The following diagram portrays the ANSI/X3/SPARC architecture in greater detail and explicitly relates the various levels to their manifestations in a relational database management system. Note the following points:
The higher level within the External level is represented by the SQL language for relational systems. The SQL language elements can be embedded within a client application, within a stored procedure, or presented to the database in the form of an ad hoc, interactive query made through a query manager like BTEQ or SQL Assistant or through a natural language SQL code generator application.
The lower level with the External level is represented by a relational view. Views not only mask the underlying database storage, but also the conceptual structure it supports, acting as a virtual tabular interface on the physical base tables.
Note that not all users communicate with the database through views: some, particularly administrative users, communicate with the database directly.
The Conceptual level of the architecture is represented by the relational database management system and the file system. The role of the file system is more nebulous than the diagram portrays and is actually intermediate between the Conceptual and Internal levels, but for purposes of this description of the architecture, it is regarded as a component of the Conceptual level.
The Internal level of the architecture is represented by the disk subsystem. Depending on the configuration, the Internal level could also include storage media such as tape and optical disk. From the perspective of the architecture, only the file system has direct access to the disk subsystem, and it must map data requests and responses in a manner appropriate to the level or component it communicates with.