URL (Uniform Resource Locator), as the name suggests, provides a way to locate a resource on the web, the hypertext system that operates over the internet. The first part of a URL identifies what protocol to use. The second part identifies the IP address or domain name where the resource is located.
The main purpose of URL is to define how information on an Internet Protocol (IP) computer network is identified or differentiated from other types of information. It also details how users can work with this data by providing its location and describing its format and size.
URLs are often categorized into four types:
- Protocol Relative URLs - These start with "//" i.e., they are protocol-specific which means that there is no need to specify the protocol.
- Protocol Independent URLs - These start with "http://" and use a common syntax for specifying files, directories and other resources on the World Wide Web (WWW).
- Absolute URLs - These contain complete details of the resource which is to be accessed including its protocol. This allows one computer to connect with another over the Internet by using its IP address.
- Relative URLs - They are used for accessing computers on a local network through their LAN IP addresses or DNS names. Computers outside the local network can only be accessed via their public IP addresses or DNS names. Thus, relative URLs provide location independence by abstracting away the complexities of a particular network.
URLs are mainly divided into two categories:
- Online URL - This is the Web address of a resource available online over an IP based network. It can be accessed using http or https protocol. Online URLs appear in the following format: :://?. The scheme refers to either http or https, and specifies that there will be no authority section, which means that it's going to use the hostname from the end of the URL for this section. To find out what a domain name is, refer to What is a Domain Name .
The authority section includes the username, password or any other required information needed to access a resource. It may also include sub-sections such as the port number which is separated from the hostname with a colon (:).
The path section, or directory path, identifies a particular file within a specified website. For example, http://example.com/aboutme corresponds to files aboutme.html and aboutme.pdf on example.com's root directory.
The query string is used for providing additional information that can be passed to a web server as parameters when accessing a page or document. In most cases, this parameter contains data in name-value pair format which makes it easy to construct even complex searches using just a few characters without making lots of requests to the server for each individual search requirement.
- Offline URL - This is a Uniform Resource Locator that can be used to access resources in an offline storage such as a database, document or email message which is saved on the user's computer drive. They are different from online URLs since they don't use http protocol for accessing data over the internet and therefore do not have any kind of authority section in them. In addition, they also do not contain query strings or directory paths.
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