What is the difference between URI, URL and URN?
This question already has an answer here:
Uniform Resource Identifier ( URI ) is a string of characters used to identify a name or a resource on the Internet
A URI identifies a resource either by location, or a name, or both. A URI has two specializations known as URL and URN.
A Uniform Resource Locator ( URL ) is a subset of the Uniform Resource Identifier (URI) that specifies where an identified resource is available and the mechanism for retrieving it. A URL defines how the resource can be obtained. It does not have to be HTTP URL (http://), a URL can also be (ftp://) or (smb://).
A Uniform Resource Name ( URN ) is a Uniform Resource Identifier (URI) that uses the URN scheme, and does not imply availability of the identified resource . Both URNs (names) and URLs (locators) are URIs, and a particular URI may be both a name and a locator at the same time.
The URNs are part of a larger Internet information architecture which is composed of URNs, URCs and URLs.
bar.html is not a URN . A URN is similar to a person's name, while a URL is like a street address. The URN defines something's identity, while the URL provides a location. Essentially, "what" vs. "where". A URN has to be of this form <URN> ::= "urn:" <NID> ":" <NSS> where <NID> is the Namespace Identifier, and <NSS> is the Namespace Specific String.
To put it differently:
I'd say the only thing left to make it 100% clear would be to have an example of an URI that is not an URL. We can use the examples in the RFC3986:
URL: ftp://ftp.is.co.za/rfc/rfc1808.txt
URL: http://www.ietf.org/rfc/rfc2396.txt
URL: ldap://[2001:db8::7]/c=GB?objectClass?one
URL: mailto:John.Doe@example.com
URL: news:comp.infosystems.www.servers.unix
URL: telnet://192.0.2.16:80/
URN (not URL): urn:oasis:names:specification:docbook:dtd:xml:4.1.2
URN (not URL): tel:+1-816-555-1212 (?)
Also check this out - https://quintupledev.wordpress.com/2016/02/29/difference-between-uri-url-and-urn/
Below I sum up Prateek Joshi's awesome explanation.
The theory:
That is:
And for an example:
Also, if you haven't already, I suggest reading Roger Pate's answer.
URL -- Uniform Resource Locator
Contains information about how to fetch a resource from its location. For example:
http://example.com/mypage.html ftp://example.com/download.zip mailto:user@example.com file:///home/user/file.txt http://example.com/resource?foo=bar#fragment /other/link.html (A relative URL, only useful in the context of another URL) URLs always start with a protocol ( http ) and usually contain information such as the network host name ( example.com ) and often a document path ( /foo/mypage.html ). URLs may have query parameters and fragment identifiers.
URN -- Uniform Resource Name
Identifies a resource by name. It always starts with the prefix urn: For example:
urn:isbn:0451450523 to identify a book by its ISBN number. urn:uuid:6e8bc430-9c3a-11d9-9669-0800200c9a66 a globally unique identifier urn:publishing:book - An XML namespace that identifies the document as a type of book. URNs can identify ideas and concepts. They are not restricted to identifying documents. When a URN does represent a document, it can be translated into a URL by a "resolver". The document can then be downloaded from the URL.
URI -- Uniform Resource Identifier
URIs encompasses both URLs, URNs, and other ways to indicate a resource.
An example of a URI that is neither a URL nor a URN would be a data URI such as data:,Hello%20World . It is not a URL or URN because the URI contains the data. It neither names it, nor tells you how to locate it over the network.
There are also uniform resource citations (URCs) that point to meta data about a document rather than to the document itself. An example of a URC would be an indicator for viewing the source code of a web page: view-source:http://example.com/ . A URC is another type of URI that is neither URL nor URN.
Frequently Asked Questions
I've heard that I shouldn't say URL anymore, why?
The w3 spec for HTML says that the href of an anchor tag can contain a URI, not just a URL. You should be able to put in a URN such as <a href="urn:isbn:0451450523"> . Your browser would then resolve that URN to a URL and download the book for you.
Do any browsers actually know how to fetch documents by URN?
Not that I know of, but modern web browser do implement the data URI scheme.
Can a URI be both a URL and a URN?
Good question. I've seen lots of places on the web that state this is true. I haven't been able to find any examples of something that is both a URL and a URN. I don't see how it is possible because a URN starts with urn: which is not a valid network protocol.
Does the difference between URL and URI have anything to do with whether it is relative or absolute?
No. Both relative and absolute URLs are URLs (and URIs.)
Does the difference between URL and URI have anything to do with whether it has query parameters?
No. Both URLs with and without query parameters are URLs (and URIs.)
Does the difference between URL and URI have anything to do with whether it has a fragment identifier?
No. Both URLs with and without fragment identifiers are URLs (and URIs.)
Is a tel: URI a URL or a URN?
For example tel:1-800-555-5555 . It doesn't start with urn: and it has a protocol for reaching a resource over a network. It must be a URL.
But doesn't the w3C now say that URLs and URIs are the same thing?
Yes. The W3C realized that there is a ton of confusion about this. They issued a URI clarification document that says that it is now OK to use URL and URI interchangeably. It is no longer useful to strictly segment URIs into different types such as URL, URN, and URC.
链接地址: http://www.djcxy.com/p/1896.html上一篇: URL和LINK有什么区别？
下一篇: URI，URL和URN有什么区别？