1. One or more computer-readable media storing computer-executable instructions that, when executed by one or more processors, configure the one or more processors to perform acts comprising: executing a portable application stored on a portable storage device, wherein the portable application is executed with a functionality or behavior particular to the portable storage device and the portable application as stored; building a portable database having metadata pertaining to the portable application; intercepting a request for data intended for a system database to allow execution of a function related to the portable application; determining whether at least part of the requested data exists in the portable database; determining whether at least part of the requested data also exists in the system database; and reading the requested data from the portable database without reading the requested data from the system database when at least part of the requested data does not also exist in the system database.