Message-ID: <D181361D7C86D011925700805FFE898E019715F6@spybem01.nap.spyglass.com> From: "Adams, Glenn" <firstname.lastname@example.org> To: "'Gomer Thomas'" <email@example.com>, Warner ten Kate <firstname.lastname@example.org> Cc: www-tv <email@example.com> Date: Tue, 3 Nov 1998 10:30:40 -0600 Subject: RE: URL: Background and Requirements -----Original Message----- From: Gomer Thomas [mailto:firstname.lastname@example.org] Sent: Tuesday, November 03, 1998 10:03 AM To: Warner ten Kate Cc: www-tv Subject: Re: URL: Background and Requirements I don't agree with your comments about home/local servers, if I understand them correctly. When I download a file from an Internet server and store it on my local disk, the URL needed to reference the copy on my disk is different from the URL needed to reference the original copy on the Internet server. Similarly, if I record the 6 o'clock news from channel 5 and store it on my local disk, I would expect that the URL needed to reference the local copy on my disk would be different from the URL needed to reference the original broadcast. Aside from the difference in location, the new copy is now available to me at any time, whereas the original broadcast was only available to me at a specific date-time. The storage of content for reuse in a temporally constrained manner should be considered in the context of user agent caches. Clearly, the end user will not be explicitly retaining this content under most (perhaps all) circumstances; rather the user agent will be implicitly retaining it in its cache for transient reuse. The caching of such content is typically keyed upon the original URI, usually in an absolute URI form. In the present discussion, given that no return channel to a server would be expected, revalidation of cached content would not be possible; instead, content freshness would be computed based on explicit expiration data and served out of the cache on that basis. See section 13 (Caching in HTTP) of HTTP/1.1 <http://www.ietf.org/internet-drafts/draft-ietf-http-v11-spec-rev-05.txt > , presently in Internet Draft form. Given the semantics of caching and cache entry freshness, it is quite reasonable to employ a URI in embedded content (e.g., in HTML) that references content that changes as programs change. The expiration times of cached content would be keyed to the surrounding broadcast content. Furthermore, if some content were pushed with a given expiration time and it was later determined that the content should be replaced or the expiration time updated, then new content could be pushed through to the cache which updates either its content, its freshness data, or both. Regards, Glenn Adams Spyglass, Inc.