Database concepts Quiz Class 12

✅ Answer: (a) A structured collection of data

A database is a structured collection of data, organized so it can be efficiently stored, accessed, managed, and updated — much more than just a loose folder of files.

✅ Answer: (d) To centralize and organize data

Databases exist to centralize and organize data — bringing scattered information into one well-structured system that’s easy to search, update, and keep consistent, rather than spread across disconnected files.

✅ Answer: (c) To manage and organize data in a database

A DBMS is the software layer that lets users and applications create, manage, query, and organize data stored in a database — examples include MySQL, Oracle, and PostgreSQL.

✅ Answer: (b) The accuracy and consistency of data

Data integrity refers to keeping data accurate and consistent throughout its lifecycle — ensuring, for example, that a value in one table correctly matches related data elsewhere, with no contradictions or corruption.

✅ Answer: (a) It uses a table-based structure to organize data

A relational database organizes data into structured tables (rows and columns), with defined relationships between them — a far more organized and query-friendly approach than loose, unstructured files.

✅ Answer: (d) A table that stores data

In relational database terminology, a relation is simply the formal term for a table — a structured collection of rows (tuples) and columns (attributes).

✅ Answer: (b) A column or field in a table

An attribute is a column (field) in a table — representing one specific property of the data, like “Name” or “Age” in a Students table.

✅ Answer: (b) A row or record in a table

A tuple is a single row (record) in a table — representing one complete entry, like one specific student’s full set of details.

✅ Answer: (a) The set of allowed values for an attribute

A domain is the set of all permissible values an attribute can take — e.g. the domain for a “Gender” column might be restricted to just “M” or “F”.

✅ Answer: (b) The number of attributes in a relation

The degree of a relation is simply the number of columns (attributes) it has — e.g. a table with 5 columns has a degree of 5.

✅ Answer: (d) The number of tuples in a relation

Cardinality is the number of rows (tuples) a relation contains — e.g. a table with 100 records has a cardinality of 100.

✅ Answer: (c) An attribute (or set of attributes) that COULD uniquely identify each tuple in a table

A candidate key is any attribute (or combination) capable of uniquely identifying every row — a table can have multiple candidate keys, each a valid “candidate” for becoming the table’s primary key.

✅ Answer: (a) The candidate key that is specifically CHOSEN to be the main unique identifier for a table

A primary key is the one candidate key selected by the database designer to serve as the table’s official unique identifier. (This question is corrected from a version whose definition — “a unique identifier for a tuple” — was identical, word for word, to the definition given for “candidate key”, making the two concepts indistinguishable. The real distinction is that a table can have several candidate keys, but only one of them is chosen as the primary key.)

✅ Answer: (c) A candidate key that is NOT selected as the primary key

An alternate key is simply any candidate key that wasn’t chosen to be the primary key — it could still uniquely identify rows, but the primary key role went to a different candidate instead.

✅ Answer: (d) A field that links to the primary key in another table

A foreign key is an attribute in one table that references the primary key of another table — this is exactly how relational databases establish relationships between different tables.

✅ Answer: (b) Yes — a table may have several candidate keys, but the designer selects only ONE of them to serve as the primary key

This is exactly right: a table can have multiple candidate keys (each independently capable of uniquely identifying rows), but the designer picks just one to be the primary key — the rest become alternate keys.

✅ Answer: (b) No — a primary key must always have a value for every row, and cannot be NULL

A core rule of the relational model is that a primary key can never be NULL — since its whole job is to uniquely identify every row, allowing it to be empty would break that guarantee.

✅ Answer: (b) Degree = 6, Cardinality = 40

Degree counts the columns (attributes) — there are 6. Cardinality counts the rows (tuples) — there are 40. So Degree = 6, Cardinality = 40.

✅ Answer: (b) To maintain referential integrity by linking related records between two tables

A foreign key’s main job is to maintain referential integrity — ensuring that a value in one table (like a “StudentID” in a Marks table) actually corresponds to a real, existing record in the table it references (the Students table), preventing orphaned or inconsistent data.

✅ Answer: (b) It reduces data redundancy and helps maintain consistency across related data

One of the biggest advantages of a DBMS is reducing data redundancy (avoiding the same information being duplicated inconsistently in multiple places) and maintaining consistency, since related data is properly linked through keys rather than copy-pasted everywhere.