phantom attribute?

I'm seeing some odd behavior when I parse XML with the schema that I just
developed.  In particular, there are two elements, 'signal' and 'method',
which may contain an element, 'arg'.  In the case of 'method', the element
'arg' may have a 'direction' attribute.  However, in the case of 'signal',
the 'arg' element may NOT have a 'direction' attribute.

 

I've represented this in my schema, as follows:

 

<xs:complexType name="signal_arg_type">

                                <xs:sequence>

                                                <xs:element
maxOccurs="unbounded" minOccurs="0" ref="annotation"/>

                                </xs:sequence>

                                <xs:attribute ref="name"/>

                                <xs:attribute name="type"
type="arg_and_property_type" use="required"/>

                </xs:complexType>

 

                <xs:complexType name="method_arg_type">

                                <xs:attribute ref="name"/>

                                <xs:attribute name="type"
type="arg_and_property_type" use="required"/>

                                <xs:attribute default="in" name="direction"
type="arg_direction"/>

                </xs:complexType>

 

<xs:element name="method">

                                <xs:complexType>

                                                <xs:choice
maxOccurs="unbounded" minOccurs="0">

                                                                <xs:element
maxOccurs="unbounded" minOccurs="0" ref="annotation"/>

                                                                <xs:element
maxOccurs="unbounded" minOccurs="0" name="arg" type="method_arg_type"/>

                                                </xs:choice>

                                                <xs:attribute ref="name"
use="required"/>

                                </xs:complexType>

                </xs:element>

 

                <xs:element name="signal">

                                <xs:complexType>

                                                <xs:choice
maxOccurs="unbounded" minOccurs="0">

                                                                <xs:element
maxOccurs="unbounded" minOccurs="0" name="arg" type="signal_arg_type"/>

                                                                <xs:element
maxOccurs="unbounded" minOccurs="0" ref="annotation"/>

                                                </xs:choice>

                                                <xs:attribute ref="name"
use="required"/>

                                </xs:complexType>

                </xs:element>

 

 

Strangely enough, when I parse XML with signal elements, I end up with
SAXParseExceptions that say that the 'arg' element in 'signal' is not
allowed to have a 'direction' attribute, even though the xml that caused the
exception does not contain the 'direction' attribute!!  For example, here is
one of the elements that causes the exception:

 

<signal name="DeviceAdded">

      <arg name="udi" type="s"/>

 </signal>

 

As you can see, there's no 'direction' attribute.  How is it possible that
my parser could be throwing these exceptions, given the schema that I
described above?!  

 

Thanks, in advance, for any feedback.