Subject: Is MD5 based URIs unique? Resent-Date: Sat, 18 Dec 1999 07:04:42 -0500 (EST) Resent-From: www-rdf-interest@w3.org Date: Sat, 18 Dec 1999 13:03:59 +0100 From: Jonas Liljegren To: Sergey Melnik , RDF Intrest Group References: 1 , 2 , 3 Sergey Melnik wrote: > > In the implementation of an RDF API [1] the following algorithm is used: ... > whereas d(x) is the MD5 (128 bit ;) hash of x. The MD5 solution does solve the problem of giving equal URI for equal triples. And the URI's not too long. But I fon't like that they are not guaranteed to be unique. It's one thing to use a MD5 digest as a checksum. In those cases, you would use the digest in pair with another unique identifier, like the file name (and origin URI). It's like how you use the passwords. The passwords doesn't have to be unique. But that is because they are always used with a username that is guaranteed to be unique. There is a greate difference between using a checksum for a control for just one object, and to trust it to be globaly unique. Those genereated URIs would have to be unique in the whole of internet. It doesn't feel right that you would have to take a chanse that you COULD mix up two diffrent triples. I could be wrong. But a 128 bit number would be something between 1 and 340,000,000,000,000,000,000,000,000,000,000,000,000. That seems much today. But what about twenty years from now? What if everything would bee in RDF triples? The golbal net could total up to very large number. Maby a net of 1e9 devices with 1e15 triples each. Maby much more. What if every machine on the planet would depend on that there will never be a mix up of triples? With 340 billions comparsions per second, there could be one mix up every second. Now, even if there is a very small possability of a mixup. Would we still take it, if it was the matter of nuclear power plant or space shuttle or maby some AI taking a decision on the type of surgery for a patient. If 128 bits seems over and well beyond what is required today. Maby we should use 1024 bits? Maby there are a better solution? -- / Jonas - http://paranormal.o.se/perl/proj/rdf/schema_editor/