The Correct Answer and Explanation is:
a. true
The statement that a database can support many logical views is correct. This is a fundamental feature of modern relational database management systems (RDBMS) and is crucial for data security, simplicity, and flexibility.
A logical view, often just called a view, is a virtual table based on the result set of a stored query. It does not store data itself but rather presents data from one or more underlying base tables in a predefined way. Because views are essentially named queries, a single database can support thousands of them, each tailored for a specific purpose or user group.
The primary reasons for supporting many logical views include:
- Security and Access Control: Views are a powerful tool for implementing security. A database administrator can grant a user permission to access a view but not the underlying tables. This allows the administrator to expose only specific columns or rows of a table, hiding sensitive information. For example, an HR view might show employee names and departments but hide salary information from general users, while a separate payroll view would include that sensitive data for authorized personnel only.
- Simplicity: Databases can have complex schemas with numerous tables and intricate relationships. A view can simplify this complexity for end users or application developers by presenting the result of a complex join or calculation as a single, simple table. Users can then query this view without needing to understand the underlying table structure or write complicated SQL statements.
- Logical Data Independence: Views help to create an abstraction layer between users and the physical tables. If the structure of the underlying tables changes, for example, a table is split into two, the view can be modified to maintain its original structure. This means that applications or user queries that rely on the view do not need to be rewritten, providing a stable interface even as the database schema evolves.
