Re: How do you validate against an external DTD

David Bertoni Fri, 23 Jan 2009 14:06:39 -0800

Dantzler, DeWayne C wrote:

Hello
I'm currently using Xerces C++ 2.7.0 DOM Parser. I want to validate
against an external DTD specified by the caller and not the DTD called
out in the XML document. How is this done with the Xerces API?

The easiest way is with an EntityResolver or a DOMLSResourceResolver,depending on which parsing interface you're using.


Here's what I've done.

 Code snippet:
 ==========================================================
//perform the necessary DOM Parser init and setup ... omitting all the
gory details

//setup the Entity Resolver to redirect the parser to use the external

DTD//to resolve external ENTITY's and not the DTD called out in the XML

file by the DOCTYPE declaration
//The entire XML file will also be validated against the external DTD as
well
                
        csCtkXmlEntityResolver *resolver = new
csCtkXmlEntityResolver(dtd); <<--- caller specified dtd
        _XmlDOMParser->setEntityResolver(resolver);
                
        //Turn on the necessary features to allow validation by an

external DTD_XmlDOMParser->setValidationScheme(_XmlDOMParser->Val_Always);

        _XmlDOMParser->setDoSchema(false);                   
        _XmlDOMParser->setLoadExternalDTD(true);

This value is true by default.


        //TODO - How do you load an external DTD???
        //Not sure if this routine does it, but I'll give it a try and
it didn't!!

        _XmlDOMParser->loadGrammar(dtd, Grammar::DTDGrammarType, false);

You've loaded the grammar, but told the parser not to cache it, so itknows nothing about it. Please pass 'true' as the last parameter.

        _XmlDOMParser->setSkipDTDValidation(false);
        _XmlDOMParser->useCachedGrammarInParse(true);

        ....
        //attempt to parese the XML and get pages of errors             
        }
==============================================================

Results: Lots of Parser Errors but several of the elments are definedin the DTD


<?xml version="1.0" encoding="UTF-8"?>
line 2::column 6: <bcme
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";

Parser Error Message: Unknown element 'bcme'

<?xml version="1.0" encoding="UTF-8"?>
line 2::column 17: <bcme
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";

Parser Error Message: Attribute 'xmlns:xsi' is not declared for element
'bcme'

<?xml version="1.0" encoding="UTF-8"?>
<bcme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
line 3::column 33:
xsi:noNamespaceSchemaLocation="http://www.boeing.com/commercial/cas_xml/
s1000d/3-0BE1-3/schema/bcme.xsd">

Parser Error Message: Attribute 'xsi:noNamespaceSchemaLocation' is not
declared for element 'bcme'

==============================================================
XML Doc Snippet

<?xml version="1.0" encoding="UTF-8"?>
<bcme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";

xsi:noNamespaceSchemaLocation="http://www.mycompany.com/cas_xml/schema/a

cme.xsd">
  <edition>
    <editionid>BCMM-21-21-03-81205_20080301.1207260301</editionid>
    <editionType>New</editionType>
    <editionNumber>1207260301</editionNumber>
  </edition>
==================================================================

This document looks like it uses a schema for validation, not a DTD. Ingeneral, documents that are structured to use XML schema for validationcan be difficult to validate using a DTD. You might still get somevalidation errors, depending on the instance document, and how flexiblethe DTD is.


Dave

Re: How do you validate against an external DTD

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