Sep 20

URL versus URI

Most folks who explore the World Wide Web with a browser application like Microsoft Internet Explorer or Mozilla Firefox are familiar with the URL acronym. URL stands for “Uniform Resource Locator” according to the World Wide Web (W3) consortium. Pronunciation of URL should always be with each letter emphasized (y?-?r-el) instead the fairly common alternative, “earl.” A URL identifies an internet resource and provides the means to locate that resource.

This is all well and good but I keep seeing references to URI in various technical documents and almost exclusively in the documentation of my blogging software, WordPress. Investigation into this acronym started at Wikipedia because it’s so much easier to digest search results in comparison to the rather cryptic W3 site. The information at Wikipedia helped me to better understand how these acronyms relate to each other. URI stands for Uniform Resource Identifier. And although commonly used synonymously with URL, it is actually a different animal.

A Uniform Resource Identifier (URI), is a compact string of characters used to identify or name a resource. The main purpose of this identification is to enable interaction with representations of the resource over a network, typically the World Wide Web, using specific protocols. URIs are defined in schemes defining a specific syntax and associated protocols.

A URI is like the parent of children named URL and URN. Their relationships are best illustrated with this image.

So a URI uses a scheme like “HTTP”, “FTP”, “mailto”, “urn”, “tel”, “rtsp”, to identify a resource. A URL provides the specific location of the resource (like a street address). And a URN defines the identity of a resource (what versus where).


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