Database Reference
In-Depth Information
Figure 4.
3. to assemble the sub-fuzzy query results returned by fuzzy query agents and further process the
assembled results in order to compute the final fuzzy query result.
4. to transform back the format of final fuzzy query result into a format that is acceptable to multi-
database applications. Here again it refers to Global fuzzy Schema to Export Fuzzy Schema Mapping
information.
The responsibilities of fuzzy query agents are:
1. to transform sub-queries into local queries that can be directly processed by the local database sys-
tems. This transformation process refers to Export Schema and Export to Local Schema Mapping
information. This information is supposed to be stored in respective local databases.
2. to transform back (using Export Schema and Export to Local Schema Mapping information) the
local fuzzy query results into a format that is acceptable to the fuzzy query mediator and forward
the formatted results to the fuzzy query mediator.
Sub-queries are independent hence they may be processed in parallel at respective local databases.
This reduces the fuzzy query response time. Fuzzy query agents hide heterogeneous fuzzy query in-
terfaces of local database systems from the fuzzy query mediators. Distributed fuzzy query processing
steps designed for global FTS-SQL queries can be described briefly as follows:
Global FTS-SQL queries are parsed to ensure that they are syntactically correct. Based on the parsed
trees constructed, the queries are validated against the global schema to ensure that all relations and
attributes in the queries exist and are properly used. Given a global FTS-SQL fuzzy query, the fuzzy
query mediator decomposes it into sub-queries to be evaluated by the fuzzy query agents. Here the local
database involved in global FTS-SQL fuzzy query will be determined. Some fuzzy query optimization
heuristics are introduced to reduce the processing overhead. Similar strategies have been adopted for
optimizing queries for other multidatabase systems (Evrendilek, Dogac, Nural and Ozcan, 1997; Finance,
Smahi and Fessy, 1995). Decomposed sub-queries disseminated to the appropriate fuzzy query agents
for execution. Fuzzy query agents further translate the sub-queries to the local database queries and
return the sub-fuzzy query results to the fuzzy query mediator. The fuzzy query mediator assembles the
sub-fuzzy query results and computes the final fuzzy query result if there exist some sub-fuzzy query
operations that could not be performed by the fuzzy query agents.
