Is anyone using the experimental BLOB feature in Daffodil.
(https://s.apache.org/daffodil-blob-feature)
If so, please reply, or you can email me directly.
This BLOB feature was added as we thought it would be used for the
pixels of images.
I've not seen any questions about it or discussion since it got implemented.
I do know that it is used in the NITF DFDL schema on github, but the
test data for that schema does *not* use that element at all, so
nothing that is part of that schema exercises the feature.
I ask because this extension to DFDL v1.0, if used, would be a strong
candidate for inclusion in the next version of the DFDL specification
(from OGF and ISO).
But.... if nobody is using the BLOB feature, that means other
techniques are sufficient, and then there will be push back within the
DFDL Workgroup against adding this feature to DFDL as part of the
standard.
Personally, I have used this idea for "blobs" of data:
<element name="pixels" dfdl:lengthKind="explicit" dfdl:length='{ ...
the big blob length ...}'>
<complexType>
<sequence>
<element name="blob" dfdl:lengthKind="implicit">
<!-- this blob element allows a dfdl:outputValueCalc='{
dfdl:contentLength(..../pixels/blob) }' to work to capture the length
when unparsing -->
<complexType>
<sequence>
<!-- Avoid giant lines. This is XML. Users *may* want
to open it in a text editor.
Note max size of blob is 100000100.
-->
<element name="a" type="xs:hexBinary" minOccurs="0"
maxOccurs="1000000" dfdl:lengthKind="explicit" dfdl:length="100"
dfdl:occursCountKind="implicit"/>
<element name="last" type="xs:hexBinary"
minOccurs="0" maxOccurs="1" dfdl:lengthKind="delimited"/>
</sequence>
</complexType>
</element>
</sequence>
</complexType>
</element>
That combined with the use of EXI to avoid the XML text bloat seems
like it would address most needs.
