Discuss MDBS architecture with a global conceptual schema.
A multi database system (MDBS) is a facility that allows users access to data located in multiple autonomous database management systems (DBMSs).
A multi database system is a software layer on top of existing database systems, which is designed to manipulate information in heterogeneous databases.
Dataset is a collection of strongly related data commonly stored as a data file with or without an index structure. MDBS consist of two or more existing datasets and database.
The MDBMS software layer translates the queries formulated with the help of the global data model and the global conceptual scheme into queries based on the local data model. The local execution delivers of the results back.
To execute global query, the MDBS first translate it into a number of sub queries and converts these sub queries into appropriate local queries for running on local DBMS.
After completion of execution, local results are merged and the final global result for the user query is generated.
An MDBS controls multiple gateway an manages local database through these gateways.
A gateway is a ‘special' program that simulates access from one database to another by coding protocols of interactions, by mapping query dialects and data types, by maintaining catalog of the target and so on.
Multi-database allows users to access and share data without requiring physical database integration.
Multi-database can be homogeneous or heterogeneous.
MDBS can be classified as non-federated MDBS and federated MDBS.
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