What Is a URI (Uniform Resource Identifier)?

Every URI follows a defined syntax, and no two URIs are exactly the same. Each one is made up of components like a scheme, authority, path, query, and fragment. Some URIs only name the resource, others tell the browser exactly where to find it. That difference is what splits URIs into two main types: URLs and URNs.

How Does a Uniform Resource Identifier Work?

Well, URI functions by specifying the name as well as the location of a digital entity. The browser reads the syntax and then fetches the data for a user. Some of the commonly used URI schemes are – http, https, and mailto. They aid in identifying how to reach the resources. You say that schemes serve as the bases on which URIs work across the web.

As you enter the URI, the browser will direct you to a specific web page or file. If you enter a correct URI, the system returns the data. The role of  references is to connect different files as well as components online or offline.

URI Syntax: 5 Parts of a URI

Every URI follows the same general structure defined by RFC 3986. A full URI is made of up to five components:

• Scheme: tells the browser what protocol to use (for example, https, mailto, ftp, file).
• Authority: usually a domain and optional port, like proxywing.com:443.
• Path: the location of the resource on the host, like /glossary/uri.
• Query: extra parameters after a ?, like ?id=42&lang=en.
• Fragment: a pointer to a section inside the resource, after a #, like #syntax.

Put together, a URI looks like this:

scheme://authority/path?query#fragment

A real example: https://proxywing.com/glossary/uri?ref=blog#examples. Not every URI uses every part. A simple mailto:info@proxywing.com only has a scheme and a path. The structure stays the same, the components just change depending on what kind of resource you are pointing to.

Types of URI: URL vs URN

URIs come in two main types.

• URL (Uniform Resource Locator). A URL is a URI that locates a resource. It tells the browser where to find it and how to reach it. Example: https://proxywing.com/glossary/uri. All URLs are URIs.
• URN (Uniform Resource Name). A URN is a URI that names a resource without saying where it lives. It is a permanent identifier that does not change even if the file moves. Example: urn:isbn:0451450523, this names a specific book by its ISBN, no matter which library or website hosts it.

All URLs are URIs, all URNs are URIs, but not all URIs are URLs. A URI is the umbrella term. URL answers where, URN answers what.

Common URI Schemes

The scheme is the first part of every URI and tells the system how to handle the resource. Here are the most common ones you will see across the web:

• http / https — standard web pages. Example: https://proxywing.com.
• mailto — opens an email client. Example: mailto:business@proxywing.com.
• ftp — file transfer over FTP. Example: ftp://files.example.com/report.zip.
• file — points to a file on the local machine. Example: file:///C:/Users/Admin/notes.txt.
• data — embeds the data directly inside the URI. Example: data:text/plain;base64,SGVsbG8=.
• tel — opens a phone dialer. Example: tel:+15551234567.
• urn — names a resource without locating it. Example: urn:isbn:0451450523.

Each scheme has its own rules for what comes after it. The IANA keeps the official list of registered URI schemes, and new ones get added over time as new protocols appear.

Pros & Cons

URIs are pretty easy to read and use. They are great for creating consistent links and paths. They support many URI schemes and, at the same time, handle many instances of files or services.

But URI syntax can get complex. Incorrect characters can break the URI or cause errors while researching on the web. Also, some URIs don’t work without the right file system or access rights.

URI Examples

Here are valid URIs across different schemes, each pointing to a different kind of resource:

• https://proxywing.com/about — a web page (URL, https scheme).
  mailto:business@proxywing.com — an email address (URL, mailto scheme).
• ftp://files.example.com/report.zip — a file on an FTP server (URL, ftp scheme).
• file:///C:/Users/Admin/notes.txt — a local file (URL, file scheme).
• tel:+15551234567 — a phone number (URL, tel scheme).
• urn:isbn:0451450523 — a book identified by ISBN (URN).
• urn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66 — a globally unique identifier (URN).

Notice the pattern: every URI starts with a scheme followed by a colon. After that, the syntax depends on what the scheme expects. If the syntax breaks or contains invalid characters, the URI becomes invalid and the resource will not be returned.

FAQs

What does URI stand for?

URI stands for Uniform Resource Identifier. It is a string of characters that identifies a resource on the web, such as a page, file, or email address.

What is the full form of URI?

The full form of URI is Uniform Resource Identifier. The term was defined in RFC 3986 by the Internet Engineering Task Force (IETF).

What is the difference between a URI and a URL?

A URL is a type of URI. A URI is the broader term, it identifies a resource. A URL is a URI that also tells you where to find that resource. All URLs are URIs, but not every URI is a URL.

What is a URI in networking?

In networking, a URI is a standard way to identify a resource so that systems can find or reference it. It is used in HTTP requests, email headers, REST APIs, and many other protocols.

What is a URI in programming?

In programming, a URI is used to point to files, endpoints, or services. APIs often use URIs to identify resources, for example /users/42 inside a REST endpoint. The URI tells the application which resource to act on.

What is a request URI?

A request URI is the part of an HTTP request that tells the server which resource the client wants. It usually includes the path and the query string, for example /glossary/uri?ref=blog.