Re: TV Broadcast URI Schemes Requirements

From: Craig A. Finseth (fin@finseth.com)
Date: Mon, Nov 29 1999


Date: Mon, 29 Nov 1999 15:55:20 -0600 (CST)
Message-Id: <199911292155.PAA04538@isis.visi.com>
From: "Craig A. Finseth" <fin@finseth.com>
To: jeff.sussna@quokka.com
Cc: www-tv@w3.org
Subject: Re: TV Broadcast URI Schemes Requirements

	...
      3. The document states that "given a URI, it must be possible for a
   receiver
      to actually locate the resource, or conclude that it is not reachable?"
      Doesn't this rely on the presence of extrenal software? I.e., URN
   resolvers
      and the like?

   No, it relies on mapping tables.  All resolution is handled in the
   receiver.  The assumptions section clearly indicates that any scheme
   must operate in a "receive only" mode.

   RESPONSE: In my mind, a mapping table IS a URN resolver. Anyway, it still
   seems beyond the scope of the URI spec.

Clarification noted.  We agree.

      6. To restate my above comment more generally, I would add to the
      requirements that a TV URI must completely describe the content being
      identified. In other words, a TV resource identifier must in fact
   uniquely
      (either by location in the case of URL or equality in the case of URN)
      identify a TV resource. 

   It does this.

   What it does not do (by design) is tell you from inspection how to
   obtain the content (it is impossible to do this while remaining
   transport independent): it relies on transport-dependent mapping tables
   for this portion of the system.

   RESPONSE: Yes, it does this, except in the case where a URI returns multiple
   resources. This seems to me to go against at least the spirit of URI's. It

Well, in an environment where you...

1) Identify episodes, and the same episode appears more than once in
the schedule.

2) Identify data modules, and the same module comes around more than
once in a carousel.

I think that a URI returning multiple resources at least matches what
quite a few people expect it to.  (If you'd rather, think of them as
multiple instances of the same resource.)

   also makes me uncomfortable to think about a scheme where I don't know
   exactly what I'll get except in some content-provider specific way. Note

Keep in mind also that in many cases, the same person is creating the
content and assigning the URIs.  There should be few surprizes when
resolving URIs.

   that Apache had the notion of content negotiation which never quite made it
   to universality, and thus never was fully usable.

Pity.  It was a good idea and we needed it.

Craig