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By Paul Murray Claire McQuade Kashif Rafiq David Miller 1 Introduction Federated Databases (FDBSs) Key areas Characteristics of DBS/FDBS Architecture Views 2 Characteristics - of DBS • Distribution • Autonomy • Heterogeneity 3 Characteristics - Autonomy Transaction Control Query Processing Distribution of Control Degree to which individual DBMS can operate independently Logically Integrated Multiple DBMS low Federated DBMS Autonomy Multidatabase System High 4 Characteristics-Distribution Deals with data Single DBS Many DBSs in a local area network Many DBSs in a wide area network Multiple Sites Single DBS Local Distribution Distributed 5 Characteristics-Distribution Data and the Federated Database System (FDS) Databases may be on the same computer Databases may be geographically separate Systems must be able to communicate Benefits of distribution Improved access times Improved availability Improved reliability 6 Characteristics -Heterogeneity Data models Structures Constraints Query languages 7 Characteristics of FDBS Collection of cooperating but autonomous component database systems (DBSs) Component DBSs integrated to various degrees FDBMS Software that provides controlled and coordinated manipulation of the component DBSs No centralized control 8 Types of FDBS Multidatabase System Nonfederated DBS Federated DBS Loosely coupled Tightly coupled Single Federation Multiple Federation 9 Components of FDBS Federated Database System System 1 System 2 System N DBMS (centralised) DBMS (distributed) DBMS (FDBS) 10 Architecture Processor Coupling Schemas 11 Architecture - Processor Transforming Processors Filtering Processors Constructing Processors Accessing Processors 12 Transforming Processors SCHEMA A TRANSFORMING PROCESSOR Command Translation Schema Translation SCHEMA B 13 Filtering Processors SUBSET OF SCHEMA A FILTERING PROCESSOR Control Commands Control Data SCHEMA A 14 Constructing Processors SCHEMA A CONSTRUCTING PROCESSOR SCHEMA B SCHEMA C 15 Accessing Processors COMMANDS ACCESSING PROCESSOR DATA DATABASE 16 Architecture - Coupling Loosely Coupled FDBS Tightly Coupled FDBS 17 Architecture - Schema Schema Models Five layer model Seven layer model Schema evolution 18 Schema - Five-Level External Schema Export Schema External Schema External Schema Federated Federated Schema Schema Export Schema Export Schema Component Schema Component Schema Local Schema Local Schema Component DBS Component DBS 19 Schema-Five-Level Processor External Schema External Schema Filtering Processor Filtering Processor Federated Federated Schema Schema Constructing Processor Constructing Processor Export Schema Export Schema Filtering Processor Filtering Processor Component Schema Component Schema Transforming Processor Transforming Processor Local Schema Local Schema Component DBS Component DBS 20 Schema - Evolution One of the problems found with federated databases is the cumulative schema evolution rate A client application cannot be tied to a specific integrated view of the federation, as all it takes is one member of the federation to change its schema without ensuring backward compatibility to cause serious problems 21 Semantic - Integrity Constraints The federated database schema should correctly reflect the semantics of the component database schemata of which it is composed Since the semantics of a database schema is also determined by a set of semantic integrity constraints, a correct schema integration has to deal with integrity constraints existing in the different component database schemata 22 Architecture - Views Selection Projection Join Real 23 Conclusion 24