Data levels


The ANSI/SPARC architecture, which dates from 1975, defines abstraction levels for a database management system:

  • Internal (or physical) level: defines how data is stored, and how it is accessed.
  • Conceptual level: also called the DRM (data relationship model) or LDM (logical data model). It defines how information is arranged within the database.
  • External level: defines user views.

Characteristics of a DBMS

The three-level architecture defined by the ANSI/SPARC model keeps data and processing separate. Generally speaking, a DBMS must have the following characteristics:

  • Physical independence: The physical level may be modified independently of the conceptual level. This means that the user cannot see all the hardware components of the database, which is simply a transparent structure for representing the stored information.
  • Logical independence: The conceptual level must be editable without disrupting the physical level. In other words, the database's administrator must be able to make improvements without affecting the users' experience.
  • Ease of use: People who are not familiar with the database must be able to describe their query without referencing the database's technical components.
  • Speedy access: The system must be able to reply to queries as quickly as possible. This requires fast search algorithms.
  • Centralised administration: The DBMS must enable the administrator to manipulate data, add elements, and verify their integrity in a centralised manner.
  • Limiting redundancy: The DBMS must be able to avoid redundant information whenever possible, both to minimise errors and to prevent wasting memory.
  • Integrity verification: The data must be internally coherent, and when some elements reference other elements, the latter must be present.
  • Data sharing: The DBMS must allow for multiple users to simultaneously access to the database.
  • Data security: The DBMS must be capable of managing each user's data access rights.
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