The non-denial of the non-self
September 2, 2006
Ooooh, I just love this one. It’s a very welcome diversion for a lazy Saturday morning. Its subtitle is “How philosophy can help create secure databases,” but don’t let that worry you
Cryptography | The non-denial of the non-self | Economist.com
N THE 1940s a philosopher called Carl Hempel showed that by manipulating the logical statement “all ravens are black”, you could derive the equivalent “all non-black objects are non-ravens”. Such topsy-turvy transformations might seem reason enough to keep philosophers locked up safely on university campuses, where they cannot do too much damage.
Yes indeed. Now, the following is for you, Linda, to explain.
What interested Dr Esponda was how the immune system represents information. Here, “everything” is the set of possible biological molecules, notably proteins. The immune system is interesting, because it protects its owner from pathogens without needing to know what a pathogen will look like. Instead, it relies on a negative database to tell it what to destroy. It learns early on which biological molecules are “self”, in the sense that they are routine parts of the body it is protecting. Whenever it meets one that is “not self” and thus likely to be part of a pathogen, it destroys it. In Hempel’s terms, this can be expressed as “all non-good agents [pathogens] are non-self”.
Which leads the author to this thought:
A database of names, addresses and Social Security numbers (a common form of identification in America) might require only 200 characters to contain all possible combinations. That would limit the total number of character combinations. A positive database containing all the data in question would be a small subset of those combinations. The negative counterpart of this database would be much larger and contain all possible names and addresses that were not in the positive database plus a lot of gibberish. But it would not be infinite. By looking at the negative database, it would be possible to deduce what was in the positive database it complemented.
OK, Larry, it’s your turn. Is this something we should lose sleep over?
Dad, waiting patiently on the sidelines for illumination with Laura and Leslie.
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Amazing stuff, immunology. The pictures in books show little puzzle monsters eating only those invaders that fit their mold. All in full color, solely in some biology illustrator’s imagination. The horror is when something goes amuck and antibodies form against ’self’ in one of the auto-immune diseases. L
Don’t know if that’s an explanation or not, but thanks, anyway. Now on to the database design.