To find out who you are ...

... you ask what [you are] not. Then you are left with what you are.

That, according to Fernando Esponda, a computer scientist at Yale, is a part of Hindu philosophy. The Economist has a story (with the curious title "The non-denial of the non-self") that describes how this bit of Hindu philosophy may be used for developing reliable and well-protected databases with sensitive data:

The concept of a negative database took shape a couple of years ago, while Dr Esponda was working at the University of New Mexico with Paul Helman, another computer scientist, and Stephanie Forrest, an expert on modelling the human immune system. The important qualification concerns that word “everything”. In practice, that means everything in a particular set of things.

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”.