B.Tech Database Management Systems CS-502 Unit 2

Questions and Answers

A tuple is a mapping from attributes to values of those attributes. (correct)

A tuple is a fixed set of values that cannot change.

A tuple serves as a synonym for a relational schema.

A tuple is a collection of attributes grouped by a domain.

A relation is a named set of tuples that share the same attributes. (correct)

A relation is an unordered set of attributes with unique names.

A relation consists of distinct values across all its attributes.

A relation is a structured query for retrieving data from the database.

Domain is a synonym for the relational schema of a database.

Domain is a specific data structure used for indexing relations.

Domain refers to the unique identifier for each tuple.

Domain represents a set of atomic values from which data can be drawn. (correct)

<p>The number of attributes present in the relation.</p> Signup and view all the answers

<p>Relations do not maintain any order among their tuples.</p> Signup and view all the answers

Study Notes

Domain: A named set of atomic values, indivisible from the database's perspective.
- Examples include:
  - SSN: 9-digit number
  - Name: String starting with an uppercase letter
  - GPA: Real number between 0.0 and 4.0
  - Sex: {female, male}
  - Dept_Code: {CMPS, MATH, ENGL, etc.}
Attribute: Role name associated with a value from a specific domain; denoted as Dom(A).
Tuple: A mapping of attributes to values, representing an entity or relationship (e.g., {Name → "Keerthy", Sex → Male, IQ → 786}).
Relation: A set of tuples with the same attributes, commonly referred to as a table.
Relational Schema: Structure description of a relation (e.g., R(A1, A2, ..., An)), indicating attributes and their domains.
Relational Database: Collection of relations that align with their specified schemas.

Ordering of Tuples: Relations are sets, so tuples have no inherent order; referencing specific tuples (e.g., 5th tuple) is meaningless.
Intension vs. Extension:
- Intension: Permanent schema of a relation that does not change over time.
- Extension: Set of tuples present in a relation at any moment; varies over time.

Naming Structure: Includes the name of the relation and its attributes.
Set of Integrity Constraints: Includes various rules like:
- Entity Integrity Rule: Ensures primary keys are unique and not null.
- Referential Integrity Rule: Maintains consistency between related tables.
- Domain constraints for data value limitations.

Relational Query Languages: Utilize relational algebra to execute user requests.
- Procedural Languages: Specify how to obtain results through a sequence of operations (e.g., retrieve student marks and compute CGPA).
- Non-Procedural Languages: Define what data is needed without specifying how to fetch it (e.g., SQL).

Types of SQL Statements:
- DML (Data Manipulation Language): Operations for manipulating data.
- DDL (Data Definition Language): Statements for defining and modifying database structure.
- DCL (Data Control Language): Permissions and security.
- TCL (Transaction Control Language): Manage transactions in databases.

Combining Selection and Projection: Often combined to filter and display specific data from one relation efficiently.
- Example for selection of U.S. Supreme Court justices born in Arizona before 1935 using a selection (σ) and projection (π) operation.
Union Operation: Merges tuples from two relations with the same schema; noted as R3 = R1 ∪ R2.

Equi-Join vs. Natural Join: Equi-joins match values from different relations based on a specified attribute, while natural joins do so automatically on common attributes.

SELECT (σ): Retrieves tuples that meet a specific condition.
PROJECT (π): Retrieves specified attributes, eliminating duplicates.
UNION (∪): Combines tuples from two relations, ensuring union compatibility.

TRC: Based on retrieving entire tuples that match given conditions.
DRC: Focuses on selecting specific attributes based on conditions, expressed as {< a1, a2, ..., an > | P(a1, a2, ..., an)}.

Bound Variables: Maintain meaning even if replaced (e.g., conditions using ‘For All’).
Free Variables: Change meaning if replaced (e.g., different tuple variable results in a different query).