory behind view-based information integration
approaches, and then compares two information integration systems -
Information Manifold (IM) and Tsimmis.
The paper starts out by reviewing conjunctive queries and datalog, the
idea of containment and how to test for it, and extensions with
negation and arithmetic comparisons. Conjunctive query containment
can be used in information integration for "converting" between
queries on underlying base relations and queries on views.
Next, the paper describes two information integration systems, IM and
Tsimmis. IM is based on a single global set of predicates that are
used to express all queries and views. Tsimmis is built on an
architecture that allows creating a hierarchy of many connectable
mediators that are used for querying. It is based on an
object-oriented data model and uses a query language MSL which has
some resemblance to XML in the way it handled data. The mediators
must be carefully defined, otherwise they might be awkward to use for
queries as the author illustrates. Even though both systems are based
on the same conjunctive query theory, the author notes some
differences between them, namely query translation (global predicates
vs. mediators), level of mediation (two in IM vs. infinity in
Tsimmis), scalability (adding/maintaining is much easier in IM), and
support for semistructured data by Tsimmis but not IM (very important
for today's web applications).
I really appreciated all the examples given in the paper, which made
the theory much easier to understand. I wonder if the two described
approaches for information integration could be combined somehow,
getting the best of both worlds.
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