Re: Identifying by location -- Was: A pk is *both*...

David Cressey wrote:
...
> Paul C,
>
> I'd like to try to reframe this discussion by changing the context from
> "The part with lot number 203 at location 22" to another item that is
> commonly identified by location. I'm thinking of web pages.
>
> A hyperlink embedded in HTML text does not specify the identity of the page
> pointed to, but rather its location. Recall that the "L" in URL stands for
> "LOCATOR". It's possible to break a hyperlink simply by moving the target
> page. "Moving" can be construed as a two step process: creating a copy at
> a new location, and destroying the copy at the original location.
>
> How many of us have experienced the frustration of following a link that we
> rely on, only to get the dreaded "Error 404" (Page not found). There are
> billions of broken hyperlinks out there. The question might arise whether
> it isn't irresponsible on the part of the one who moves a page not to put a
> jump page back at the original location. Aside from being extra work, this
> carries problems of its own.
>
> In essence, when you use locators as if they were identifiers in a reference
> system, you're back to the graph model of data. A similar problem occurs
> when you try to move a record in one of the old network (e.g. CODASYL)
> databases. The existing references to the record require for their stbility
> that the targeted record be "pinned" to its current location.
>
> So, looking at it this way, the web is the largest graph there is. Pages
> may be pinned, and there is no way for the owner of a page to know that it
> is not pinned.

Thanks, this is definitely more interesting, at least to me. Maybe the "404" situation should be subject to "delete cascade" (just kidding). I think I've read the double-entendre term "stateless" describing http. Something always seemed missing, still does, no offence to Berners-Lee, but Codd was a little different, ie. he crossed disciplines in a way that to me was much more profound. Before his papers, I believe that logic was mostly considered just an application, whereas one of his points was saying, let's make an system for writing apps that IS classical logic, not one that is merely loosely based on the kind of logic found in a classical non-computer field. If Codd had talked about "references" without restricting them to "primary keys", I sometimes wonder what would have happened. OTOH, I guess that probably the http author could well have been more or less ignorant of what Codd was saying (and he wouldn't have been the first on that score). Even wrong ideas can take on a life of their own when they just happen to be useful to many people on a widespread scale. History of so-called civilization/technology, I guess.

I must go and look closer at the http variation that has something to do with transactions. I vaguely remember laughing when I first saw it, but maybe I was wrong. My reaction was a little like Groucho Marx's when a publisher he knew asked him to write a jacket blurb for some comic author's book. He wrote back something like "from the moment I picked it up until I put it down, I couldn't stop laughing. Someday I'm going to read it". I wondered if the stateless camp ever dug that a stateless system is possibly the canonical vehicle for the implementation of a transaction (which I suspect) or are they oblivious? My first impression was that the http people were closer to right than the tcp transaction protocol authors, but not as close as the netscape people who made the first cookies.

p

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Received on Tue Jul 31 2007 - 02:57:45 CEST