xml files using as databases

xml files are used as databases instead of connecting to databases. This can be done by entring my data in an .xml file as whole? How efficient is this.
They can be accessed and modified client or server side. (how is this ?).
Pls explain me in detail. it wld be a gr8 help.

Thank u very much

here are some of the links I learned from:

http://www.xmlpitstop.com/
http://www.xmlfiles.com/articles/michael/searchxml/default.asp
http://hotwired.lycos.com/webmonkey/98/41/index1a.html
http://www.perfectxml.com/articles/xml/binary.asp
http://www.topxml.com/
http://www.webreference.com/js/column102/6.html
http://www.xmlfiles.com/