As others have pointed out, what you're describing isn't a fundamentally new idea or even that revolutionary. You're basically describing a database filesystem. Onne Gortner attempted an implementation of this concept in 2004 as part of his/her master's thesis (see http://dbfs.sourceforge.net/). Systems like Spotlight are effectively a partial implementation of this concept- OS X essentially has a hybrid setup where there's both a database and conventional filesystem running in parallel. Going back further, locate (first implemented in 1982) could almost be viewed as a proto-Spotlight. Gmail's labels/tags are another example of a mainstream implementation of this.