I used to work at blist (now called Socrata) where we had to solve this exact problem. You could use a schema-less database - either a document store like Couc

I used to work at blist (now called Socrata) where we had to solve this exact problem. You could use a schema-less database - either a document store like CouchDB, or a schema-less table/column store like Cassandra or Tokyo Tyrant. Or you could use a standard RDBMS and generate new tables on the fly. (This is what blist did when I worked there; I think they may have a different storage model now.) Or implement a column store or tuple store as a layer on top of the RDBMS, like Infobase: http://openlibrary.org/about/tech http://openlibrary.org/about/tech