1. A method comprising: at a respective server system having one or more processors and memory storing one or more programs that when executed by the one or more processors cause the respective server system to perform the method, the method comprising: sending, to a first database, a first request for data based on first data-retrieval criteria, wherein the first database is schemaless and operates in accordance with first database processing capabilities; receiving, in response to the first request, a first set of data from the first database, wherein the first set of data is selected by the first database in accordance with the first data-retrieval criteria; generating a second database from the first set of data selectively retrieved from the first database, wherein the second database has an associated schema and operates in accordance with second database processing capabilities different from the first database processing capabilities; providing access to the first set of data in the second database in accordance with the second database processing capabilities; receiving, from a client, a query that can be processed using data in the second database; processing the query using data in the second database to generate a response; and transmitting the response to the client; wherein processing the query uses at least a respective database processing capability of the second database processing capabilities that is not one of the first database processing capabilities; and the respective database processing capability of the second database processing capabilities is a database processing capability selected from the set consisting of: a capability that is contingent upon the schema being strictly enforced; a capability to process at least one respective query having a query-syntax that is not supported by the first database; a capability to search within content of one or more entities in accordance with one or more query terms provided in the query; a capability to compare a stored metadata value for a data entity to multiple bounding parameters to determine whether the metadata value satisfies a query component corresponding to the multiple bounding parameters; a capability to combine entities from a plurality of different tables of the second database in accordance with criteria specified in the query; and a capability to reject the query in accordance with a determination that the query does not conform to the schema associated with the second database.