VEP-007.txt

Vocabulary: http://www.ivoa.net/rdf/datalink-core
Author: Baptiste Cecconi <baptiste.cecconi@obspm.fr>
Date: 2021-06-09

Term: #detached-header
Action: Addition
Label: Detached Header
Description: Machine-readable metadata for #this, which in general 
will be necessary for its scientific use.  Examples include FITS 
headers distributed without their data blocks or PDS label files. 
Relationships: rdfs:subPropertyOf(documentation)
Used-in: http://voparis-tap-maser.obspm.fr/voyager_pra/epn/dl/dlmeta?ID=VG1-J-PRA-3-RDR-LOWBAND-6SEC-V1.0%3APRA_I.TAB

Term: #documentation
Action: Modification
Description: Structured or unstructured metadata helping to understand, 
  interpret, or work with #this.  Such information can range from
  processing logs to weather reports to technical documents on
  instruments to related publications.


Rationale:
  In some formats and archives, the metadata required to decode the 
  content of #this is in a separate file. In the case of NASA/PDS 
  data products, for example, the PDS label file contains the decoding 
  metadata. In some archives, the FITS header may be stored separately 
  as a plain text file, next to a data file consisting of a binary 
  stream of bytes. Clients would use the content type (MIME type) 
  (e.g.: application/x-pds4-label+xml, or text/x-pds3-label) to enable 
  the processing.

  As to the change of the definition of #documentation, is essentially
  dropping the previous requirement of it being "human readable".  On
  closer inspection it turned out that humans will always need tools to
  interpret bitstreams, and hence "human-readability" is not a useful
  and reproducable criterion to define concepts.  Perhaps at some point
  we will have to tell apart structured and non-structured metadata so
  computers can ignore non-structured documents.  As long as detached
  headers are the only sort of structured metadata computers look for in
  datalink documents, there does not seem to be sufficient reason for
  introducing this distinction.

Discussion:
  In the thread at 
  http://mail.ivoa.net/pipermail/semantics/2021-June/002806.html,
  the proposal was received favourably.  There was a proposal to perhaps
  add a wider term *#metadata, but given there already is #documentation
  which probably covers a large part of such a concept already, no
  immediate need was brought forward.

  On the other hand, the discussion brought up that #documentation
  explicitly asked for "human-readable text form".  This certainly is
  not the case for many important sorts of detached headers, and even
  for FITS headers one can debate this.   In consequence, the VEP was
  amended to also fix #documentation's definition (cf.
  http://mail.ivoa.net/pipermail/semantics/2021-September/002846.html).

  The VEP was accepted in the present from at the TCG session of
  2021-10-27.