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      _________________  .____     ___________________
     /   _____/\_____  \ |    |    \_   _____/\______ \
     \_____  \  /  / \  \|    |     |    __)_  |    |  \
     /        \/   \_/.  \    |___  |        \ |    `   \
    /_______  /\_____\ \_/_______ \/_______  //_______  /
            \/        \__>       \/        \/         \/
    
    
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    . |02.02 - Data Dictionary                           .
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      The database  structure from user's  layer provides
    database  schema.  Database  schema  specifies  inner
    structure organization, semantics and constraints for
    data  access. Entity-Relatioin  (E-R) model  provides
    description  of   database  schema   structure.  It's
    constructed  of the  basic elements  called entities.
    And it show the relation between it.
    
      Entity is  the image  of thing  or object  from the
    real  world  distinct  from  other  object.  Entities
    are  described  in  the  database  by  specification.
    Entity  specification  includes  it's  character  and
    set  of   attributes  expressing   their  attributes.
    Relation express relationship between entities. Basic
    principle of  data extraction from  database consists
    of  search for  given  relation. If  it  is too  much
    information in the relation  it's common to implement
    mechanism to speed  the access to it. In  the case of
    relation  databases the  principle is  implemented on
    the physical layer by index usage.
    
      Database schema is set  of definitions given in the
    a definition language. The  result of the commands in
    the data definition language is te set of information
    stored in  special file called data  dictionary. Data
    dictionary includes  metadata. That can  be described
    as information  on data stored in  the database. Data
    dictionary  is  used  by  DBMS  (Database  Management
    System) before it will  start to manipulate or define
    database structure.  Data manipulation is the  set of
    transaction including  selecting, inserting, deleting
    or  updating of  the information  stored in  the data
    base. Data  manipulation Language allows  user access
    and  data manipulation  corresponding  to it's  inner
    structure.
    
    
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