When users create, alter, or drop tables or create or drop indexes, the dbms updates the system catalog automatically.?
Computers and Technology · High School · Mon Jan 18 2021
Answered on
Yes, when users perform operations such as creating, altering, or dropping tables, or creating or dropping indexes in a database management system (DBMS), the system catalog is automatically updated. The system catalog is a set of tables maintained by the DBMS that contains metadata about the database objects. Metadata refers to data about data, and in this context, it includes information about the structure of tables, the data types and constraints of columns, the identities and attributes of indexes, user permissions, and other settings related to the database.
Let's walk through what happens during each of these operations regarding the system catalog updates:
1. **Creating a Table**: When a new table is created, the DBMS registers this table in the system catalog by creating new entries that describe the table's structure (e.g., table name, column names, data types, primary keys, foreign keys, and any constraints on the table).
2. **Altering a Table**: When a table is altered (for example, by adding or removing columns, changing data types, or modifying constraints), the DBMS updates the corresponding entries in the system catalog to reflect these changes.
3. **Dropping a Table**: When a table is dropped (deleted), the DBMS removes the relevant entries for that table from the system catalog so that the database no longer retains information about the now-deleted table.
4. **Creating an Index**: When an index is created on a table, the DBMS adds entries to the system catalog with details about the index, such as its name, the columns it includes, and its unique attributes if it's a unique index.
5. **Dropping an Index**: When an index is dropped, the corresponding system catalog entries for that index are deleted.
By keeping the system catalog up to date, the DBMS ensures that it accurately reflects the current state of the database's schema and object structure, which is critical for the DBMS's operations, optimization, and consistency checks