Query Processing in Dynamic Federation for Loosely-Coupled and Tightly-Coupled Systems.

Date of Submission

December 1996

Date of Award

Winter 12-12-1997

Institute Name (Publisher)

Indian Statistical Institute

Document Type

Master's Dissertation

Degree Name

Master of Technology

Subject Name

Computer Science


Computer and Statistical Services Centre (CSSC)


Bagchi, Aditya (CSSC-Kolkata; ISI)

Abstract (Summary of the Work)

A federated database system (FDBS) is a collection of autonomous databases where each member has local query processing facility for its own users and in addition, they can share certain global queries that are decomposed and distributed among the different members of the federation. Heimbigner & McLeod [1]considered a federated architechture as a loosely coupled structure which does not support interdatabase dependencies and does not have a global schema either. Sheth & Larson(2) on the other hand, described the federated system with much broader capabilities. Depending on the degree of autonomy present among the component databases, they classified FDBS as loosely-coupled and tighty coupled systems. A tightly coupled system would definitely specify interdatabase relationships and would have a global schema. Larson et.al|5) identified the conflicts present among the participating databases. Besides identifying conflicts, Ozsu and Valduriez[3] also described the different stages of integration in a heterogeneous environment. However, all the proposals and rescarch effort referred so far believe in the existence of all the component databases before the federation is built.Bagchi(4] proposed a dynamic environment of Data Federation in which the component databases may join the federation or withdraw from it without affecting the transactions currently running. Component databases not involved in this dynamic change should continue to process their queries. While each component has its own local queries they should maintain a federation to model an organisational setup and thus would provide a structure for shared access. So a global query to the federated structure should be decomposed and distributed among the component databases. During processing, a participating database should not differentiate between a query local to itself and a sub-query assigned to it by adecomposed global query. A dynamic federation demands that a federated structure should grow and shrink with addition or deletion of a database. Some applications need such a structure.1.2 MotivationWe normally form a single database for an enterprise (An enterprise is a reasonably self-contained,commercial,scientific or any other organisation). In a relational system we can update the schema by adding new attributes to a relation or by forming a new relation ac- cording to the requirement. Update also includes deletion of attributes or relations. The above considerations, which can be modelled by a single database, has the following limitations :1. A large enterprise in general consists of a number of sub-enterprisos. Though these sub- enterprises contain overlapping information(some relations are fully or partially common in the sense that they refer to same set of attributes), each such sub-enterprises may be large enough so as to be considered as a separate database.2. Each sub-enterprise has users who are interested only with information related to that sub-enterprise and may not be interested in others.3. Each database may need local autonomy for efficient maintenance and query processing4. Sub-enterprises should act independent to each other, so that error/crash in one should not hinder the local operations in other sub-enterprises.


ProQuest Collection ID: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqm&rft_dat=xri:pqdiss:28843218

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Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.



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