RE: How does array[i] refer to the i'th item in another array?

[Costello, Roger L.]

Hello DFDL community,

I found an exchange between Steve Lawrence and Lukasz Wiechec back in 2016 that 
seems to suggest a possible solution to my question.

I created this group:

<xs:group name="current_Occurs_Count_Hidden_Group">
    <xs:sequence>
        <xs:element name="current_Occurs_Count" type="xs:nonNegativeInteger"
            dfdl:inputValueCalc="{ dfdl:occursCount() }" />
    </xs:sequence>
</xs:group>

I referenced that group from an element within the repeatable <Section_Wrapper> 
element:

<xs:element name="Section_Wrapper"
    maxOccurs="unbounded"
    dfdl:occursCountKind="expression"
    dfdl:occursCount="{ 
../Headers/File_Header/Number_of_Sections_in_the_Section_Table}">
    <xs:complexType>
        <xs:sequence>
            <xs:sequence 
dfdl:hiddenGroupRef="current_Occurs_Count_Hidden_Group" />
            <xs:element name="Section" type="xs:hexBinary"
                dfdl:lengthKind="explicit"
                dfdl:lengthUnits="bytes"
                dfdl:length="../../Section_Table/Section[position() eq 
../current_Occurs_Count]/Size_of_Raw_Data" />
        </xs:sequence>
    </xs:complexType>
</xs:element>

However, that yields this error message:

'../../Section_Table/Section[position() eq 
../current_Occurs_Count]/Size_of_Raw_Data' is not a valid value of union type 
'DFDLNonNegativeInteger_Or_DFDLExpression'.

I don't know what that error message means.

What to do?

/Roger


From: Costello, Roger L.
Sent: Sunday, December 23, 2018 5:23 PM
To: users@daffodil.apache.org
Subject: How does array[i] refer to the i'th item in another array?

Hello DFDL community,

My DFDL schema has this array:

<xs:element name="Section_Header"
                   maxOccurs="unbounded"
                  dfdl:occursCountKind="expression"
                   
dfdl:occursCount="{../../Headers/File_Header/Number_of_Sections_in_the_Section_Table}">

Each <Section_Header> element contains information about a following <Section> 
element.

Later in the schema is an array of <Section> elements. The array must have the 
same number of elements as Section_Header. I can easily specify the number of 
occurrences of this second array:

<xs:element name="Section"
                   maxOccurs="unbounded"
                   dfdl:occursCountKind="expression"
                   dfdl:occursCount="{ fn:count(../Section_Header) }">

I would like to reference elements within <Section_Header>. For example, there 
is a <Size_of_Raw_Data> element that I would like to use:

If the i'th <Section_Header> element has
               <Size_of_Raw_Data>100</Size_of_Raw_Data>,
               then the i'th <Section> element must have a
               size of 100 bytes.

How does the i'th <Section> element refer to the i'th <Section_Header> element? 
 I think that I need something like this:

<xs:element name="Section"
                   maxOccurs="unbounded"
                   dfdl:occursCountKind="expression"
                   dfdl:occursCount="{ fn:count(../Section_Header) }"
                    type="xs:hexBinary"
                    dfdl:lengthKind="explicit"
                    dfdl:lengthUnits="bytes"
                    dfdl:length="../Section_Header[i]/Size_of_Raw_Data"/>

Of course, the above value of dfdl:length is not correct, as [i] is not 
defined. So, how to do this?

/Roger