[DFDL-WG] outputValueCalc and unparse example

[Mike Beckerle]

I did not get as far as I wanted to on this issue. I would like to discuss
this example:

 

<sequence>

  <element name="len" type="int" 

 dfdl:fillByte="%#r0;"

    dfdl:outputValueCalc=

      "{

           dfdl:representation-output-length(../val)  

       }" />

 

  ... many elements in between ....

 

  <element name="val" type="string" 

     dfdl:encoding="utf-8"

     dfdl:lengthKind="explicit" 

     dfdl:lengthUnits="bytes" 

    dfdl:useLengthForOutput="false"

     dfdl:length="{ ../len }"

    dfdl:outputLength="{             

         fix:ceiling( 

           dfdl:representation-inherent-length(.) div 4 

           ) * 4 

    }"

 dfdl:textTrimKind="padChar"

 dfdl:textStringJustification="left"

    dfdl:textPadCharacter="%#r0;"                  

    />

</sequence>

 

 

You will notice I added a dfdl:outputLength property, and a
dfdl:representation-output-length() function and
dfdl:representation-inherent-length().

 

I am accepting candidates for better names for these properties and
functions. We need to distinguish these 3 concepts:

 

1) inherent length - of the infoset item without reference to any facets,
and with out respect to escape sequences, padding or truncation. 

 

(TBD: think about escape sequences? Is this right)

 

2) output target length - the length of the box we're filling in with the
data value representation. The box can be bigger or smaller than the
inherent length, which implies use of padding/filling, or truncation.

 

3) input length - length of the box we're getting when parsing. The inherent
length of the value after parsing can be smaller than the length of the box
due to removal of escape characters, and the trimming of padding.

 

 

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