[Playlist] Questions on spec about meaning of identifier and link

[Lucas Gonze]

There is a subtle thing to realize about http:// URIs -- they can be
just identifiers and not at all locators.  Because of this they have
absorbed the function of URNs, which are now a subset of URIs (the
subset which is just an identifier and not a locator).

For example, let's say you wanted to have the recording of the song
"Mandy" on the album "Greatest Hits: The Platinum Collection" by the
artist "Barry Manilow" in your playlist, and you wanted your song
reference to work regardless of where the listener happened to be able
to fetch the song from.

One thing you could do is go look it up on Musicbrainz.org and find
the track page, then use the URI of the track page as the identifier.
That URI happens to be at
http://musicbrainz.org/track/541f8f37-c9f3-4567-b234-9806d25ca433.html
, so the XSPF for this recording would be:

<track><identifier>http://musicbrainz.org/track/541f8f37-c9f3-4567-b234-9806d25ca433.html</identifier></track>

Notice that dereferencing this URI does not give you a copy of the
song.  The URI is just an identifier, and not a locator.

Also, it doesn't matter that this particular URI goes to a page of
text and metadata.  The URI doesn't have to even be real.  It just has
to be usable as an identifier which the publisher and content resolver
can both understand.  For example, the domain example.com is forbidden
(by the rules of DNS) to map to any real world web server, but the URI
http://example.com/track/541f8f37-c9f3-4567-b234-9806d25ca433.html is
perfectly legal in an XSPF identifier element.

-L

(Hey Tomas, nice to see you.  :)

On 6/13/07, Tomas Franzén <tomas at lightheadsw.com> wrote:
> On 13 jun 2007, at 22.12, Ross Mohn wrote:
> > 1. Why does the spec indicate that a track identifier "MUST be a legal
> > URI"? I would think of this element as specifying a CD id code or
> > something of that sort, not a URI. Doesn't the phrase "MUST be a legal
> > URI" conflict with the phrase "location-independent name"?
>
> Hi,
>
> Remember that URIs are not the same as URLs (the L stands for
> Location). URIs can be URNs, meaning something like this (for ISBN
> numbers):
> urn:isbn:0-395-36341-1
>
> Note that the above does not specify a location. It's up the client
> to figure that out.
> Wikipedia has more info. http://en.wikipedia.org/wiki/URI
>
> (Hi everyone, BTW. It's been awhile since I last posted here.)
>
> Tomas Franzén
> Lighthead Software
> http://www.lightheadsw.com/
>
>
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