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

Wed May 6 19:45:53 CDT 2009

Hmmm. This is the dilemma of is an object different from an instance of its
type.

E.g., if a complex type has a terminator is that the terminator on the
element that has that type?

We could define the syntax you used as redundant:

<element name="foo" dfdl:ref="a">
   <complexType dfdl:ref="a">  // means same thing as if also hoisted onto
the element having this type.
                                             // i.e., ref applies to scope
of complexType AND to elements having this type.
     ...

It is true we do not allow dfdl:ref on the xs:schema element. This is for
very important reasons of keeping us out of the whole lexical vs.
non-lexical scoping morass. Let's not go there. 

  _____  

From: dfdl-wg-bounces at ogf.org [mailto:dfdl-wg-bounces at ogf.org] On Behalf Of
Steve Hanson
Sent: Wednesday, May 06, 2009 1:22 PM
To: dfdl-wg at ogf.org
Subject: [DFDL-WG] DFDL: Applying DFDL annotations to elements

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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