Re: [xml-dev] validation against xml schema (xsd)

[George Cristian Bina <george@oxygenxml.com>]

Hi Matt,

You can do a first parse and stop once you reach the root element, for 
instance by throwing an exception on the first startElement callback. 
That will give you enough information about the document to determine 
the schema to use. While you do this parse you can buffer what the 
parser reads and then start the validation feeding the parser with the 
buffered content and then the remaining content of your document. You 
can find an example of this in Jing, see the AutoSchemaReader and the 
RewindableReader and RewindableInputStream classes:

http://code.google.com/p/jing-trang/source/browse/trunk/mod/validate/src/main/com/thaiopensource/validate/auto/AutoSchemaReader.java
http://code.google.com/p/jing-trang/source/browse/trunk/mod/validate/src/main/com/thaiopensource/validate/auto/RewindableReader.java
http://code.google.com/p/jing-trang/source/browse/trunk/mod/validate/src/main/com/thaiopensource/validate/auto/RewindableInputStream.java

Best Regards,
George
--
George Cristian Bina
<oXygen/> XML Editor, Schema Editor and XSLT Editor/Debugger
http://www.oxygenxml.com


Johnson, Matthew C. (LNG-HBE) wrote:
> Hello,
> 
>  
> 
> I am wrestling with a choice and would like to ask for opinions.  In 
> validating XML instance documents against a W3C XML Schema instance, I 
> can either rely use @xsi:schemaLocation and rely on it as a hint or I 
> can infer which schema to apply using some other piece of information 
> from the document.  I believe one of the arguments against using 
> @xsi:schemaLocation is that the consuming application should arguably be 
> in a better position to determine which schema to apply than the 
> producer.  This is especially true in situations where a document could 
> be valid against multiple schemas.  My scenario is that a document is 
> either valid or not but I do not want to discount this argument.  
> Another argument against is that it is defined as only a hint and that 
> not all tools support it, although in my case, the tools do support it.
> 
>  
> 
> My question is, if I did not use/provide @xsi:schemaLocation, what are 
> some suggested options and means to determine the schema?  I will almost 
> certainly be using a catalog (OASIS) so I believe this will play a role 
> in the decision.  One option I have considered is using the namespace 
> URI of the root element as a sort of public identifier that could be 
> used by the catalog resolver but this has limited support in 
> “off-the-shelf” parsing solutions.  For example, Xerces (Java) supports 
> this through their (XNI) XMLCatalogResolver class but standard SAX 
> EntityResolver(2) does not expose/report namespaces.
> 
>  
> 
> The piece that is bugging me a little is that, regardless of the means 
> of determining the schema, it feels like an extra 
> step/pass/look-into-the-document is required before the actual parse of 
> the document.  Relying on @xsi:schemaLocation feels much more like 
> relying on a DOCTYPE for a DTD in that it is recognized during the main 
> parsing step represented by a standard API call (e.g. 
> xmlreader.parse(…)) (even if that call does a few passes itself).
> 
>  
> 
> I could even remove the notion of XSD here and ask the same question if 
> I were validating against one of multiple RelaxNG schemas.  Since RNG 
> does not have the standardized equivalent of @xsi:schemaLocation that 
> allows the instance document to say “validate me to this schema”, it 
> feels like a pre-pass would be needed here too.  The Oxygen editor uses 
> a processing instruction to indicate which RNG file it should use for 
> validation but I am unsure whether the implementation first does a pass 
> to get the PI and then another to validate or whether it is able to 
> validate in a single pass.
> 
>  
> 
> Am I missing anything here?  I appreciate any comments, alternatives, 
> etc.  Thanks, I appreciate it!
> 
>  
> 
> Matt
> 
>  
> 
> PS:  My scenario involves collections of heterogeneous content types so 
> each document could be of one of several schema types (but only valid to 
> one).  The effect is that I could not rely on doing a pre-parse (or 
> regex) on the first of a collection and assume that all docs in that 
> collection are the same.
> 
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