[DFDL-WG] empty sequences

[Steve Hanson]

See this errata:

2.48. Section 14.1. Spec states that an empty sequence that is the content 
of a complex type is a schema definition error. Many schema processors are 
not able to distinguish this condition from a complex type with no content 
at all (it is not required to do so by the XML Schema specification). As a 
complex type with no content is not useful in DFDL, change the spec to 
state that both conditions are schema definition errors. 

This was raised by Sandy Gao of the W3C XSD WG.

So your example...

<complexType name="headerRowType">
   <sequence dfdl:initiator="name%WSP+;address%WSP+;phone" 
dfdl:terminator="%NL"/>
</complexType>

...would be treated by some XSD processors as...

<complexType name="headerRowType">
</complexType>

...and the DFDL annotations lost.

You can always use a nested sequence.

Regards

Steve Hanson
Architect, IBM Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848



From:   Mike Beckerle <mbeckerle.dfdl at gmail.com>
To:     dfdl-wg at ogf.org, 
Cc:     Jessie Chab <jchab at tresys.com>
Date:   24/04/2013 17:21
Subject:        [DFDL-WG] empty sequences
Sent by:        dfdl-wg-bounces at ogf.org




This section of the spec seems wrong:

14.1 Empty Sequences
A sequence having no children is syntactically legal in DFDL. In the data 
stream, such a
sequence can have non-zero length LeftFraming and RightFraming regions, 
but the
SequenceContent region in between must be empty. It is a processing error 
if the
SequenceContent region of an empty sequence has non-zero length when 
parsing.

XML schema does not define an empty sequence that is the content model of 
a complex type
definition as effective content so any DFDL annotations on such a 
construct would be ignored. It
is a schema definition error if the empty sequence is the content model of 
a complex type, or if a
complex type has nothing in its content model at all.

This seems like it is both legal and useful:

<complexType name="headerRowType">
   <sequence dfdl:initiator="name%WSP+;address%WSP+;phone" 
dfdl:terminator="%NL"/>
</complexType>

So the statement, DFDL annotations on such a construct would be ignored, 
is not right. 

And also a complexType sequence might actually have content via 
dfdl:hiddenGroupRef.

<complexType name="hiddenGroupType">
   <sequence dfdl:hiddenGroupRef="myHiddenGroup"/>
</complexType>

So the statement that the region in-between left and right framing must be 
empty is also not right.

Comments?


-- 
Mike Beckerle | OGF DFDL Workgroup Co-Chair | Tresys Technology | 
www.tresys.com
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