[xsd-users] default value xsd and parsing

[Benjamin Schindler]

Thank you a lot for the thorough answer. This cleared everything up

Benjamin

On 02/26/2010 04:06 PM, Boris Kolpackov wrote:
> Hi Benjamin,
> 
> Benjamin Schindler <bschindler at inf.ethz.ch> writes:
> 
>> I have the following thing I'd like to achieve:
>>
>> 	<xs:complexType name="ServerConfiguration_t">
>> 		<xs:sequence>
>> 			<xs:element name="port" type="xs:int" default="5454"/>
>> 		</xs:sequence>
>> 	</xs:complexType>
>>
>> (I tried the same with xs:all instead of sequence)
>>
>> When I get an xml that doesn't have the port attribute, validating the
>> xml fails. But I'd expect that I get an object without the xsd::Optional
>> template which has the default value 5454 if the xml does not have it.
> 
> While you say "port attribute", in the schema you have an element and
> that makes all the difference. The XML Schema spec says that for an
> element to get a default value, an empty element should be present
> in XML, as in:
> 
> <port/>
> 
> In other words, omitting an element from the XML completely doesn't
> result in it having a default value. Rather, if this element is 
> optional, it is treated as no being present and if it is required,
> as in your case, then you will get a validation error. This behavior
> makes attributes with default value an odd construct which is not 
> used much.
> 
> On the other hands, for attributes, the default value is used if the
> attribute is not present, and this is used a lot in schemas.
> 
> There is a table in Appendix A, in the C++/Tree Mapping User Manual
> which summarizes the differences between default values for elements
> and attributes:
> 
> http://www.codesynthesis.com/projects/xsd/documentation/cxx/tree/manual/#A
> 
> Boris