Computer Science - IT MCQs
Topic Notes: Computer Science - IT
<p>MCQs and preparation resources for competitive exams, covering important concepts, past papers, and detailed explanations.</p>
Plato
- Biography: Ancient Greek philosopher (427–347 BCE), student of Socrates and teacher of Aristotle, founder of the Academy in Athens.
- Important Ideas:
- Theory of Forms
- Philosopher-King
- Ideal State
411
In a foreign key constraint, the `ON DELETE CASCADE` action specifies that:
Answer:
When a parent record is deleted, all corresponding child records should also be deleted.
`ON DELETE CASCADE` is a referential action that automatically deletes all matching records in the child table when a record in the parent table is deleted. This helps maintain referential integrity automatically.
412
The 'Entity Integrity' constraint states that:
Answer:
A primary key value cannot be NULL.
The entity integrity rule is a fundamental constraint of the relational model. It specifies that no attribute participating in the primary key of a table is allowed to have a NULL value.
413
A 'domain' in the relational model refers to:
Answer:
A set of permissible values for an attribute.
The domain of an attribute is the set of all unique, atomic values that the attribute can validly contain. For example, the domain for a 'Gender' attribute might be {'Male', 'Female', 'Other'}.
414
Which of the following contains information about the structure of a database?
Answer:
Data dictionary
A data dictionary, or metadata repository, contains information about the database's structure, including tables, columns, data types, and constraints.
415
What term is used for a collection of information to build reports or analyze data in an environment?
Answer:
Database
A database is a structured collection of data that can be analyzed and used for reporting.
416
The 'data dictionary' or 'system catalog' stores what type of information?
Answer:
Metadata
The data dictionary is a component of the DBMS that stores metadata. This includes information about schemas, tables, columns, data types, constraints, user permissions, and other structural information about the database.
417
What is a superkey?
Answer:
A set of attributes that can uniquely identify a tuple.
A superkey is a set of one or more attributes that, when taken together, can uniquely identify a record in a table. A candidate key is a minimal superkey, meaning it's a superkey from which no attributes can be removed without losing the uniqueness property.
418
Which aggregate function returns the total number of rows that match a specified criterion?
Answer:
COUNT()
The `COUNT()` function returns the number of rows. `COUNT(*)` returns the total number of rows in a table, while `COUNT(column)` returns the number of non-NULL values in that column.
419
Which of the following challenges is commonly associated with traditional file management systems, making them less efficient and robust than modern database management systems?
Answer:
Inability to perform complex queries across multiple data sets.
Traditional file management systems often store data in separate, application-specific files. This approach leads to several problems. While 'Program dependence' and 'Data redundancy' are valid issues, the option 'Inability to perform complex queries across multiple data sets' encapsulates a significant limitation. File systems are typically designed for basic record access rather than sophisticated querying and aggregation across disparate files. Options B, C, and D describe advantages typically found in modern database management systems, not problems in file management systems. For instance, file systems generally suffer from *lack* of data independence, *high* data redundancy, and *poor* data integrity compared to DBMS.
420
Which level of data abstraction describes *how* the data is actually stored?
Answer:
Physical level
The physical level is the lowest level of data abstraction. It describes the complex low-level data structures in detail, defining how the data is stored on physical storage devices like disks.