URI URL URN

Excerpt from: http://web.jobbole.com/83452/

A Uniform Resource Identifier (URI) provides a simple, extensible way to identify resources. The semantics and syntax in the URI specification are derived from the concept of the Global Information initiative introduced by the World Wide Web, which has been used since 1990 and is described as "Uniform resource descriptors in the World Wide Web".

Difference

First, let's make one thing clear : URLs and urns are a subset of URIs .

In other words, both the URL and the urn are URIs, but the URI is not necessarily a URL or urn. To better understand the concept, look at this picture below.

With the following example (from Wikipedia), we have a good understanding of the difference between a urn and a URL. If it is a person, we will think of his name and address.

A URL is similar to an address, and it tells you a way to look for a goal (in this case, find a person by street address). You know, the above definition is also a URI.

In contrast, we can think of a person's name as a urn, so a urn can be used to uniquely identify an entity . Because there may be a case of the same name (same surname), it is not quite appropriate to say more accurately the example of a person's name. What's more appropriate is the book's ISBN code and the serial number of the product within the system, although it doesn't tell you how or where to find the target, but you have enough information to retrieve it.

Tim Berners-lee, the inventor of the World Wide Web, is also the head of the World Wide Web Consortium. The photos are provided by Paul Clarke following the CC BY-SA 4.0 protocol.

The following is from:

A URI can represent a domain, or it can represent a resource.

A URL can represent only one resource.

Similarly, a URN (Uniform Resource name) is a subset of URIs and is not currently used on a large scale.

PS:

The URI is a string format specification and does not specify its purpose
URL is a resource location specification including URL FTP server file path

Western Poison
Links: http://www.zhihu.com/question/21950864/answer/19833802
Source: Know
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URI URL URN