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Three-schema architecture is an idea in relational database design that breaks a database down into three different categories according to its use and structure, and to the roles played by system administrators, designers and end users.
Developed in the 1970s, the three-schema architecture helps to evaluate a relational database from different vantage points. The first of the three levels is called the external level or user level. This is the view of the relational database that end users see, and it involves a high level of abstraction. The second level is the logical schema or conceptual level, where designers work. The third level is the physical schema or physical level, where programmers maintain a database on a hardware system. The three-schema architecture is generally attributed to the ANSI/SPARC group and is sometimes also called "ANSI/SPARC" architecture.
Part of the usage of the three-schema architecture is to look at how the design maintenance differs from the core system maintenance. For example, items dealing with database tables and queries belong in the conceptual or logical schema, where issues such as memory handling are looked at in the physical level. Some IT experts talk about the three-schema architecture in the context of changing levels without affecting other levels or in terms of data independence. In addition, the three-schema architecture also performs a breakdown of the core duties of database designers, network administrators or server maintenance teams.