关于 libferris： witme.sourceforge.net/libferris.web

扩展属性表： witme.sourceforge.net/libferris.web/research/eadescriptions.html

Xapian::QueryParser 语法： www.xapian.org/docs/queryparser.html

libferris 常见问题解答： witme.sourceforge.net/libferris.web/research/faq.html#relativetime, witme.sourceforge.net/libferris.web/research/faq.html#pgplsqltsearch2 和 witme.sourceforge.net/libferris.web/research/faq.html#agents