This lesson introduces some fundamental concepts of computer networks: databases and packets in networks.
After defining what a computer network, the Internet, and a host are, the text explains the role of databases in online services: storing, organizing, and retrieving information such as profiles, messages, products, or school data.
The lesson then introduces the DBMS, relational databases, tables, fields, records, and queries, showing how data can be linked through common IDs.
In the final section, the concept of a packet is introduced: the unit of data transmitted over a network, consisting of a header and a payload.
Network Fundamentals
A computer network—also called a data network or simply a network—is a group of autonomous devices connected to one another and capable of exchanging data through shared technologies (Kurose & Ross, 2026; Tanenbaum et al., 2022).
Two computers are considered connected when they are able to exchange information.
The Internet is the best-known example of a computer network: it is a large global network connecting billions of hosts around the world (Kurose & Ross, 2026).
A host is any device connected to a network (Kurose & Ross, 2026).
Database
A network allows multiple devices to communicate and exchange information. However, many network services do more than simply transmit data from one device to another: they must also store, organise, and retrieve it when needed.
For example, a social network must store profiles, posts, and messages; an e-commerce website must manage products, users, orders, and payments; and a school platform must store information about students, teachers, grades, absences, and communications.
Databases are used to perform these functions.
A database is a collection of information, or data, organised in a structured way and generally stored electronically within a computer system (Hoffer et al., 2026).
Databases are essential to the Internet because they make it possible to store, organise, and quickly retrieve enormous amounts of data reliably, such as user profiles, posts, products, payments, messages, bookings, logs, and permissions.
A database is managed by software called a DBMS, an acronym for Database Management System. A DBMS makes it possible to insert, modify, delete, search, and organise data (Hoffer et al., 2026).
Most databases are relational databases (Hoffer et al., 2026).
Data in relational databases is generally organised into rows and columns contained in a series of tables (Hoffer et al., 2026).
A table consists of:
A record is a row in a table and represents a single stored item, such as a student.
A field is a column in a table and represents one of the characteristics of that item, such as first name, last name, or class.
When a new item is added to the table, a new record is inserted.
For example, adding a new student means creating a new row in the “Students” table.
Example
Below is a table containing student records, where:
| First name | Last name | Class |
|---|---|---|
| Mario | Rossi | 3 |
| Giuseppe | Bianchi | 3 |
| Luca | Verdi | 2 |
A query is a request sent to a database. It can be used to search for data, insert new data, modify existing data, or delete data.
Example
For example, a query could ask the database to display all the students in class 3A.
The main characteristic of relational databases is that tables can be connected to one another through common fields, such as an identification code or ID (Hoffer et al., 2026).
For example, a “Students” table can be connected to a “Classes” table through the class ID. This makes it possible to organise large amounts of data, avoid unnecessary duplication, and easily retrieve information through queries.
Many relational databases use SQL, which stands for Structured Query Language, a language used to create, modify, and query tables (Hoffer et al., 2026).
Example
Imagine an application used to manage a library, in which you need to keep track of books, authors, and customers. In this case, a database could be used to organise and store all the relevant information.
Database structure
Example of use
Suppose that a new customer named Marco registers with the library and wants to borrow The Lord of the Rings by J.R.R. Tolkien. The application would use the database in the following way:
In this example, the database plays a fundamental role in organising and managing information about the library’s books, authors, and customers. It simplifies the borrowing and returning process and provides tools for analysing data about the library’s activities
Network packet
Many network services use databases to store and retrieve information.
However, when this data needs to travel from one device to another—for example, from a server to our computer—it is not sent as a single block. Instead, it is divided into smaller units called packets (Kurose & Ross, 2026).
A packet is a small unit of data transmitted through a network. Each packet contains both technical information, which is necessary to deliver it to the correct destination, and the actual data being transmitted (Deering & Hinden, 2017; Kurose & Ross, 2026).
A packet is generally divided into two main sections:
Key points
The School Network
A school has 25 computers in its computer lab, 4 network printers, a server that stores educational materials, and several tablets used by teachers. All these devices can communicate with one another through the school network.
Answer the following questions:
Designing a Gym Database
A gym wants to create a system to manage its members. For each customer, it wants to store their first name, last name, email address, registration date, and membership type. It must also record the available classes and keep track of which classes each customer attends.
Design a possible database structure.
Querying the School Database
A school uses a table called Students, consisting of the following fields:
ID | First Name | Last Name | Class | Email
The database contains 800 students.
The school administration needs to perform the following operations:
For each operation:
You do not need to write SQL code: you only need to correctly describe what the query should do.
The Database of a Streaming Platform
A platform wants to store information about its users and the available movies.
Initially, the following single table is proposed:
Username | Email | Movie Title | Director | Year | Viewing Date
A user who watches one hundred movies therefore appears one hundred times in the table, and the information about the same movie is repeated for every user who has watched it.
Analyze the problem and propose a better solution.
From the Server to Your Computer
Open an online platform and request an image stored on its server. The image must then travel across the network to your computer.
Using the concepts from the course material, describe what happens to the data during transmission.
To create these materials, I used generative artificial intelligence tools to support the writing process, particularly to improve the wording and style of the text, reorganize content, refine phrasing, and speed up certain editorial tasks.
Since I work independently on the production of these materials, I try to automate all activities that can reasonably be automated, so that I can devote more time to research, design, and content development.
However, artificial intelligence does not determine the content of the work: the selection of topics, structure, ideas, interpretations, examples, and teaching approach are developed by me. AI is therefore used primarily as a tool to support production and formal revision, while authorship and responsibility for the design and development of the content remain mine.
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