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Native XML databases for hierarchical data: preserving the value of XML''s hierarchical structure. (XML & DBMS).

Article Excerpt
XML is widely accepted as the standard for describing data to be exchanged between applications and over the Web. But there is considerably less agreement on how it should be stored and queried.

XML and its predecessor, SGML, have been in existence for a long time without the world of "ordinary" data processing paying too much attention. XML brings with it a whole set of data modeling assumptions, processing mechanisms, and extensibility considerations that have proved useful in document-centric communities, but have had little mindshare in the database world for 20 years.

Hierarchical Structures and the XML Approach

Generally, XML addresses the demand for modeling hierarchical structures in a very elegant way. Modeling information in terms of a component/subcomponent model of the world is made very straightforward. XML elements are containers: they have the ability to contain information content as well as other containers. These containers can contain other containers, and so on.

XML enables its users to deal with highly recursive structures, well suited to concisely express complicated nested relations. Typically, "bill-of-material'-like structures are easily expressed via an XML data model. The containership model, in which containers contain other containers of the same type, has always been familiar to people working with document models, but isn't so familiar to "classical" database designers.

XML designers make use of its ability to deal with the "self-similarity" of document structures. Imagine a data model for scientific research papers that's intended to be open for...

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