How is data indexing implemented within a database management system and how does it affect query execution?

Indexing in a DBMS creates special data structures (such as B-trees or hash tables) that speed up data search and sorting. When executing a query, the DBMS uses the index to quickly find the needed records without scanning the entire table. This significantly improves query performance, especially with large volumes of data. However, indexes occupy additional space and slow down insert and update operations.