[DFDL-WG] unordered sequence with constrained occurrences

[Steve Hanson]

James, 

The error message is because you don't make forward progress through the 
data with potentially unbounded occurrences. Is this because you are using 
a cut-down schema?  If there are delimiters then model those and you might 
not get the error.

Once you have processed the array you can use asserts to check the count. 
However IBM DFDL does not implement the count functions yet.

Give me a couple of days to look at this more closely. I have a customer 
visit tomorrow hence the delay. 

Regards

Steve Hanson
Architect, 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:   "Garriss Jr., James P." <jgarriss at mitre.org>
To:     "dfdl-wg at ogf.org" <dfdl-wg at ogf.org>, 
Date:   05/03/2013 16:19
Subject:        Re: [DFDL-WG] unordered sequence with constrained 
occurrences
Sent by:        dfdl-wg-bounces at ogf.org



Hmmm, maybe not.  I said:
 
> The unordered sequence can be modeled with a data array
 
Yet when implemented in MBTK, it throws a fatal error:
 
fatal: CTDP3148E: Infinite loop at offset 3: The DFDL parser cannot 
process array element 'ABCarray' because maxOccurs is unbounded and the 
length of the previous occurrence was zero. 
 
I think what happens is that on the last pass through the array, it 
doesn’t find a, b, or c, so it throws a fatal error.
 
So is this a bug in MBTK?  Or can DFDL not model an unordered sequence? Or 
am I just doing it wrong?
 
Here’s a sample DFDL schemas that illustrates the point:
 
<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:dfdl="http://www.ogf.org/dfdl/dfdl-1.0/"
      xmlns:fmt="http://www.ibm.com/dfdl/GeneralPurposeFormat"
      xmlns:ibmSchExtn="http://www.ibm.com/schema/extensions" xmlns:xsd="
http://www.w3.org/2001/XMLSchema">
      <xsd:import namespace="http://www.ibm.com/dfdl/GeneralPurposeFormat"
            schemaLocation="IBMdefined/GeneralPurposeFormat.xsd" />
      <xsd:element ibmSchExtn:docRoot="true" name="ABC">
            <xsd:complexType>
                  <xsd:sequence dfdl:separator="">
                        <xsd:annotation>
                              <xsd:appinfo source="
http://www.ogf.org/dfdl/">
                                    <dfdl:sequence />
                              </xsd:appinfo>
                        </xsd:annotation>
                        <xsd:element dfdl:occursCountKind="implicit" 
maxOccurs="unbounded"
                              minOccurs="1" name="ABCarray">
                              <xsd:complexType>
                                    <xsd:sequence dfdl:separator="">
                                          <xsd:element dfdl:length="1" 
dfdl:lengthKind="explicit"
                                                dfdl:occursCountKind=
"implicit" fixed="a" minOccurs="0" name="a"
                                                type="xsd:string" />
                                          <xsd:element dfdl:length="1" 
dfdl:lengthKind="explicit"
                                                dfdl:occursCountKind=
"implicit" fixed="b" minOccurs="0" name="b"
                                                type="xsd:string" />
                                          <xsd:element dfdl:length="1" 
dfdl:lengthKind="explicit"
                                                dfdl:occursCountKind=
"implicit" fixed="c" minOccurs="0" name="c"
                                                type="xsd:string" />
                                    </xsd:sequence>
                              </xsd:complexType>
                        </xsd:element>
                  </xsd:sequence>
            </xsd:complexType>
      </xsd:element>
      <xsd:annotation>
            <xsd:appinfo source="http://www.ogf.org/dfdl/">
                  <dfdl:format ref="fmt:GeneralPurposeFormat" />
            </xsd:appinfo>
      </xsd:annotation>
</xsd:schema>
 
Test with “abc” as sample input.
 
From: Garriss Jr., James P. 
Sent: Tuesday, March 05, 2013 8:43 AM
To: dfdl-wg at ogf.org
Subject: unordered sequence with constrained occurrences
 
Suppose text data has 3 constructs:  a, b, and c.
 
·       a must occur 1 time
·       b can occur 0 or 1 time
·       c can occur any number of times, 0 or more
 
These 3 constructs can appear in any order.
 
So these are valid inputs:
 
abc
a
bcccca
 
But these are not:
 
ccbcc 
abbc
abcabc
 
Can data like this be modeled with DFDL?
 
The unordered sequence can be modeled with a data array, like this:
 
Array (0 to unbounded)
Sequence 
  a (0 to 1)
  b (0 to 1)
  c (0 to 1)
/Sequence
/Array
 
But I don’t know how to constrain the total number of occurrences. 
 
Appreciate any ideas!--
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