An XML database is a data persistence software system that allows data to be specified and sometimes stored, in XML format. This data can be queried, transformed, exported and returned to a calling system. XML databases are a flavor of document-oriented databases which are in turn a category of NoSQL database.
There are a number of reasons to directly specify data in XML or other document formats such as JSON. For XML in particular, they include:
Steve O’Connell gives one reason for the use of XML in databases: the increasingly common use of XML for data transport, which has meant that “data is extracted from databases and put into XML documents and vice-versa”. It may prove more efficient (in terms of conversion costs) and easier to store the data in XML format. In content-based applications, the ability of the native XML database also minimizes the need for extraction or entry of metadata to support searching and navigation.
XML enabled databases typically offer one or more of the following approaches to storing XML within the traditional relational structure:
RDBMS that support the ISO XML Type are:
Typically an XML enabled database is best suited where the majority of data are non-XML. For datasets where the majority of data are XML, a native XML database is better suited.