_________________  .____     ___________________
 /   _____/\_____  \ |    |    \_   _____/\______ \
 \_____  \  /  / \  \|    |     |    __)_  |    |  \
 /        \/   \_/.  \    |___  |        \ |    `   \
/_______  /\_____\ \_/_______ \/_______  //_______  /
        \/        \__>       \/        \/         \/

. |02.02 - Data Dictionary                           .

  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

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