1. van Herwijnen, E.: ‘Practical SGML’, (Kluwer Academic Publishers 1994)
2. Raggett, D., Hors, A., and Jacobs, I.: ‘HTML 4.01 specification’, 1999 December),W3C recommendation
3. Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and Yergeau, F.: ‘Extensible markup language (XML) 1.0 (3rd edn.)’, 2004 February),http://www.w3.org/TR/2004/REC-xml-20040204/, W3C recommendation
4. Fallside, D.: ‘XML Schema Part 0: Primer’, 2001 May),http://www.w3c.org/TR/2001/REC-xmlschema-0-20010502/, W3C recommendation
5. Baeza-Yates, R., and Ribeiro-Neto, B.: ‘Modern information retrieval’, (Addison-Wesley 1999)