Re: [DFDL-WG] unordered sequence with constrained occurrences

5 Mar 2013

      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@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!