1. A tangible computer-readable storage medium, comprising: a data structure stored on the computer-readable storage medium comprising a plurality of extensible markup language (XML) instances, at least two XML instances of said plurality of XML instances are stored in a column of a database, and said at least two XML instances do not conform to the same XML schema, and said column of the database is designated for storing XML data according to an object that represents two or more XML schema namespaces, wherein XML instance comprises a set of XML data conforming to a structure provided by XML schema, XML schema identifies and organizes data in an XML instance, and XML schema namespace is used to ensure unique naming of elements and attributes in an XML schema.