Latest update on Thursday 16 October 2008 à 09:43 by Jean-François Pillou.
ANSI/SPARC 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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