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 relate 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, the database schema comprising a database field type identifier and the document schema comprising an XML element data type identifier that maps to the database field type identifier to facilitate converting content data between the XML element data type and the database field type based on the database field type identifier and the XML element data type identifier.