Re: [xsl] [XSLT Streaming] I xsl:iterate over airport primary records; how do I get the following sibling airport continuation record?

["Martin Honnen martin.honnen@xxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

On 31/01/2025 20:25, Roger L Costello costello@xxxxxxxxx wrote:
> Hi Folks,
>
> I am stream-processing a huge air navigation file that contains, among other
things, airport primary records:
> <ARINC>
>          ...
>          <record>
>                  <ARINC_424-18_4_1_7_1_Airport_Primary_Records>
>                      data about an airport
>                 </ARINC_424-18_4_1_7_1_Airport_Primary_Records>
>          </record>
>          ...
> </ARINC>
>
> In my program, I iterate over the airport primary records:
>
> <xsl:iterate
select="ARINC/record/ARINC_424-18_4_1_7_1_Airport_Primary_Records">
>      process an airport
> </xsl:iterate>
>
> Some--not all--airport primary records have a continuation record, which
immediately follows--is the first following sibling--the airport primary
record:
> <ARINC>
>          ...
>          <record>
>                  <ARINC_424-18_4_1_7_1_Airport_Primary_Records>
>                      data about an airport
>                 </ARINC_424-18_4_1_7_1_Airport_Primary_Records>
>          </record>
>          <record>
<ARINC_424-18_4_1_7_3_Airport_Flight_Planning_Continuation_Records>
>                      additional data about the airport
</ARINC_424-18_4_1_7_3_Airport_Flight_Planning_Continuation_Records>
>          </record>
>          ...
> </ARINC>
>
> Within the xsl:iterate loop, I tried to obtain the following continuation
record and store it into a variable:
> <xsl:iterate
select="ARINC/record/ARINC_424-18_4_1_7_1_Airport_Primary_Records">
>      <xsl:variable name="flt-pln-cont"
select="copy-of(../following-sibling::record[1]/ARINC_424-18_4_1_7_3_Airport_
Flight_Planning_Continuation_Records)"/>
>      process the airport and its continuation data
> </xsl:iterate>
>
> When I run my program, I get this error message:
>
> Static error at xsl:source-document on line 10 column 47 of
create-airports.xsl:
>    XTSE3430  The body of the xsl:source-document instruction is not
streamable
>    *  Cannot use the following-sibling axis when context posture is CLIMBING
(line 16)
>    *  Expression
parent::(element()|document-node())/following-sibling::record[1] requires
>    sorting nodes into document order
>
> What is the correct way to do this?

With streamings, you process each node once in a forwards only way.

It is not clear to me why you process e.g.
ARINC/record/ARINC_424-18_4_1_7_1_Airport_Primary_Records if a "record"
element can also contain e.g.
ARINC_424-18_4_1_7_3_Airport_Flight_Planning_Continuation_Records, your
outer xsl:iterate would already have skipped the
ARINC_424-18_4_1_7_3_Airport_Flight_Planning_Continuation_Records
elements if it only looks for ARINC_424-18_4_1_7_1_Airport_Primary_Records.

As for ways to solve this, it is not clear how large a "record" element
is, e.g. if you perhaps could just use

B  <xsl:iterate select="ARINC/record!copy-of()">

B B B B B  <xsl:param name="previous-record" as="element(record)?"
select="()"/>

B B B B  <xsl:next-iteration>
B B B B B B  <xsl:with-param name="previous-record" select="."/>

B  B B  </xsl:next-iteration>

B  </xsl:iterate>


There are also capturing accumulators (a Saxon extension in XSLT 3 but
streaming is only implemented by Saxon anyway) that can help store nodes.

Or streaming with e.g.

B B  <xsl:for-each-groups select="ARINC/record!copy-of()"
group-starting-with="record[ARINC_424-18_4_1_7_1_Airport_Primary_Records]">

None of that is pure streaming, of course, but unless you buffer the
"ARINC_424-18_4_1_7_1_Airport_Primary_Records" data in a map I don't
think there is a way to look back with streamed processing.