GATE CSE 1990 Question 2-iv: Database Concepts Explained | Digiimento
A comprehensive guide to understanding key database concepts for GATE aspirants
Original GATE Question
Year: 1990
Question Number: 2-iv
Instructions: Match the following database concepts with their corresponding terms:
- Secondary index – (q) B-tree
- Non-procedural query language – (r) Domain calculus
- Closure of a set of attributes – (p) Function dependency
- Natural join – (s) Relational algebraic operations
Detailed Solution
Let’s break down each pairing and explain why they are correct:
a. Secondary index – (q) B-tree
A secondary index is a database index structure that improves the speed of data retrieval operations. B-trees are commonly used to implement secondary indexes due to their efficiency in search, insertion, and deletion operations.
- B-tree characteristics: Balanced tree structure, efficient for range queries, and maintains sorted data.
- Advantages for indexing: Logarithmic time complexity for operations, minimizes disk I/O, and supports both equality and range queries.
b. Non-procedural query language – (r) Domain calculus
Domain calculus is a type of non-procedural query language used in relational database theory. It allows users to specify what data they want without detailing how to retrieve it.
- Non-procedural nature: Users declare the desired result without specifying the sequence of operations.
- Domain variables: Operates on domains (sets of values) rather than on tuples.
- Example: {x | ∃t ∈ R (t[A] = x ∧ t[B] > 100)} – This query retrieves all values of attribute A where the corresponding B value is greater than 100.
c. Closure of a set of attributes – (p) Function dependency
The closure of a set of attributes is closely related to functional dependencies in relational database theory. It helps in determining the set of all attributes that are functionally determined by a given set of attributes.
- Functional Dependency (FD): A constraint between two sets of attributes in a relation.
- Closure: The set of all attributes that can be determined from a given set of attributes using the available functional dependencies.
- Example: If we have FDs A → B and B → C, then the closure of {A} would be {A, B, C}.
d. Natural join – (s) Relational algebraic operations
Natural join is a fundamental operation in relational algebra, which is used to combine relations (tables) based on their common attributes.
- Relational Algebra: A set of operations used to manipulate relations in a database.
- Natural Join: Combines two relations based on all their common attributes, eliminating duplicate columns.
- Example: R ⋈ S, where R and S are relations, combines tuples from R and S that have the same values for their common attributes.
Solution Summary
This GATE CSE 1990 question tests understanding of key database concepts:
- B-trees are efficient data structures used for implementing secondary indexes in databases.
- Domain calculus is a non-procedural query language that operates on domains of attributes.
- The closure of a set of attributes is determined by functional dependencies in a relation.
- Natural join is a relational algebraic operation that combines relations based on common attributes.
Understanding these concepts is crucial for database design, optimization, and query processing.
Frequently Asked Questions (FAQs)
1. Why are B-trees preferred for database indexing?
B-trees are preferred because they:
- Maintain balance, ensuring consistent performance
- Minimize disk I/O operations
- Support efficient range queries
- Allow for fast insertions and deletions
2. How does domain calculus differ from relational algebra?
While both are used for querying databases:
- Domain calculus is declarative, specifying what to retrieve
- Relational algebra is procedural, defining how to retrieve data
- Domain calculus uses logical expressions, relational algebra uses algebraic operations
3. What is the importance of functional dependencies in database design?
Functional dependencies are crucial for:
- Normalizing database schemas
- Eliminating data redundancy
- Ensuring data integrity
- Optimizing query processing
4. Can you explain the difference between natural join and other types of joins?
Natural join differs from other joins in that:
- It automatically uses all common attributes between relations
- It doesn’t require explicit join conditions
- It eliminates duplicate columns in the result
- Other joins (e.g., inner join, left join) may require specific conditions and can retain all columns
Additional Study Resources
To deepen your understanding of these database concepts, consider exploring the following topics: