- From: Chris Lilley <chris@w3.org>
- Date: Sat, 3 Aug 2002 21:59:04 +0200
- To: www-tag@w3.org, Paul Prescod <paul@prescod.net>
- CC: Bill de hÓra <dehora@eircom.net>
On Friday, August 2, 2002, 8:26:57 PM, Paul wrote: PP> But detecting and dealing with two people using the same identifier to PP> mean different things is hard, because you can never differentiate it PP> from a mere contradiction. "Michael Jackson is white." "No, Michael PP> Jackson is black." Are we disagreeing on Michael's pigment du jour or PP> talking about different Michaels? The standard way to decide is to use PP> an addressing/naming system that we agree is globally unambiguous. "I'm PP> talking about the Michael Jackson with this social security number. Who PP> are you talking about?" You deal with the case where the SSN shows they are different people, but not the case where it shows they are the same person. PP> If, after using a global identifier, we could *still* be talking about PP> two different guys then the global identifier is useless and should be PP> discarded. But if the two SSNs match and you are talking about two different periods in that individuals life, and supposing the details of that lifer were not so well known, then the two people might still disagree that they were talking about the same person, because their invariability assumptions would have been challenged. PP> If we can't depend upon that then you have no way to detect PP> contradictions because you must constantly remain open to the PP> possibility that they are really ambiguities. You can't depend on it, as you sday, and it requires a human to give an estimate of whether it is more likely to be an error or an ambiguity. Different humans will give different answers. To pursue the time-based difference further - based on two point samples of skin coloration in the example above, there was scope for either ambiguity, or for error (which would be given a ghigher probability if the two people conducting the conversation believed that skin pigmentation is invariant). To bring this back to the Web - two people discussing http://www.w3.org/TR/ might agree they are talking about the same thing, over a long period of time. Then again, as soon as someone asserts that the fourth letter of the second word in the fifth paragraph is an "e", then they disagree based on the dates of the respective point samples that they have chosen to use. PP> Another analogy: the credit card companies routinely deal with PP> contradictions: "I bought that. I didn't buy that." But they define away PP> ambiguity. By definition, two credit cards with the same number are the PP> same credit card. If they detect two people using the "same" credit card PP> (number) in conflicting ways they just invalidate the card: they do not PP> split the card into two logical cards and try to deal with the PP> ambiguity. Which is fine until some company in some country starts issuing 'spouse' cards with the same number. PP> They don't tell merchants: "this credit card number is being used PP> ambiguously. Please figure out which of the two people you are talking PP> to." They say: "This credit card number is generating an unreasonable PP> number of contradictory statements. Please ignore that card from now PP> on." That doesn't make it a true statement though, just the one they are currently betting on based on their experience. -- Chris mailto:chris@w3.org
Received on Saturday, 3 August 2002 15:59:32 UTC