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Distributed Database Application & System

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					Distributed Database Application
& System
Subject Code: 171602
             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       2
Text Books:

1.Principles of Distributed database systems,
  By M. tamer Ozsu, Petrick Valduriez, Pearson
2.Distributed Database Systems By Chhanda Ray,
  Pearson.

Reference Books:
1.Distributed Databases: Principles and Systems,
  Stefano Ceri, McGraw-Hill



               Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                         Rajkot                       3
Outline
   File Systems,
   Database Management,
   Motivation,
   Distributed Computing,& What is distributed,
   What is a Distributed Database System?
   What is not a DDBS?
   Centralized DBMS on a Network
   Distributed DBMS Environment
   Implicit Assumptions
   Shared-Memory Architecture, Shared-Disk
    Architecture, Shared-Nothing Architecture
   Applications,

                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       4
Outline
   Distributed DBMS Promises of DDBS
   Transparent Management of Distributed and
    Replicated data, Transparencies
   Distributed Database – User View
   Distributed DBMS – Reality, Potentially
    Improved Performance,
   Complicating Factors, Problem Areas,
    Parallelism Requirements, System Expansion
   Distributed DBMS Issues, Distributed DBMS
    Issues, Relationship Between Issues
                Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                          Rajkot                       5
Slide reference

 Most of the slides are taken from the following
  link
http://softbase.uwaterloo.ca/~tozsu/ddbook/notes/




                Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                          Rajkot                       6
Introduction
   Distributed Database System (DDBS)
    technology is the union of what appear to be
    two diametrically opposed approaches to
    data processing :
        Database System
        Computer Network




                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       7
Traditional File Processing System




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       8
    Database System

     The main aim is
     Data is defined and
      administered
      centrally
     Data independence




                      Prof. A.R. Vasant, V.V.P. Engineering College,
    11/30/2012                            Rajkot                       9
Motivation
   Major motivations behind the use of database
    systems is the desire to integrate the operational
    data of an enterprise and to provide centralized,
    thus controlled access to that data.
   The technology of computer networks, promotes a
    mode of work that goes against all centralization
    efforts.
   It seems difficult to understand how these two
    contrasting technology can possibly be
    synthesized to produce a technology that is
    more powerful and more promising than either
    one alone.

                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       10
Motivation
   The most important objective of Database
    technology is integration, not centralization
   It is possible to achieve integration without
    centralization, and that is what exactly the
    distributed database technology attempts
    to achieve
   Fundamental concepts and set the framework
    for distributed database concepts


                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       11
Motivation




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       12
Distributed Data Processing
   In the last couple of years,
        Distributed processing or Distributed computing
   Sometimes it was referred as
        Multiprocessor systems
        Distributed data processing
        Computer networks
   “Concept in search of a definition and a
    name”


                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       13
Distributed Data Processing
Synonymous terms
➠distributed function
➠distributed data processing
➠multiprocessors/multicomputers
➠satellite processing
➠backend processing
➠dedicated/special purpose computers
➠timeshared systems
➠functionally modular systems
              Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                        Rajkot                       14
Cont…

   Obviously, some degree of distributed
    processing goes on in any computer system,
    even on single-processor computers.
   CPU, I/O , ALU is separated, it can also be
    considered as distributed processing.
   But, we have nothing to do with a form of
    distribution of functions in a single-processor
    computer systems

                  Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                            Rajkot                       15
Distributed Data Processing Definiton

   A number of autonomous processing
    elements (not necessarily homogeneous)
    that are interconnected by a computer
    network and that cooperate in performing
    their assigned tasks

   Processing element refers to a computing
    device that can execute a program on its own

                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       16
What is being distributed?
   Processing logic
     Definition says processing logic or processing elements are
      distributed
   Function
     Distribution is according to function.
     Various functions of computer system could be delegated
      to various pieces of hardware or software.
   Data
     Distribution is according to data

     Data used by a number of applications may be distributed
      to a number of processing sites
   Control
     Control can be distributed
     Control of the execution of various tasks might be
      distributed instead of being performed by one computer
      system
                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       17
What is a Distributed Database System?

   A distributed database (DDB) is a collection of
    multiple, logically interrelated databases
    distributed over a computer network.

   A distributed database management system (D–
    DBMS) is the software that manages the DDB
    and provides an access mechanism that makes
    this distribution transparent to the users.

   Distributed database system (DDBS) = DDB + D–DBMS

                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       18
What is not a DDBS?
   A timesharing computer system
    A loosely (shared-disk) or tightly (shared-
    memory) coupled multiprocessor system
    A database system which resides at one of
    the nodes of a network of computers - this is
    a centralized database on a network node




                  Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                            Rajkot                       19
Shared Memory Architecture


         Processor             Processor                              Processor
            Unit                  Unit                                   Unit


                                 Memory



                           I/O System


                     Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                               Rajkot                                   20
Cont….
   A multiprocessor system is generally
    considered to be a system where two or more
    processors share some form of memory,
    either primary memory, in which case the
    multiprocessor is called shared memory (also
    called tightly coupled), or secondary memory,
    when it is called shared disk (also called
    loosely coupled).


                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       21
Shared Memory Architecture




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       22
Shared Disk Architecture




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       23
Cont….

   Shared everything and Shared nothing
    Architecture
   Shared everything permits each processor to
    access everything (Primary and secondary
    memories, and peripherals)
   Sharing memory enable processors to
    communicate without exchanging messages.


                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       24
Shared-Nothing Architecture




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       25
Cont….

   Shared nothing architecture is one where
    each processor has its own primary and
    secondary memory and peripherals, and
    communicates with other processors over a
    very high speed interconnect (bus or switch)
   In this manner it is similar to distributed
    environment but still there is a difference.



                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       26
Centralized DBMS on a Network




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       27
Distributed DBMS Environment

   It is obvious that the existence of a computer
    network or a collection of “files” is not
    sufficient to form a distributed databases
    system.
   What we are interested in is an environment
    where data is distributed among number of
    sites.



                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       28
Distributed DBMS Environment




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       29
Implicit Assumptions
 Data stored at a number of sites each site logically
  consists of a single processor.
 Processors at different sites are interconnected by
  a computer network (no multiprocessors)
➠parallel database systems
 Distributed database is a database, not a collection
  of files data logically related as exhibited in the
  users’ access patterns
➠relational data model
 D-DBMS is a full-fledged DBMS

➠not remote file system, not a TP system

                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       30
Applications

   Manufacturing - especially multi-plant
    manufacturing
   Military command and control
   Corporate MIS
   Airlines
   Hotel chains
   Any organization which has a decentralized
    organization structure
                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       31
Distributed DBMS Promises
❶Transparent management of distributed,
 fragmented, and replicated data
❷Improved reliability/availability through
 distributed transactions
❸Improved performance
❹Easier and more economical system
 expansion



               Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                         Rajkot                       32
Distributed DBMS Promises
   Higher reliability
   Replication of components
   No single points of failure
   e.g., a broken communication link or
    processing element does not bring down the
    entire system
   Distributed transaction processing
    guarantees the consistency of the database
    and concurrency
                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       33
Distributed DBMS Promises
   Improved performance
   Proximity of data to its points of use
        Reduces remote access delays
        Requires some support for fragmentation and replication
   Parallelism in execution
        Inter-query parallelism
        Intra-query parallelism
   Update and read-only queries influence the design
    of DDBSs substantially
        If mostly read-only access is required, as much as possible
         of the data should be replicated
        Writing becomes more complicated with replicated data

                         Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                   Rajkot                       34
Distributed DBMS Promises
   Easier system expansion
   Issue is database scaling
   Emergence of microprocessor and workstation
    technologies
        Network of workstations much cheaper than a
         single mainframe computer
   Data communication cost versus
    telecommunication cost
   Increasing database size

                     Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                               Rajkot                       35
Transparency
   Transparency is the separation of the higher-level semantics
    of a system from the lower-level implementation issues
   Transparent system hides the implementation details from
    users
   Ex. A firm that has offices at different locations
     Boston, Paris, Montreal, Newyork

     They run projects at each of these sites and would maintain
       a database of their employees, projects and other related
       data
     EMP(ENO, ENAME, TITLE)

     Proj (PNO,PNAME,BUDGET)

     PAY(TITLE,SAL)

     ASG(ENO,PNO,DUR,RESP)


                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       36
Cont….
   If it would have been centralized database
    and we wanted to find out the names of
    employees who worked on a project for more
    than 12 months, then SQL query
             SELECT ENAME, SAL
             FROM EMP,ASG,PAY
             WHERE ASG.DUR > 12
             AND EMP.ENO=ASG.ENO
             AND PAY.TITLE=EMP.TITLE


                    Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                              Rajkot                       37
Example




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       38
Cont….




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       39
Cont….
   We need to partition each of the relations and
    store each partition at a different site.
   This is known as fragmentation
   It is also preferable to duplicate some of this
    data at other sites for performance and
    reliability reasons
        Fragmented and replicated distributed database
   User can pose the query without paying
    attention to the fragmentation, location, or
    replication of data, let the system worry about
    resolving these issues.
                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       40
Transparency
   Fundamental issue is to provide
        data independence
    in the distributed environment
        Network (distribution) transparency
        Replication transparency
        Fragmentation transparency
            horizontal fragmentation: selection
            vertical fragmentation: projection
            hybrid



                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       41
Data Independence
   Fundamental form of transparency that we
    look within a DBMS, distributed or centralized
   It refers to the immunity of user applications
    to changes in the definition and organization
    of data and vice versa
   Later, we will see that
   Logical structure of data is called schema
    definition
   Physical structure of data is called physical
    data description
                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       42
Cont…
   Two types of data independence
        Logical data independence
        Physical data independence
   Logical data independence
            Refers to the immunity of user application to changes in
             the logical structure of the database.
                If a user application operates on a subset of the attributes
                 of a relation, it should not be affected later when new
                 attributes are added to the same relation
                  EMP relation (new attributes added then no change to
                     application program)


                             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                       Rajkot                         43
Cont…
   Physical data independence
        Hiding details of the storage structure from user
         applications.
        The data might e stored on different disk types,
         parts of it might be organized differently or might
         even be distributed so application program should
         not    be     concerned    with    physical    data
         independence
        Application program need be changed.



                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       44
Network Transparency
   The second resource need to be managed in
    distributed database environment is : The network
       User should be protected from the operational details of
        the network
       Desirable to hide even the existence of the network
       Users can view DDBS as centralized DBMS
   This type of transparency is referred to as network
    transparency or distributed transparency
       User can access services or data
       Users do not have to specify where data is located

                       Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                 Rajkot                       45
Cont….

   Distribution transparency
        Location transparency
            The command used to perform a task is independent of
             both the system on which the data is stored and the
             system on which the command is executed
        Naming transparency
            a unique name is provided for each object in the
             database. The name does not have object location
             associated with it.



                         Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                   Rajkot                       46
Replication Transparency
   In detail it will be discussed later
   Just for the performance, reliability and availability
    reasons, it is usually desirable to be able to
    distribute data in a replicated fashion across the
    machines on a network
   Ex
        Data required by one user can be placed on that user’s
         local machine as well as on the machine of another user
         also
            It increases locality of reference
            If one of the machine fails, a copy of the data is still available
             on another machine on the network.
                            Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                      Rajkot                       47
Cont…

   Whether to replicate or not?
   How many copies?
   How update operations will work?
   User should be aware or not?




                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       48
Fragmentation
   It is commonly desirable to divide each database
    relation into smaller fragments and treat each
    fragment as a separate database object (i.e.
    another relation)
   This is done for performance, availability and
    reliability
   Fragmentation can reduce the negative effect of
    replication
   Each replica is not a full relation but only a
    subset of it; thus less space is required and
    fewer data items need be managed

                  Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                            Rajkot                       49
Cont…
   Horizontal fragmentation
        Relation is partitioned into a subset of the tuples (rows)
   Vertical fragmentation
        Relation is partitioned into a subset of the attributes
         (columns)
   When the database objects are fragmented, the
    problem of handling user queries that were specified
    on entire relations now to be performed on sub-
    relations
   Finding query processing strategy based on
    fragmentation

                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       50
Assignment 1

   Explain file processing and DBMS
   What do you mean by Distributed data Processing?
   Explain shared memory architecture
   Explain shared Disk architecture
   Explain central database on a network
   Explain DDBS environment
   Give an example of Distributed application and
    explain
   Define Transparency and explain different types of
    transparencies in DDBS.

                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       51
Distributed Database - User View




      User wants to see one database
                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       52
Distributed DBMS - Reality




        Programmer sees many databases
                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       53
Who should provide transparency?
    Application
    The transparency features can be built into the user
     language, which then translates the requested
     services into required operations.
            Applications or application modules are implemented
             in a distributed fashion
            Communication and data exchange via standard
             protocols (RPC, CORBA, HTTP, . . . )




                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       54
Who should provide transparency?
   Operating system
     provides some level of transparency to system users.

   Example, the device drivers within the operating system
    handle the details of getting each piece of peripheral
    equipment to do what is requested.
   The typical computer user, or even an application
    programmer, does not normally write device drivers to
    interact with individual peripheral equipment; that
    operation is transparent to the user.
   In the distributed environment, where the management
    of the network resource is taken over by the distributed
    operating system
     Realizes network transparency, e.g., on file system
       level (NFS) or protocol level

                    Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                              Rajkot                       55
Who should provide transparency?
   Database system
   The third layer at which transparency can be supported
    is within the DBMS.
   It is the responsibility of the DBMS to make all the
    necessary translations from the operating system to the
    higher-level user interface
     Transparent access to data at remote database

        instances
     Requires splitting queries, transaction control,

        replication


                     Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                               Rajkot                       56
Layers of Transparency




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       57
Reliability Through Distributed Transactions
      Distributed DBMSs are intended to improve reliability
       since they have replicated components and, thereby
       eliminate single points of failure.
      Compensating node failures by data copies (replicates)
       on remote sites
      Distributed transactions guarantee that
1.     A sequence of database operations is executed as an
       atomic action
2.     A consistent database state is transformed to another
       consistent database state, even if multiple transactions
       are executed concurrently (concurrency transparency
       & failure atomicity)
                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       58
Reliability Through Distributed Transactions
   Example
   Assume that there is an application that updates the
    salaries of all the employees by 10%.
   It is desirable to encapsulate the query (or the program
    code) that accomplishes this task within transaction
    boundaries.
   For example, if a system failure occurs half-way through
    the execution of this program, we would like the DBMS to
    be able to determine, upon recovery, where it left off and
    continue with its operation (or start all over again). This is
    the topic of failure atomicity.


                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       59
Reliability Through Distributed Transactions
   Alternatively, if some other user runs a query
    calculating the average salaries of the employees in
    this firm while the original update action is going on,
    the calculated result will be in error.
   Therefore we would like the system to be able to
    synchronize the concurrent execution of these
    two programs.




                    Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                              Rajkot                       60
Improved Performance
   Fragmenting the conceptual database in a
    way that enables data to be stored in close
    proximity to its points of use
        reduction of transfer costs and delays
   Inherent parallelism of distributed systems
        Inter-query parallelism: execution of multiple
         queries at the same time
        Intra-query parallelism: parallel execution of sub
         queries at different sites accessing a different part
         of the distributed database

                       Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                 Rajkot                       61
Cont….
   Read-only vs. update access
     Query database (for ad-hoc querying) and production

      database (for updates by application programs)
       Copying the production database to the query
        database at regular time intervals
     Read-only access during regular operating hours,

      updates are batched and executed during off hours




                    Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                              Rajkot                       62
Easier system expansion
   Necessity of increasing database size and/or
    decreasing query execution time
   Expansion by adding additional storage and
    processing power to the network
   A system of smaller computers is often
    cheaper than a single big machine with the
    equivalent power



                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       63
Complicating Factors
      First, data may be replicated in a distributed
       environment
      The possible duplication of data items is mainly due to
       reliability and efficiency considerations.
      Consequently, the distributed database system is
       responsible for
(1)    choosing one of the stored copies of the requested
       data for access in case of retrievals, and
(2)    making sure that the effect of an update is reflected on
       each and every copy of that data item.



                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       64
Complicating Factors
   Second, if some sites fail (e.g., by either hardware or
    software malfunction), or
   if some communication links fail (making some of the
    sites unreachable) while an update is being executed,
   the system must make sure that the effects will be
    reflected on the data residing at the failing or
    unreachable sites as soon as the system can recover
    from the failure.

   The third point is the synchronization of transactions on
    multiple sites is considerably harder than for a centralized
    system.


                     Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                               Rajkot                       65
Complicating Factors
   These difficulties point to a number of potential problems
    with distributed DBMSs.
   Complexity
        DDBS are complex compare to centralized DBMS
   Cost
        DDBS requires additional hardware, communication mechanism
         etc which increases the cost.
        Software is also complicated and required for DDBS
        To maintain DDBS an increase in the personnel at different sites
   Distribution of Control
        Distribution creates the problem of synchronization and
         coordination that must be handled and policies to be defined

                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       66
Complicating Factors

   Security
        In centralized DBMS this was the major benefit
        How to maintain security in DDBS is the major factor, also
         network security is a major factor.




                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       67
Design Issues/ Problem Areas
   There are number of technical problems that
    need to be resolved to realize the full
    potential of DDBMS
   Distributed database design
        how to distribute the database?
        How to fragment the data?
        Partitioned data vs. replicated data?




                       Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                 Rajkot                       68
Design Issues/ Problem Areas
   Distributed query processing
        Design algorithms that analyze queries and
         convert them into a series of data manipulation
         operations
        Executing a query over the network in the most
         cost-effective way
        Distribution of data, communication costs, etc. has
         to be considered
        Find optimal query plans


                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       69
Design Issues/ Problem Areas
   Distributed directory management
       A directory contains information (such as
        descriptions and locations) about data items in the
        database.
       A directory may be
            global to the entire DDBS or local to each site;
            it can be centralized at one site or distributed over
             several sites;
            there can be a single copy or multiple copies.



                          Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                    Rajkot                       70
Design Issues/ Problem Areas

   Distributed concurrency control
        Synchronization of concurrent accesses such that
         the integrity of the DB is maintained
        Integrity of multiple copies of (parts of) the DB
         have to be considered (mutual consistency)
        Synchronizing access such that integrity is
         maintained




                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       71
Design Issues/ Problem Areas

   Distributed deadlock management
        Deadlock management: prevention, avoidance,
         detection/recovery
   Reliability of distributed DBMS
        Ensure consistency, detect failures, and recover
         from failures
        How to make the system resilient to failures
        Atomicity and durability


                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       72
Design Issues/ Problem Areas
   Operating System Support
        operating system with proper support for database
         operations
        dichotomy between general purpose processing
         requirements and database processing requirements
   Heterogeneous databases
        If there is no homogeneity among the DBs at various
         sites either in terms of the way data is logically
         structured (data model) or in terms of the access
         mechanisms (language), it becomes necessary to
         provide translation mechanisms

                      Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                                Rajkot                       73
Relationship Between Issues




             Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                       Rajkot                       74
Conclusion
   A distributed database (DDB) is a collection of
    multiple, logically interrelated databases distributed
    over a computer network
   Data stored at a number of sites, the sites are
    connected by a network. DDB supports the
    relational model. DDB is not a remote file system
   Transparent system ‘hides’ the implementation
    details from the users
     Distribution transparency

     Network transparency
     Transaction transparency

     Performance transparency



                    Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                              Rajkot                       75
Conclusion

   Programming a distributed database involves:
     Distributed database design

     Distributed query processing

     Distributed directory management

     Distributed concurrency control

     Distributed deadlock management

     Reliability




                   Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                             Rajkot                       76
Assignment 2
   Explain Layers of Transparency
   Discuss in detail the problem areas in DDBS
    environment
   How do you explain the improved performance
    in DDBS environment?
   Discuss the complicating factors in DDBS
    environment.
   Give the advantages and disadvantages of
    DDBS.


                 Prof. A.R. Vasant, V.V.P. Engineering College,
11/30/2012                           Rajkot                       77

				
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Description: Distributed Database System (DDBS) technology is the union of what appear to be two diametrically opposed approaches to data processing : Database System Computer Network