Relational Database Management Systems

What is a Database?

• A database is an organized collection of structured information or data, typically stored electronically in a computer system.
• A relational database is a type of database that uses a relational structure to identify and access data in relation to another piece of data in the database.
• Data in a relational database is often organized into tables.

Relational Database Management System (RDBMS)

• A Relational Database Management System (RDBMS) is a program that allows you to create, update, and administer a relational database.
• Most RDBMS use the SQL language to access the database.

Basic Terminologies and Concepts

• Table: A collection of related data
• Schema: The structure of a database
• Tuple/Record: A row in a table
• Attribute: A column in a table
• Cardinality: The number of tuples in a table
• Degree of Relation: The number of attributes in a table
• Field: A column in a table
• Entity: An object or concept that can be described with a set of attributes
• Keys: Primary and Foreign keys
• Queries: Requests for specific data from a database

Entity-Relationship Model

• The Entity-Relationship Model is a model for identifying entities to be represented in the database and representing how those entities are related.
• ER diagrams are used to visualize the relationships between entities.

Components of ER Diagram

• Strong and Weak Entity
• Key Attributes
• Composite Attributes
• Multivalued Attributes
• Derived Attributes
• Relationships: One to One, One to Many, Many to One, Many to Many

Notation for Relationship in ER Diagram

• Using Crow's Foot Notation

Steps to Draw ER Diagram

• Identify all the entities
• Identify the relationship between the entities
• Find the attributes of each entity
• Remove redundant entities and attributes

Converting ER Diagram to Relational Schema

• Draw the ER diagram and convert it into relational schema

Business Rules

• Business rules are used to describe the properties of an application
• A business rule can be:
  • A description of a concept relevant to the application
  • An integrity constraint on the data of the application
  • A derivation rule, where information can be derived from other information within a schema

Symbols Used in ER Models

• Entity: Represents the entities
• Attribute: Represents the attributes
• Relationship: Represents the type of relationship between the entities
• Weak Entity: Represents a weak entity
• Multivalued Attribute: Represents multivalued attributes
• Derived Attribute: Represents derived attributes