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    . |02.01 - DBMS and Database Layers                  .
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      Previously it was shown  where the database systems
    came from. In the beginning there was need to process
    natural language  questions and get  natural language
    answers from computers.
    
      On  the basis  of Deduction  Systems the  Data-base
    systems  were   built  by  separating   data  storage
    implementation from data processing algorithms.
    
      We  will  now try  to  show  some basic  terms  and
    principles needed for databases understanding.
    
      In the core of the  standard database is a Database
    Management  System (DBMS).  It's  designed to  manage
    data  sentences  and  it's   capable  to  handle  the
    database  growth  and  it's  structure  change.  DBMS
    enables  data structure  specification.  It takes  in
    account the  type of stored information.  It provides
    mechanism for data manipulation.
    
      If  there's need  to share  information among  many
    users  it's  task is  to  avoid  anomalies caused  by
    concurrent  access by  many users  to the  same data.
    Database System enables abstract  view on the data by
    giving abstract layer above the data storage and data
    management details.  Data in data base  can be stored
    in  complex data  structures. But  yet DBMS  provides
    effective interface for stored data access.
    
      Typical database model provides 3 main views on the
    stored data. It can be  sorted from the lowest to the
    highest  from  the  abstraction point  of  view.  The
    levels can be called physical, logical and user's. On
    the  lowest  level  of abstraction,  physical  level,
    there is description  on how the data  are stored and
    there  are  details on  the  data  structure. In  the
    middle layer, logical level,  there is described what
    data are stored and what's  the relation among it. In
    the highest level of  abstraction, user's level view,
    the users  access is allowed and  provides user's own
    view to  the data.  Application program is  a program
    using access to the  database and sometimes is placed
    in it's own application layer.
    
    
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