23fl9ddbFragmentation

23fl9ddbFragmentation - DISTRIBUTED DATABASES Prof.Sin-Min...

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DISTRIBUTED DATABASES Prof.Sin-Min LEE Dept. of Computer Science
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Distributed Databases A Distributed Database system stores data across several sites, and each site is typically managed by a DBMS that is capable of running independently of the other sites.
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DEFINITION OF NETWORK DATABASE Network database : is a data which is an organized collection of data elements and their relationships, that presents a systematic user interface.
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ADVANTAGES Its speed and efficiency when traversing. * The chain links provide direct to disk or memory * The chain links provide direct to disk or memory addresses of related records. addresses of related records. * Allows immediate retrieval without the overhead of * Allows immediate retrieval without the overhead of relational choices. relational choices. * Recursive object-oriented attributes searches. * Recursive object-oriented attributes searches. * Deductive inferences. * Deductive inferences. We can write network queries involving recursive relationships through an unbounded number of level.
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DISADVANTAGES Must manipulate the data from a host programming language. Be the complicated nature of the relationship maintenance structure.
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Are they related? The only relationship: distributed database and multi-media databases are technologies in multi-user database processing. Price-performance ratio of computers has dramatically fallen. i.e. cheaper and better. Increased physical separation of computer users of the same database system.
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Distributed database Definition: A database is only a distributed database if its data are distributed. A distributed system is not necessarily a distributed database system. A client-server system is not a distributed database system, because applications processing (or DBMS) has been distributed among multiple client computers, but database still resides in the central server .
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Distributed Database System (simplified) among 4 computers
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Distributed Database Alternatives Unified Distributed Database Database Single Partitioned Nonpartitioned Partitioned Nonpartitioned Nonreplicated Replicated Replicated Parallelism, independence,flexibility & availability - + Expense, complexity, difficulty of control, & risk to security - +
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Main points: Distributed database is desirable mainly because the distributed system mirrors the structure of an enterprise. Local data are kept locally while at the same time remote data can be accessed through a network when necessary. A successful distributed system must be relational. Fundamental principle: To the user, a distributed system should look exactly like a nondistributed system.
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Twelve Rules/Objectives: 1. Local autonomy: 2. No reliance on a central site 3. Continuous operation 4. Location independence/transparency 5. Fragmentation independence 6. Replication independence 7. Distributed query processing 8. Distributed transaction management 9. Hardware independence 10. Operating system independence 11. Network independence 12. DBMS independence
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23fl9ddbFragmentation - DISTRIBUTED DATABASES Prof.Sin-Min...

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