Buongiorno,
sto cercando di imparare ad utilizzare hibernate, ho iniziato cercando di seguire il seguente articolo postato su html.it
articolo
Una lanciato il programma mi viene generata questa eccezione:

Exception in thread "main" org.hibernate.InvalidMappingException: Could not parse mapping document from resource Persona.hbm.xml
at org.hibernate.cfg.Configuration.addResource(Config uration.java:616)
at org.hibernate.cfg.Configuration.parseMappingElemen t(Configuration.java:1635)
at org.hibernate.cfg.Configuration.parseSessionFactor y(Configuration.java:1603)
at org.hibernate.cfg.Configuration.doConfigure(Config uration.java:1582)
at org.hibernate.cfg.Configuration.doConfigure(Config uration.java:1556)
at org.hibernate.cfg.Configuration.configure(Configur ation.java:1476)
at org.hibernate.cfg.Configuration.configure(Configur ation.java:1462)
at stefania.PersonaUnitTest.main(PersonaUnitTest.java :14)
Caused by: org.hibernate.InvalidMappingException: Could not parse mapping document from invalid mapping
at org.hibernate.cfg.Configuration.addInputStream(Con figuration.java:549)
at org.hibernate.cfg.Configuration.addResource(Config uration.java:613)
... 7 more
Caused by: org.xml.sax.SAXParseException: Document is invalid: no grammar found.
at com.sun.org.apache.xerces.internal.util.ErrorHandl erWrapper.createSAXParseException(ErrorHandlerWrap per.java:195)
at com.sun.org.apache.xerces.internal.util.ErrorHandl erWrapper.error(ErrorHandlerWrapper.java:131)
at com.sun.org.apache.xerces.internal.impl.XMLErrorRe porter.reportError(XMLErrorReporter.java:384)
at com.sun.org.apache.xerces.internal.impl.XMLErrorRe porter.reportError(XMLErrorReporter.java:318)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocum entScannerImpl.scanStartElement(XMLNSDocumentScann erImpl.java:250)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocum entScannerImpl$NSContentDriver.scanRootElementHook (XMLNSDocumentScannerImpl.java:626)
at com.sun.org.apache.xerces.internal.impl.XMLDocumen tFragmentScannerImpl$FragmentContentDriver.next(XM LDocumentFragmentScannerImpl.java:3095)
at com.sun.org.apache.xerces.internal.impl.XMLDocumen tScannerImpl$PrologDriver.next(XMLDocumentScannerI mpl.java:922)
at com.sun.org.apache.xerces.internal.impl.XMLDocumen tScannerImpl.next(XMLDocumentScannerImpl.java:648)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocum entScannerImpl.next(XMLNSDocumentScannerImpl.java: 140)
at com.sun.org.apache.xerces.internal.impl.XMLDocumen tFragmentScannerImpl.scanDocument(XMLDocumentFragm entScannerImpl.java:510)
at com.sun.org.apache.xerces.internal.parsers.XML11Co nfiguration.parse(XML11Configuration.java:807)
at com.sun.org.apache.xerces.internal.parsers.XML11Co nfiguration.parse(XML11Configuration.java:737)
at com.sun.org.apache.xerces.internal.parsers.XMLPars er.parse(XMLParser.java:107)
at com.sun.org.apache.xerces.internal.parsers.Abstrac tSAXParser.parse(AbstractSAXParser.java:1205)
at com.sun.org.apache.xerces.internal.jaxp.SAXParserI mpl$JAXPSAXParser.parse(SAXParserImpl.java:522)
at org.dom4j.io.SAXReader.read(SAXReader.java:465)
at org.hibernate.cfg.Configuration.addInputStream(Con figuration.java:546)
... 8 more

Non riesco a capire quale sia il problema. Qualcuno ha qualche idea?
Grazie Stefania