Distributed Database Management Systems: Lecture 12. The main topics covered in this chapter include: global schema architecture; 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;...
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 Virtual University of Pakistan • • • Local Schema • 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 Multidatabase Systems: Architectures External Schema External Schema External Schema External Schema Federated Schema Global Schema Federated Schema Schema Integration Export Schema Component Schema • • • Export Schema Export Schema Export Schema Component Schema Component Schema • • • Component Schema Schema Translation Local Schema Local Schema • • • Global Schema Architecture Virtual University of Pakistan Local Schema Local Schema • • • Federated Database Architecture Global Data Dictionary Virtual University of Pakistan • A directory is a database that contains data about data (metadata) • Called global directory in case of a DDBS • Contains mappings 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 • 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 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 DDB Design • Top-Down Design Process • Bottom-Up Design Process Virtual University of Pakistan 10 Requirement Analysis System Requirements (Objectives) User Input Conceptual Design View Design View Integration Global Conceptual Schema Access In formation External Schema Def Distributed Design User Input Local Conceptual Schemas Physical Design Physical Schema Feedback Feedback Virtual University of Pakistan Observation and Monitoring 11 • 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 12 Bottom-Up Design Process External Schema External Schema Global Schema Component Schema Local Schema • • • Component Schema Local Schema • • • Virtual University of Pakistan Multidatabase Architecture 13 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 14 • Disadvantages: – Difficult to manage in case of nonexclusive Fragmentation (replication) – Maintenance of Integrity constraints Virtual University of Pakistan 15 Thanks ... up, where as in logically integrated DDBS it is top-down Virtual University of Pakistan Multidatabase? ?Systems:? ?Architectures External Schema External Schema External Schema External Schema... Pakistan Local Schema Local Schema • • • Federated? ?Database? ?Architecture Global Data Dictionary Virtual University of Pakistan • A directory is a database that contains data about data (metadata)... Pakistan 12 Bottom-Up Design Process External Schema External Schema Global Schema Component Schema Local Schema • • • Component Schema Local Schema • • • Virtual University of Pakistan Multidatabase Architecture