dequeue(): The operation to remove and return the element from the front of the queue. In Python, this can be implemented using list.pop(0) (though more efficient implementations exist using collections.deque).

peek() (or front()): An operation to view the front element of the queue without removing it.

isEmpty(): An operation to check if the queue contains any elements.

Applications: Printer job scheduling, CPU task scheduling, breadth-first search (BFS) algorithm.

4. Database Concepts

Introduction to Databases

Database: An organized collection of structured information, or data, typically stored electronically in a computer system. It is designed to efficiently store, retrieve, and manage large amounts of data.
DBMS (Database Management System): Software that allows users to define, create, maintain, and control access to the database. It acts as an interface between the database and its end-users or applications. Examples: MySQL, PostgreSQL, Oracle, SQL Server.
RDBMS (Relational Database Management System): A type of DBMS that organizes data into one or more tables (relations) of rows and columns. Data is structured in a way that allows it to be easily accessed and reassembled in many different ways without reorganizing the database tables.
Table (Relation): A collection of related data entries organized in terms of rows and columns. Each table represents a specific entity (e.g., 'Students', 'Courses').
Row (Tuple/Record): A single entry or instance within a table, representing a complete set of related data for a particular entity.
Column (Attribute/Field): A vertical entity in a table that contains all information associated with a specific attribute of the table's entity. E.g., 'Student_ID', 'Name', 'Age'.
Schema: The logical design or structure of a database, describing how the data is organized, including table names, column names, data types, and relationships between tables.
Instance: The actual data stored in a database at a particular moment in time.

Keys

Primary Key: A column or a set of columns in a table that uniquely identifies each row (record) in that table. A primary key must contain unique values and cannot contain NULL values. There can be only one primary key per table.
Candidate Key: A column or a set of columns that can uniquely identify each row in a table. A table can have multiple candidate keys. A primary key is chosen from the set of candidate keys.
Alternate Key: Any candidate key that is not chosen to be the primary key for a table.
Foreign Key: A column or a set of columns in one table (the referencing table) that refers to the primary key of another table (the referenced table). It establishes a link or relationship between two tables. It can contain duplicate values and NULL values.
Super Key: A set of one or more attributes that, taken collectively, can uniquely identify a tuple (row) in a relation (table). A candidate key is a minimal super key (i.e., no proper subset of its attributes is a super key).

Relational Algebra

Relational Algebra: A procedural query language that takes instances of relations as input and yields instances of relations as output. It uses a set of fundamental operations to manipulate relations.
Selection ($\sigma$): A unary operation that selects a subset of rows (tuples) from a relation that satisfy a specified condition. Notation: $\sigma_{condition}(R)$.
Projection ($\pi$): A unary operation that selects a subset of columns (attributes) from a relat