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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.
