'Re: "[xml] How to get elements default values, defined in the schema"'

[Kasimier Buchcik <kbuchcik 4commerce de>]

Hi,

on 9/1/2004 9:12 AM Zhamak Dehghani wrote:
> Hi,
>
> I've used xmlSchema functions i.e. "xmlSchemaValidateDoc(...)" to validate a xml document.
> To read an element's content I have used "xmlNodeGetContent(...)" function.
>
> The schema I use has defined default values for some of the elements i.e. 
> "<xsd:element name="AcquirerName" type="xsd:string" default="WESTPAC" minOccurs="0"/>"
>
> I expected after validating a document against the schema, default values get loaded into the document nodes
> and xmlNodeGetContent to return default values if an element doesn't appear in the xml document or appear 
> with
> an empty content.
> However my assumptions don't seem to be correct. xmlNodeGetContent never returns any values if element
> appears with empty content i.e. "<AcquirerName></AcquirerName>"

You refer to the post-schema-validation infoset [1]: this is not 
implemented yet with the XML Schema processor of libxml2. I guess the 
PSVI and its API to create, will be one of the tail ends of the whole 
implementation story; although I admit that default and fixed values 
would be really a nice-to-have as early as possible.

> and the element node itself doesn't 
> even get created on the tree if the element is missing in the document.

Value constraints of element declarations [2] are handled differently to 
those of attribute declarations (i.e. the element, if missing, is not 
expected to appear in the PSVI):

"{value constraint} establishes a default or fixed value for an element. 
If default is specified, and if the element being ·validated· is empty, 
then the canonical form of the supplied constraint value becomes the 
[schema normalized value] of the ·validated· element in the 
·post-schema-validation infoset·. If fixed is specified, then the 
element's content must either be empty, in which case fixed behaves as 
default, or its value must match the supplied constraint value."

> I appreciate if you could tell me how I can get the schema default values for the elements which are 
> missing or
> have empty content in the document?

As "http://www.xmlsoft.org"; states, the XML Schema processor is 
"work-in-progress". There is currently no functionality available to 
fulfill your needs - feel free to bugzilla it [3] to remind us of its need.

[1] http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#a-schema_default
[2] 
http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#cElement_Declarations
[3] http://bugzilla.gnome.org/buglist.cgi?product=libxml2

Regards,

Kasimier