[DFDL-WG] DFDL Schema - Mulitple forms of Annotation syntax

[Suman Kalia]

Following forms of annotations syntax is supported on DFDL schema as per 
the 1.33 spec 

1. Shot form syntax 
<xs:element name="foo" type="xs:int" maxOccurs="unbounded" 
dfdl:representation="text" dfdl:initiator="{" dfdl:terminator=”}”/>

Note: It requires all properties to be defined as global attributes in 
schema as each attribute has to be uniquely identifiable and accessible 
within the DFDL namespace

2. Long form syntax ( used for dfdl:format and specialized annotations 
such as dfdl:element etc)

<xs:element name="foo" type="xs:int" maxOccurs="unbounded">
      <xs:annotation><xs:appinfo source=”http://www.ogf.org/dfdl/”>
        <dfdl:format representation="text" initiator=”{“  terminator="}"/> 

      </xs:appinfo></xs:annotation>
</xs:element>

Note: Attributes specified here are not qualified with dfdl namespace 
prefix. It means the attributes have to be defined locally within the 
complex type are not accessible directly (like in the short form syntax)

3.  Long form property representation to ease syntactic expression 
difficulties with data in attribute values: 
  <xs:annotation>
    <xs:appinfo source=”http://www.ogf.org/dfdl/”>
        <dfdl:format>
         <dfdl:property name='encoding'>utf-8</dfdl:property>
         <dfdl:property name='separator'>\n</dfdl:property>
<dfdl:property name=’initiator’><[CDATA[<!-- ]]></dfdl:property>
        </dfdl:format> 
    </xs:appinfo>
</xs:annotation>

Note: The name attribute will be enumeration of base name of all DFDL 
properties (ie without namespace prefix). On the specialized annotations 
(ie dfdl:element) we will also need to have a repeating child element 
definition for dfdl:property. This annotation will appear on specialized 
annotation element for dfdl attributes whose value cannot be stored as XML 
attribute. 
 
PS: Alan - when you update the spec for specialized annotation please 
mention this use case  and put an example also. 

To support  syntax form 1 & 2, it  requires defining all attribute 
definition for each  DFDL property multiple times ie one global attribute 
and a local attribute in the complex type of each long form annotation 
element.  Using Attribute groups we can address the latter issue ie define 
related local attributes once in the attribute group and include the 
attribute group in one or more complex type. But it still requires 
defining the attribute definition for each DFDL property atleast twice (ie 
one global and one local attribute definition).  This duplication can 
potentially lead to inconsistency and inadvertently updating one 
definition and not the other.

One option that we can consider to remove this redundancy is to define 
only the global attribute definition for each DFDL property and include it 
through attribute reference in each of the complex type of  dfdl:format 
and specialized annotations.  The downside of this approach is that 
attributes will appear qualified in the dfdl:format and specialized 
annotation elements. Given below is how the dfdl:format annotation  will 
appear in the user defined schema where each attribute is prefixed with 
dfdl (hilited in green). 

<xs:element name="foo" type="xs:int" maxOccurs="unbounded">
      <xs:annotation><xs:appinfo source=”http://www.ogf.org/dfdl/”>
        <dfdl:format dfdl:representation="text" dfdl:initiator=”{“  dfdl:
terminator="}"/> 
      </xs:appinfo></xs:annotation>
</xs:element>

From technical perspective (e.g. schema integrity , avoiding duplication 
definitions etc.), this is better but it does have usability issue.


Suman Kalia
IBM Toronto Lab
WMB Toolkit Architect and Development Lead
WebSphere Business Integration Application Connectivity Tools 

http://www.ibm.com/developerworks/websphere/zones/businessintegration/wmb.html


Tel : 905-413-3923  T/L  969-3923
Fax : 905-413-4850 T/L  969-4850
Internet ID : kalia at ca.ibm.com
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