Database Reference
In-Depth Information
Fuzzy Query Decomposition with Optimization
FTS-SQL allows source options to be attached to their SELECT and WHERE clauses. Hence a strategy
should be evolved to decompose a FTS-SQL fuzzy query to handle different combination of source op-
tions. Therefore, we have designed it to meet the following objectives:
a. Fuzzy query agents are supposed to perform most of the fuzzy query processing tasks in order to
maximize the parallelism in local fuzzy query evaluation.
b. To reduce the sub-fuzzy query results that have to be transferred from the local database sites to
the fuzzy query mediator and heuristic fuzzy query optimization has to be performed. Fuzzy query
response time can be improved with small local fuzzy query results shipped between sites.
c. Since every FTS-SQL operations can't be performed by local database systems, the decomposition
process must consider the capabilities of fuzzy query agents and also determine the portion(s) of
global queries to be processed by the fuzzy query mediator itself. At present we have assumed that
all fuzzy query agents support the usual select-project-join FTS-SQL queries.
WHERE clause with the source option
sameDB
allows the join of tuples from the same local database
only and with the source option
anyDB
it allows the join of tuples from any local database. Based on this
join definition, we derive the decomposition strategies for following two categories of FTS-SQL queries:
FTS-SQL queries with WHERE
< … >
[sameDB]
As per this strategy, we decompose a global fuzzy query into a sub-fuzzy query template and a
global fuzzy query residue. Sub-fuzzy query template is the sub-fuzzy query generated based on the
global schema and it has to be further translated into sub-queries on the export schemas of local fuzzy
databases relevant to the global fuzzy query. The global fuzzy query residue represents the remaining
global fuzzy query operations that have to be handled by the fuzzy query mediator. Since
sameDB
is the
source option of the WHERE clause, all
selection
and
join
predicates on the global FTS relation(s) can be
performed by the fuzzy query agents together with their local database systems. Deriving the
Sub-Fuzzy
query Template
and the
Global Fuzzy query Residue
from a
Global Fuzzy query
may be given as follows:
1. The SELECT clause of Sub-Fuzzy query Template is assigned the list of attributes that appear in the
SELECT clause of Global Fuzzy query, including those which appear in the
aggregate
functions.
2. The FROM clause of Sub-Fuzzy query Template is assigned the global FTS-relations that appear
in the FROM clause of Global fuzzy query.
3. Move the selection and join predicates in the WHERE clause of Global Fuzzy query to the WHERE
clause of Sub-Fuzzy query Template.
4. The Global Fuzzy query Residue inherits the SELECT clause of the original Global Fuzzy query.
It's FROM clause is defined by the union of sub-fuzzy query results. In other words, only operations
to be performed by the Global Fuzzy query Residue are Projections. The WITH clause is retained
in the Global Fuzzy query Residue and performed in the last phase of the fuzzy query processing.
5. The values of α and β in the HAVING clause of the global fuzzy query are assigned to the having
clause of all the sub-queries.
