13. The server of claim 12 wherein the catalog defines: an identity of, for each field in the collection, a type of data values populated for the field; if the field is a mixed type, a percentage of data values corresponding to each data type; a count of populated data values for each type; and for each data value, a reference to a location of the data value in the collection.
13. The server of claim 12 wherein the catalog defines: an identity of, for each field in the collection, a type of data values populated for the field; if the field is a mixed type, a percentage of data values corresponding to each data type; a count of populated data values for each type; and for each data value, a reference to a location of the data value in the collection. 15. The server of claim 13 wherein the identified type of the data values is a compound type, the application further configured to recursively identify an atomic data value resulting from decomposition of the compound type; compute a field name based on a concatenation of names of the fields of the compound type; and map the computed field name to a corresponding field in the DB command.