Networks and Databases: Sharing and Storing Data

When you send a message, watch a video, pay for something online or check your marks on a school website, two invisible systems are working together. A network carries the data from one place to another, and a database stores the data in an organised way so that it can be found, changed and protected. Almost every modern service depends on both. This guide explains networks first, then databases, and finally shows how the two work together every time you use an app or a website. Technical words are explained as they appear.

1.Part One: Computer Networks

A computer network is a group of devices, such as computers, phones, printers and servers, that are connected so they can share data and resources. Networks let people share files and printers, send messages, use the same internet connection, and store information in one central place. Without networks, every computer would work alone.

2.Types of Network by Size

The internet is the largest WAN: a network of networks, connected all over the world. You can read more about it in our article What Is the Internet, Really?

3.The Parts of a Network

In most homes, the modem, router and wireless access point are combined in one box, which people usually call "the router". It is still helpful to know the three jobs separately.

Cables and wireless

Ethernet cables use copper wires and are common inside buildings. Fibre-optic cables send data as pulses of light through thin glass threads, and they can carry very large amounts of data over long distances. Wi-Fi sends data by radio waves, which is convenient but usually slower and less stable than a cable, and weaker through thick walls.

4.Network Layouts (Topologies)

A topology is the way the devices of a network are arranged and connected.

Most modern local networks use the star layout, with a switch or wireless access point at the centre.

5.Client-Server and Peer-to-Peer

In a client-server network, clients ask a central server for services, such as files, email or web pages. This makes it easy to manage security and backups in one place. Schools, companies and most websites work this way. In a peer-to-peer network, every device can share files directly with the others, with no central server. It is cheap and simple for a few computers, but it is harder to manage and protect when it grows.

6.Addresses and Names

For data to arrive at the right place, every device needs an address.

• IP address: a number that identifies a device on a network. A common form, IPv4, has four numbers from 0 to 255 separated by dots, such as 192.168.1.10. This example is from a range reserved for private home and office networks. A newer form, IPv6, is much longer, because the world was running out of IPv4 addresses.
• MAC address: a unique hardware identifier built into a network card.
• Domain name: a name that humans can remember, such as a website address, instead of a number.
• DNS (Domain Name System): the internet's "phone book", which translates a domain name into the IP address of the right server. When you type a web address, a DNS server finds the number for you.

7.How Data Travels: Packets and Protocols

Data is not sent as one large piece. It is divided into small units called packets. Each packet has a header (the destination and source addresses, and a number showing its order) and the payload (a part of the real data). The packets may travel by different routes through routers, and the receiving device puts them back in the correct order. This is like posting a long letter as several numbered envelopes: if one envelope is lost, only that one needs to be sent again.

For this to work, all devices must follow the same rules, called protocols. A protocol is an agreed set of rules for communication.

Encryption means scrambling data so that only the person with the right key can read it. When a web address starts with "https" and shows a padlock, the connection between your device and the site is encrypted.

8.Speed: Bandwidth, Bits and Latency

Bandwidth is the maximum amount of data that a connection can carry in a given time. It is measured in bits per second, such as megabits per second (Mbps). A bit is the smallest unit of data, and 8 bits make 1 byte. Files are usually measured in bytes, such as megabytes (MB), so you must convert before comparing.

Latency is the delay before data starts to arrive, measured in milliseconds (ms). Low latency matters for video calls and online games, even when bandwidth is high. A connection can have high bandwidth and still feel slow if the latency is high.

9.Keeping a Network Safe

• Change default passwords on your router and use a strong Wi-Fi password.
• Use modern Wi-Fi security, such as WPA2 or WPA3, which encrypts the Wi-Fi signal.
• Keep devices and routers updated, because updates repair security weaknesses.
• Use a firewall: a program or device that checks network traffic and blocks what is unsafe.
• Be careful on public Wi-Fi. Avoid banking or entering passwords on an open network, unless the connection is protected.
• Use a VPN (virtual private network) if you need to connect safely to a work or school network from outside.

Our article on cybersecurity basics explains threats such as phishing and malware, and good habits for passwords.

10.Basic Network Troubleshooting

When a connection fails, a calm step-by-step check solves most problems:

1. Check whether only your device is affected, or other devices too.
2. Check that Wi-Fi is turned on, or that the cable is plugged in firmly.
3. Restart the device, and if other devices are also affected, restart the router.
4. Move closer to the router, because walls and distance weaken Wi-Fi.
5. Check for a service message from your internet provider.
6. If the problem remains, contact your provider or a teacher or technician.

11.Part Two: Databases

A database is an organised collection of data, stored so that it can be searched, updated and protected easily. A database management system (DBMS) is the software that controls the database, for example by adding data, finding it and deciding who may see it. School records, bank accounts, hospital systems, online shops and library catalogues all use databases.

A spreadsheet (see our guide to spreadsheets and documents) is excellent for small lists and calculations. A database is better when data is large, many people use it at once, the data is linked in complex ways, or accuracy and security are critical.

12.Tables, Records, Fields and Keys

Most databases are relational: they store data in tables that are linked to each other.

Suppose a school stores the teacher of each class. If every student's record repeated the teacher's name, a change of teacher would need hundreds of edits, and mistakes would appear. A better design uses two tables, linked by a key.

Here StudentID and ClassID (in the second table) are primary keys, and ClassID in the Students table is a foreign key. Each teacher is stored once, and if the teacher of 8A changes, only one record needs editing. Avoiding repeated data like this is called reducing redundancy. This relationship, where one class has many students, is called a one-to-many relationship.

13.Keeping Data Correct

A database is only useful if the data is accurate. Designers use several tools:

• Data types: each field accepts a certain type, such as text, whole number, date or yes/no.
• Validation: rules that check data when it is entered, such as "marks must be between 0 and 100" or "an email address must contain @".
• Required fields: some fields, such as the primary key, cannot be left empty.
• Integrity rules: for example, a student cannot be assigned to a class that does not exist.

Validation checks that data is sensible, but it cannot check that it is true. A person can still type the wrong, but valid, number.

14.Asking Questions with SQL

SQL (Structured Query Language, often pronounced "S-Q-L" or "sequel") is the standard language for working with relational databases. A query is a question or instruction that you send to the database. Here is a small table, called Students, to practise with.

Notice how SQL reads almost like English: choose these fields, from this table, where this condition is true. SQL works with the same ideas as the spreadsheet functions you may know, such as AVERAGE and COUNT, but it can handle far more data and many linked tables.

15.Other Kinds of Database

Relational databases, such as MySQL, PostgreSQL and SQLite, are very common, but not the only kind. NoSQL databases store data in other forms, for example as flexible documents or as simple key-and-value pairs. They are often used when data does not fit neatly into tables or when a system must handle huge amounts of changing data. The right choice depends on the job: relational databases are excellent when data is structured and accuracy is critical, such as in banking and school records.

16.Networks and Databases Working Together

Every time you use a website or an app, networks and databases cooperate. Consider ordering a book from an online shop:

1. Your phone (the client) sends a request across the network, first to your router and then across the internet. DNS has already found the shop's server address.
2. The shop's web server receives your request, in packets, over a protocol such as HTTPS.
3. The server asks a database for the book's price, description and stock.
4. The database sends the data back to the server, which builds the page.
5. When you buy, the server writes a new record in the orders table and updates the stock.
6. The page travels back across the network to your phone.

Often the web server and the database are on computers in a data centre run by a cloud company. Our article on cloud computing explains how this works.

17.Protecting Data

Databases often hold personal information, such as names, addresses and payment details, so protecting them is a serious responsibility. Many countries have laws about how personal data must be collected, stored and shared.

• Access control: each user gets only the permissions needed for their job.
• Strong authentication: strong passwords and, where possible, a second step such as a code.
• Encryption: protects data while it travels and while it is stored.
• Backups: regular copies that allow recovery after a failure or attack.
• Safe input handling: websites must check what users type into forms, because attackers sometimes try to trick a database by typing instructions instead of normal data. Careful programmers validate input and use safe query methods to prevent this.
• Updates: installing security updates for the database software.

As a user, share personal data only when it is necessary, use different strong passwords for different services, and read what a service says it will do with your information. For more, see Digital Footprint and Online Privacy.

18.Common Misunderstandings

19.Three Practice Projects

1. Draw your home network. Draw the router and every device that connects to it, label which use Wi-Fi and which use cables, and name the topology you see.
2. Design a small database. Choose a topic, such as a library or a shop. Plan two tables, write the fields, choose a primary key for each, and mark the foreign key. You can build it in a spreadsheet using two sheets.
3. Practise SQL. Use a free online SQL practice website to write the three queries in this article on your own table, and then invent three more.

20.Your Networks and Databases Checklist

• I can name the types of network: PAN, LAN, WLAN, MAN and WAN.
• I know what a router, switch and modem do.
• I can explain IP addresses, DNS, packets and protocols in simple words.
• I can convert bits to bytes and calculate a download time.
• I know the difference between a table, a record, a field, a primary key and a foreign key.
• I can read and write simple SELECT queries with WHERE and ORDER BY.
• I can describe how a website uses a network and a database together.
• I follow good safety habits for passwords, updates and public Wi-Fi.

Key Terms

A Closing Thought

Networks move data, and databases keep it organised, so together they form the foundation of almost everything you do online. You do not need to be a technician to understand them. If you can picture packets travelling between a client and a server, and tables linked by keys, you already understand the main ideas. Try one of the practice projects, and the next time a page loads, think of the many steps behind it: a name found, a path chosen, a question asked of a database, and an answer sent back in a fraction of a second.