Adatfüggetlenség

Adatfüggetlenség, often translated as data independence, is a fundamental concept in database systems that refers to the ability to modify the database schema at one level without affecting the schema at a higher level. This separation of concerns is typically achieved through a multi-level schema architecture.

There are generally three levels of schemas: the external schema (or view level), the conceptual schema (or logical level), and the internal schema (or physical level). The external schema describes how individual users or applications perceive the data. The conceptual schema provides a global, integrated view of the entire database, describing all the entities, attributes, and relationships. The internal schema describes the physical storage structure of the data, including file organization, indexing, and data compression.

Data independence allows for changes to be made to the internal schema (e.g., changing storage structures, adding indexes) without requiring any modifications to the conceptual or external schemas. This is known as physical data independence. Similarly, changes to the conceptual schema (e.g., adding new attributes, restructuring relationships) can be made without affecting the external schemas, provided the external schemas can be adjusted to accommodate these changes. This is called logical data independence.

The primary benefit of data independence is increased flexibility and maintainability of the database system. It allows database administrators to evolve the physical storage without impacting users and enables application programmers to work with a stable logical view of the data even as the underlying implementation changes. This separation simplifies database development and maintenance by reducing the ripple effect of schema modifications across different layers of the system.