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Questions and Answers
What is the structure of a relational database?
What is the structure of a relational database?
A relational database consists of relations (tables) with attributes (columns) and tuples (rows).
What is a database schema?
What is a database schema?
The logical structure of the database.
What is a primary key?
What is a primary key?
A candidate key that uniquely identifies a tuple in a relation.
What are attributes in a relational model?
What are attributes in a relational model?
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The order of tuples in a relation is relevant.
The order of tuples in a relation is relevant.
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Which of the following statements about superkeys is true?
Which of the following statements about superkeys is true?
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What is a foreign key constraint?
What is a foreign key constraint?
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Relational algebra is a procedural language.
Relational algebra is a procedural language.
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Which of these is NOT a pure relational query language?
Which of these is NOT a pure relational query language?
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In a relation, an element is called a ______.
In a relation, an element is called a ______.
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What do the null values indicate in a relation?
What do the null values indicate in a relation?
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Study Notes
Introduction to Relational Model
- The relational model is a widely used database model that organizes data into relations (tables).
- Each relation consists of rows (tuples) and columns (attributes), representing data about entities and their relationships.
- The model emphasizes data integrity through constraints like keys and foreign keys.
Database Schema
- The database schema defines the logical structure of a database, describing the relationships between different tables and their attributes.
- It acts as a blueprint for creating and managing the database.
- A database instance represents a snapshot of the actual data stored in the database at a specific point in time.
Keys
- Keys are used to uniquely identify rows within a relation.
- A superkey is a set of attributes that can uniquely identify each row in a table.
- A candidate key is a minimal superkey, meaning it contains no extra attributes that are unnecessary for unique identification.
- The primary key is selected from the set of candidate keys and identifies a unique row in a table.
- A foreign key constraint ensures that the values in one table (referencing relation) match the values in another table (referenced relation), enforcing data integrity and relationships between tables.
Schema Diagrams
- Schema diagrams visually represent the relationships and constraints within a database schema.
- They show the different tables, their attributes, and the relationships between them using symbols like lines and arrows.
Relational Query Languages
- Query languages are used to retrieve and manipulate data from relational databases.
- Relational algebra is a procedural query language that uses operations to manipulate relations and retrieve specific data.
- Other query languages include the tuple and domain relational calculi, which are non-procedural and use predicates to describe the desired data.
Relational Algebra
- Consists of seven basic operations:
- Selection: filters rows in a relation based on a specific condition.
- Projection: creates a new relation with a subset of columns from an existing relation.
- Union: combines rows from two relations with the same columns.
- Intersection: finds rows that are common to two relations.
- Difference: finds rows that are in one relation but not in another.
- Cartesian Product: combines all possible pairs of rows from two relations.
- Join: combines rows from two relations based on a common attribute.
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Description
Explore the foundational concepts of the relational model in databases, including data organization into tables, schema definitions, and the critical role of keys. Understand how these elements contribute to data integrity and management.
