URL (Uniform Resource Locator) is the so-called address of the desired resource on the internet that consists of multiple components/parts.

Let’s take a look at the following URL

https://admin:pass@a.b.web.com:888/users/index.php?q=bob&role=2#info

This URL consist of the following components:

1. Scheme https://
2. Authority admin:pass@
3. Host a.b.web.com
4. Port 888
5. Path users/index.php
6. Query q=bob&role=2
7. Hash #info

Scheme component

Alternative naming: Protocol
Required: Yes
Example: https://

The scheme specifies which application will be used by a web server (app on Windows/i0S/Android) to open a URL.

For example, opening a URL with the scheme mailto:// will open your webmail application.

• Common examples: https://, http:// , ftp://, mailto://, file://
• Custom app examples: facetime://, slack://, steam://
• Browser specific examples: about://, chrome://
• Additional browser examples: data://, javascript://

Authority component

Alternative naming: HTTP authentication, credentials, authorization
Required: No
Example: admin:pass@

Basic authorization to a web/app resource indicated by @ (at) sign.
Login admin is separated from password pass using : (colon) sign

In some cases, a password is optional (e.g. https://admin@example.com)

Host component

Alternative naming: Hostname
Required: Yes
Example: a.b.web.com

The Host consists of multiple domain names separated by . (dot) sign.
Domain name with level > 2 is called sub-domain

1. a - fourth-level domain (sub-domain)
2. b - third-level domain (sub-domain)
3. web - second-level domain (domain name)
4. com - top/first-level domain (TLD)

The host can be an IP address in IPv4 (e.g. 193.184.216.34)
or IPv6 (e.g. [2a00:1450:400e:80a::200e]) format

Port component

Required: Yes
Example: 888

Port component indicates which server we are referring to on the target host

The : (colon) sign indicates port component usage. 888 is the port number

The server can accept connections on multiple ports. E.g. port numbers 80 and 443 can be used by a single server:

• 80 - port number is used for basic web connection
• 443 - port number is used for secure (TLS/SSL) web connection

The port :443 or :80 is omitted when a web page has https:// or http:// scheme

Path component

Required: No
Example: /users/index.php

Usually, the Path component indicates a path to the target file on a server

• / - the root path/folder. Let's imagine it is called htdocs
• users - folder named users inside of htdocs folder
• /index.php - file named index.php inside of users folder

In some cases, the Path component can use a custom mapping/scheme/rewrite rule. The path segments can be linked to a function/method in different files on a server:

• /users/list - functionlist in users.php file.
  show list of all users
• /users/1/read - functionread with argument ID in users.php file.
  show info of user with ID = 1
• /users/images - functionusers in image-collection.php file.
  show images of all users

Query component

Alternative naming: Query string, Search string, Parameters
Required: No
Example: ?q=bob&role=2

The Query component always starts with a ? (question) sign.
It consists of key-value pairs. The value is assigned to a key using the = (equals) sign.
Key-value pairs are separated using & (ampersand) sign.

1. ? - a starting symbol that indicates the presence of the Query component
2. q - the first key
3. = - the sign, that assigns the first value to a first key
4. bob - the first value
5. & - the key and value pair separator
6. role - the second key
7. = - the sign, that assigns second value to a second key
8. 2 - the second value

Example of logic behind this query: get all users named bob with role ID 2

Hash component

Alternative naming: Anchor
Required: No
Example: #info

Usually used by client-side scripting language named Javascript
By default - the browser will focus an element with id after # (hash) sign.
In our case, the focus will be made on an element with ID info

• # - starting symbol that indicates the presence of Hash component
• info - the value of a Hash component

Example of logic behind this hash: show tab with basic info for found users

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