Distributed Database Management Systems Lecture 12

Global Schema Architecture G External Schema G External Schema Global Schema Schema Integration L External Schema Component Schema Component Schema L External Schema • • • Schema Translation Local Schema Local Schema • • • Virtual University of Pakistan

Virtual University of Pakistan GCSs in MDBS and logically integrated DDBS is different Design process moves in inverse directions, MDBS design process is bottom up, where as in logically integrated DDBS it is top-down Virtual University of Pakistan

Virtual University of Pakistan Multidatabase Systems: Architectures External Schema Global Component • • • Local Global Schema Architecture Federated Schema Export Component • • • Local External Federated Database Architecture Schema Integration Schema Translation Virtual University of Pakistan

Global Data Dictionary Virtual University of Pakistan

Virtual University of Pakistan A directory is a database that contains data about data (meta-data) Called global directory in case of a DDBS Contains mappings Virtual University of Pakistan

Virtual University of Pakistan A single large or multiple for different sites Hierarchies of DD can be built Location: whether to keep at a single site or distributed Single site increases load on that site Virtual University of Pakistan

Virtual University of Pakistan Single copy or replication Replication increases availability and reliability All three issues are orthogonal to each other That concludes our Architecture discussion Lets summarize Virtual University of Pakistan

Virtual University of Pakistan Introduction Schema Design The DDB Design concerns two major steps, Schema Design and Schema Distribution Schema Distribution Distribution of Schema decides the placement of data as well Virtual University of Pakistan

Virtual University of Pakistan DDB Design Top-Down Design Process Bottom-Up Design Process Virtual University of Pakistan

System Requirements (Objectives) Requirement Analysis System Requirements (Objectives) User Input Conceptual Design View Design View Integration Global Conceptual Schema External Schema Def. Access In formation Distributed Design User Input Local Conceptual Schemas Physical Design Physical Schema Feedback Feedback Virtual University of Pakistan Observation and Monitoring

Virtual University of Pakistan Conceptual Design is Global Conceptual Schema View Design results in individual External Schema Definition (Global users) Activities so far are similar to Centralized DB Design Then start the distribution activity Virtual University of Pakistan

Virtual University of Pakistan Bottom-Up Design Process External Schema Global Component • • • Local Multidatabase Architecture Virtual University of Pakistan

Distribution Design Issues Why fragments How should we How much should be fragmented Any way to test correctness Allocation Strategy Required Information Virtual University of Pakistan

Virtual University of Pakistan Disadvantages: Difficult to manage in case of non-exclusive Fragmentation (replication) Maintenance of Integrity constraints Virtual University of Pakistan

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