1. An apparatus for defining a metadata schema to facilitate passing data between an extensible Markup Language (XML) document and a hierarchical database, the apparatus comprising: a database accessor configured to access a database schema indicative of database field names and a hierarchical structure for a hierarchical database; a document accessor configured to access a document schema that defines the hierarchical structure, content data syntax, and semantics of valid, well-formed, XML documents that can be passed into and out of the hierarchical database, the document schema including an XML element name that maps to a database field name in the database schema; and an association module configured to associate the database schema and the document schema to provide a metadata schema that enables data to be passed between an XML document and the hierarchical database.