[译]URL和URI的区别
The Difference Between URLs and URIs
Uniform Resource Identifier (URI): Generic Syntax
1.1.3. URI, URL, and URN
A URI can be further classified as a locator, a name, or both. The
term "Uniform Resource Locator" (URL) refers to the subset of URIs
that, in addition to identifying a resource, provide a means of
locating the resource by describing its primary access mechanism
(e.g., its network "location").
URI可被视为定位符（URL），名称（URN）或两者兼备。
Uniform Resource Identifier
统一资源标志符
A Uniform Resource Name (URN) can be compared to a person's name, while a Uniform Resource Locator (URL) can be compared to their street address. In other words, a URN identifies an item and a URL provides a method for finding it.
URLs
A URL is a URI that, in addition to identifying a web resource, specifies the means of acting upon or obtaining the representation of it, i.e. specifying both its primary access mechanism and network location. For example, the URL http://example.org/wiki/Main_Page refers to a resource identified as /wiki/Main_Page whose representation, in the form of HTML and related code, is obtainable via Hypertext Transfer Protocol (http) from a network host whose domain name is example.org.
URL是一种URI，它标识一个互联网资源，并指定对其进行操作或获取该资源的方法。可能通过对主要访问手段的描述，也可能通过网络“位置”进行标识。
URNs
A URN is a URI that identifies a resource by name in a particular namespace. A URN may be used to talk about a resource without implying its location or how to access it. For example, in the International Standard Book Number (ISBN) system, ISBN 0-486-27557-4 identifies a specific edition of Shakespeare's play Romeo and Juliet. The URN for that edition would be urn:ISBN0-486-27557-4. To gain access to the book, its location is needed, for which a URL would have to be specified.
URN是基于某命名空间通过名称指定资源的URI。人们可以通过URN来指出某个资源，而无需指出其位置和获得方式。资源无需是基于互联网的。
用于标识唯一书目的ISBN系统是一个典型的URN使用范例。