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The notion of a three-schema model was first introduced in 1975 by the ANSI/X3/SPARC three level architecture, which determined three levels to model data. [1]The three-schema approach, or three-schema concept, in software engineering is an approach to building information systems and systems information management that originated in the 1970s.
The database schema is the structure of a database described in a formal language supported typically by a relational database management system (RDBMS). The term " schema " refers to the organization of data as a blueprint of how the database is constructed (divided into database tables in the case of relational databases ).
The internal structure of the database should be unaffected by changes to the physical aspects of the storage: For example, a changeover to a new disk. The three levels are: External Level (User Views): A user's view of the database describes a part of the database that is relevant to a particular user. It excludes irrelevant data as well as ...
The SQL/Schemata, or Information and Definition Schemas, part of the SQL standard is defined by ISO/IEC 9075-11:2008. SQL/Schemata defines the information schema and definition schema , providing a common set of tools to make SQL databases and objects self-describing.
Physical schema is a term used in data management to describe how data is to be represented and stored (files, indices, et al.) in secondary storage using a particular database management system (DBMS) (e.g., Oracle RDBMS, Sybase SQL Server, etc.).
A database relation (e.g. a database table) is said to meet third normal form standards if all the attributes (e.g. database columns) are functionally dependent on solely a key, except the case of functional dependency whose right hand side is a prime attribute (an attribute which is strictly included into some key).
A database abstraction layer (DBAL [1] or DAL) is an application programming interface which unifies the communication between a computer application and databases such as SQL Server, IBM Db2, MySQL, PostgreSQL, Oracle or SQLite. Traditionally, all database vendors provide their own interface that is tailored to their products.
Uniface was developed on the principles of the American National Standards Institute, (ANSI), 3-schema architecture. First proposed in 1975, this was a standard approach to the building of database management systems consisting of 3 schema (or metamodels): Conceptual schema—definition of all the data items and relationships between them.