Computer networks (or computer network, or simply network) indicates a set of autonomous computers connected by a single technology.
Two computers are said to be connected when they are able to exchange information.
Internet It is the most famous example of computer networks, in fact it is a network that connects all the computers in the world..
A host It is any device connected to a network.
Database
A fundamental element in networks are the database.
A database is a structured set of information (or data) usually stored electronically in a computer system.
Databases are essential to the Internet because they allow you to reliably store, organize, and quickly retrieve huge amounts of data: user profiles, posts, products, payments, messages, reservations, logs, permissions.
The database is controlled by software DBMS, Database Management System (database management system).
Data within databases is generally presented in rows and columns contained in a series of tables.
A table is made up of fields, the columns, and record, the lines.
A field is an attribute of data, whereas a record is a specific piece of data.
When you enter data, you insert a record into the table.
Example
Below is a student table where:
A query It is a user request that requests a specific set of records from the database using selection criteria.
Example
A query could be, for example, to fetch all student records that have the class attribute value 3.
The data contained in the database can be easily viewed, managed, modified, updated, checked, added, deleted and organized.
Most databases use the language SQL, Structured Query Language, to write data to tables and run queries.
Example
Imagine having a bookstore management application where you need to keep track of books, authors, and customers. In this case, a database could be used to organize and store all the relevant information.
Database structure:
Example of use:
Suppose a new customer, Marco, registers at the bookstore and wants to borrow J.R.R. Tolkien's "The Lord of the Rings." Here's how the application would use the database:
The application checks whether the book “The Lord of the Rings” is available by checking the available quantity in the “Books” table.
After confirming that the book is available, the application creates a new record in the “Loans” table with Marco’s information, the book, and the loan date.
The available quantity of the book is updated by subtracting one, since a copy has been borrowed.
If Marco returns the book by the expected return date, the application updates the record in the “Loans” table with the actual return date.
Meanwhile, if the application receives new books to catalog, they will be inserted into the “Books” table and the corresponding authors into the “Authors” table.
If a customer forgets to return a book by the due date, the app can set a notification to remind the customer to return the book on time.
The application can generate reports using database information, such as displaying which books are currently on loan, which books are most popular based on loans, a list of authors in the library, and so on.
In this example, the database plays a key role in organizing and managing information about the bookstore's books, authors, and customers, simplifying the process of borrowing and returning books, and providing tools for analyzing data about the bookstore's business.
Packet
The data that circulates on the network has a format called packet.
The packet is divided into two sections:
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