1. A computer memory having stored therein information comprising: schema data that includes metadata for each of a plurality of database structures, said metadata specifying, for each of the plurality of database structures, primitive fields of the respective database structure, and data types of said primitive fields; and executable program code configured to run on a server and to use the schema data, including said metadata for each of the plurality of database structures, to at least: (1) encode instances of said database structures in cookie data for storage on user computers, and (2) reproduce instances of said database structures in a memory of said server from cookie data received from user computers.