[DFDL-WG] DFDL: Applying DFDL annotations to elements

[Steve Hanson]

To apply DFDL annotations to a top-level element in a DFDL xsd, most 
modellers would use the dfdl:element dfdl:ref property to refer to a named 
dfdl:defineFormat block that set up the necessary defaults for all the 
DFDL properties. To avoid having to re-state the dfdl:ref property on 
every object that comprises the format, most modellers would also use the 
dfdl:complexType dfdl:ref property to scope the same dfdl:defineFormat 
block.  The xsd would look like below. 

<xs:schema ...>
  <xs:annotation><xs:appinfo source=?http://www.ogf.org/dfdl/?>
      <dfdl:defineFormat name=?textFormat1">
        <dfdl:format encoding="utf-8" separator="\n" representation=?text? 
lengthKind="delimited" />
      </dfdl:defineFormat>
  </xs:appinfo></xs:annotation>
  ...
  <xs:element name="textDoc" dfdl:ref="textFormat1" 
dfdl:lengthKind="implicit">
           <xs:complexType dfdl:ref="textFormat1">
              <xs:sequence>
            ...
              </xs:sequence>
           </xs:complexType>
  </xs:element>
  ...
</xs:schema>

It's not possible to put DFDL defaults in scope for the whole format with 
a single dfdl:ref property. I think this is a side-effect of removing the 
dfdl:appliesTo property. 

If this is thought to be an issue, there are a couple of options:

One is to say that a complex type can be the top-level object. This is the 
case with several XML based systems. It works with XML because the XML 
instance document provides the name of top level element in the infoset 
via its tag. This is not the case with DFDL where the name is commonly not 
carried with the format. So we'd have no name for the infoset.

Another is to provide a new property on dfdl:defineFormat, which says this 
dfdl:defineFormat is the default for all top-level objects in the xsd. Any 
top-level object that remained silent as to its dfdl:ref would get the 
default applied. I'm not sure whether this makes the model too opaque 
though. No more so than the existing scoping rules, I suspect.

Any other opinions or suggestions welcome.

Regards

Steve Hanson
Programming Model Architect
WebSphere Message Brokers
Hursley, UK
Internet: smh at uk.ibm.com
Phone (+44)/(0) 1962-815848





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