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ditributed databases


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ditributed databases and transparency of ddb

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ditributed databases

  1. 1. BrAinY 4 Presented to:- Ma’am Asima Jamil & Class GROUP MEMBERS Zupash Sana Marhaba GROUP LEADER Hira Anwar
  3. 3. Topics to be discussed are  Centralized database system  Distributed database  Decentralized database  Distributed DBMS  Advantages and disadvantages of DDBMS  Distributed database design  Function of DDBMS  Types of DDBMS  DBMS transparency & gateways
  4. 4.  Centralized DB system  Distributed DB system  Decentralized DB system  Distributed DBMS Presented by ZUPASH KIRAMAT
  5. 5. Centralized Database system A centralized database sometimes abbreviated CDB) is a database that is located, stored, and maintained in a single location.This location is most often a central computer or database system, for example a desktop or server CPU, or a mainframe computer
  6. 6. Distributed DB system  database In a Distributed Database System the database is stored/spread physically across computers or sites in different locations that are connected together by some form of data communication network.
  7. 7. Distributed DB system
  8. 8. Difference
  9. 9. Decentralized DB system Database is stored on computers or sites on different location but the computers are not interconnected via a network.
  10. 10. Distributed DBMS  A DDBMS is a centralized application that manages a distributed database as if it were all stored on the same computer.  Synchronizes all the data periodically, and in cases where multiple users must access the same data.
  12. 12. ADVANTAGES  Local control  Reliability and availability  Efficient querying process  Modular growth  Economics
  13. 13. Advantages…
  14. 14. Disadvantages  Software complexity and high costs  Processing overheads  Data integrity  Complex DB design  Slow response
  16. 16. Distributed DB design Three additional factors are involved 1.Data Fragmentation 2.Data replication 3.Data allocation
  17. 17. Distributed Database Design  Fragmentation  Relation may be divided into a number of sub-relations, which are then distributed.  Allocation  Each fragment has to be allocated to one or more sites.  Replication  Copy of fragment may be maintained at several sites.
  18. 18. Fragmentation  The DB may be broken into logical units. Types  Horizontal fragmentation • table broken into two or more set of rows.  Vertical fragmentation • table broken into two or more set of columns
  19. 19. 41 Horizontal and Vertical Fragmentation
  20. 20. Data replication  A copy of each fragment may be stored at several sites.  Data replication is the design process of deciding which fragment will be replicated.
  21. 21. Data Allocation  Each fragment have to be allocated to one or more sites, where it will be stored.  Three strategies used for this purpose: 1. Fragmented data allocation. 2. Complete replication 3. Selective replication
  22. 22. Fragmented data allocation.  Database partitioned into disjoint fragments, each fragment assigned to one site.  Also called non-redundant allocation or partitioned allocation. Advantages: 1. Efficiency 2. Security Disadvantages 1. Inconsistent access speeds 2. Backup vulnerability
  23. 23. Complete replication  A complete copy of DB is maintained at each site.  No replication. ADVANTAGES: 1. Faster and consistent access speeds 2. Reliability 3. Node decoupling DISADVANTAGES: 1. Update complexity 2. Increased storage requirements
  24. 24. Selective Replication  Combination of partitioning, replication, and centralization.
  25. 25. Functions of DDBMS  EXTENDED COMMUNIICATION SERVICES: provides access to remote sites and allow transfer of queries.  EXTENDED SYSTEM CATALOG: (Global system catalog) to store data distribution details,  DUSTRIBUTED QUERY PROCESSING:Translate request at one site using local DBMS into proper request to another site using a different DBMS and data model.  EXTENDED CONCURRENCY CONTROL: to maintain concurrency of the replicated data.  EXTENDED RECOVERY SERVICES: to be able to recover from individual site crashes and failure of communication links.
  26. 26. TYPES OF DDBMS marhaba wazir
  27. 27. What is it? Cheerios
  28. 28. What is it? Trail Mix
  29. 29. Types of Distributed Database System  Homogeneous  Heterogeneous DDBMS Homogenous Heterogeneous
  30. 30. Homogenous Distributed Database Systems  In this type of database has all data center have same software  Much easier to design and manage.  It appears to user as a single system
  31. 31. characteristics  Data are distributed  Same DBMS is used  Data managed by distributed DBMS  Users access database through one schema  Global schema is the union of all local DB schemas
  32. 32. Homogeneous Database Same software
  33. 33. Heterogeneous Distributed Database Systems In this type of database , Different data center may run different DBMS products, with possibly different underlying data models. CHARACTERISICS • Data is distributed across nodes. • Different DBMS is used • Only local access databases can be accomplished using only local DBMS and schema. • A global schema exists.
  34. 34. Heterogeneous Distributed database Sql oracle
  35. 35. DBMS transparency & Gateways  Transparency refers to ability to hide the knowledge that local DBMSs may be different.  Applies to heterogeneous environment.  To achieve transparency, DBMSs at different sites should support the same interface.
  36. 36. Gateways Gateway provides following functions.  Protocol for exchange of information between two DBMSs.  Mapping between two DBMSs data types.  Mapping the SQL of the X system to that ofY.  Mapping feedback information if theY system to that of the X.  an effective mechanism to synchronize locking and commit mechanism ofY system with those requested by X system.  Provide relational server function for theY DBMS.
  37. 37.   ems&espv=2&biw=1440&bih=799&source=lnms&tbm=isch&sa=X&ved=0CAYQ_AUo AWoVChMI0Oj2vIWJyQIVxDSUCh2jVQ9q&dpr=1  ie=UTF-8#q=horizontal+and+vertical+fragmentation 