A schema identifies a field in a document as a key field. Using an XML schema, the key field can be identified by attaching a property to the element or attribute to be used as a key field (if the XML schema standard is modified to support properties). Otherwise, attributes can be used to identify the element or attribute that is to be a key field. Fields can be primary keys, secondary keys, or foreign keys, as supported by data stores. The data store can analyze the schema to determine which fields are key fields. The key fields can be duplicated in the native format of the data store for use in indexing, searching, and other data store functions on the documents. The documents themselves can be stored as objects, into which the data store cannot reach, or can be stored in the native format of the data store, as desired.