[tm-pubsubj-comment] Subject Indicator Fingerprints [WAS: Genetic PSIs[Re: Topic Map domain, paradigmatic PSIs ...]]

[Kal Ahmed <kal@techquila.com>]

Firstly, thanks to Bernard for bringing up yet another intersting "thought 
for the day"!

I can't resist putting on my developer's hat when I read this and try and 
figure out how a PSI could be successfully "replicated" and yet still 
remain identifiable with minimal processing.

I see an issue here between the forms of identification and resolution 
mechanisms so far proposed for PSIs and the pursuit of stability through 
replication, but fortunately, this is not an issue which has not already 
been addressed by those developing decentralized information sharing 
systems and although no expert in this field, I suspect that an answer may 
be lurking in some clever application of cryptographic hashes to a 
published subject indicator. Some application such as this would allow a 
subject indicating resource to be copied wholesale from the original 
publisher to another site, (thus reassigning subject indicating resource's 
address), yet its origin could still be securely and consistently 
identified (at least in theory...as I say, I'm no expert on this subject 
;-). An application could then determine a PSI's fingerprint by retrieving, 
validating and finally digestifying the content - assuming that all is OK, 
this would lead to a match. This might seem like a lot of overhead, but in 
a distributed system, it is the price of information security - of course, 
in a more controlled environment, various short-cuts could be applied. For 
example, a "subject indicator directory service" might retrieve and 
validate the multiple addresses for the same subject indicating resource 
and then publish a topic map which consists merely of alternate subject 
indicating resource addresses for the subjects it aggregates.

While the forgoing is somewhat fuzzy, my feeling is that the PSI group 
should consider that a location-dependent subject indicating resource 
address (such as an HTTP address) is not necessarily a barrier to the 
robust replication of subject indicating resources, but that in order for 
it not to be a barrier, another level of technology may be required for 
such a location-independent scheme to be trust-worthy in an open system.

Cheers,

Kal