What is the definition of an absolute URL (fully qualified?)

问题

There are (at least) three ways to link to a resource:

href="foo/bar.html"
href="/foo/bar.html"
href="http://example.com/foo/bar.html"

The first is a "relative url", no problem. But I've seen (2) and (3) both referred to as an "absolute url". Which is correctly termed an "absolute url", and what is the proper name of the other?

(Bonus points for references to relevant standards or other official documentation.)

回答1:

RFC 3986 defines Uniform Resource Identifiers.

A relative reference that begins with a single slash character is
termed an absolute-path reference. A relative reference that does
not begin with a slash character is termed a relative-path reference.

href="foo/bar.html" is a relative reference, specifically a relative-path reference.
href="/foo/bar.html" is a relative reference with an absolute path
href="http://example.com/foo/bar.html" is an absolute URI
href="//example.com/foo/bar.html" is a network-path reference

A relative reference that begins with two slash characters is termed a network-path reference; such references are rarely used.

回答2:

"Absolute URLs contain a great deal of information which may already be known from the context of the base document's retrieval, including the scheme, network location, and parts of the URL path."

http://tools.ietf.org/html/rfc1808

The number (2) is an absolute path, the (3) is an absolute URL.

回答3:

Only #3 fits the definition of absolute URL. 1 & 2 are relative URLs.

A relative URL (defined in [RFC1808]) doesn't contain any protocol or machine information, and its path generally refers to an HTML document on the same machine as the current document. Relative URLs may contain relative path components (".." means the parent location) and may be fragment URLs. Source: http://www.w3.org/TR/WD-html40-970708/htmlweb.html

A URL is an absolute URL if resolving it results in the same output regardless of what it is resolved relative to, and that output is not a failure. Source: http://www.w3.org/TR/url/

回答4:

RFC 3986 (URI Generic Syntax) specifies in section 4.3. Absolute URI the following rule:

absolute-URI = scheme ":" hier-part [ "?" query ]

Therefore, #2 is not an absolute URI

回答5:

I believe (2) is also a relateive URL and (3) is an absolute URL.

http://kb.iu.edu/data/abwp.html shows some examples.

On http://www.wisegeek.com/what-is-an-absolute-url.htm, it explains it as this:

"An absolute URL gives complete location information. It begins with http:// and continues, including every detail. This means that if the webmaster were to change the location of the original file, an absolute URL specification would find the image, while the relative URL specification would not."

回答6:

I like the W3's description found here:

A URL is an absolute URL if resolving it results in the same output regardless of what it is resolved relative to, and that output is not a failure.

It doesn't bring up scheme, path, or any other concepts like that, but basically just says that the same input always brings the same output. You can only say that about #3.

I wouldn't get too caught up in the technicalities though - #2 is still absolute if your universe is the website. Also something like //example.com/foo/bar.html is absolute if your universe is the scheme. I think the word "absolute" in those cases is still meaningful from a developer's perspective.

回答7:

The term I've heard for #2 is "root relative". I believe this is a useful definition as its meaning is clear in the wording and readily distinguishes it from #1 and #3.

回答8:

Supporting the other answers with some further visual examples.

https://datacash.custhelp.com/app/answers/detail/a_id/1067/~/fully-qualified-url

A fully qualified URL contains the http:// (or https://www). If the URL is just your domain, the trailing / should also be provided.

These URLs are fully qualified:

http://www.datacash.com/
https://www.datacash.com/
http://datacash.com/
https://datacash.com/
http://www.datacash.com/Transaction.html
https://www.datacash.com/Transaction.html
http://datacash.com/Transaction.html
https://datacash.com/Transaction.html

These URLS are not fully qualified:

datacash.com
datacash.com/
datacash.com/Transaction.html
www.datacash.com
www.datacash.com/
www.datacash.com/Transaction.html
http://datacash.com
https://datacash.com
http://www.datacash.com
https://www.datacash.com

来源：https://stackoverflow.com/questions/17406848/what-is-the-definition-of-an-absolute-url-fully-qualified

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