Subject: Re: OFSP Proposal on the use of EXTNAME,EXTCLASS & EXTTYPE keywords (v 93-Jun-17)

From: Lucio Chiappetti <[email-masked]>
Date: Fri, 18 Jun 1993 06:53:32 -0400

On Thu, 17 Jun 1993 [email-masked] wrote:

> 	-------------------------------------------------------
> 	|   THE USE OF THE EXTNAME KEYWORD AND THE PROPOSED   |
> 	|	   INTRODUCTION OF TWO NEW KEYWORDS	      |
> 	-------------------------------------------------------
> 					  Version: 1993 June 17
> 
> The OFSP recommends the use of the EXTNAME keyword be changed (at least 
> within the OGIP), and that two new keywords, EXTCLASS & EXTTYPE be 
> introduced:
> 
> EXTNAME   - Can be any string & is essentially not used by OGIP s/w
> EXTCLASS  - Is a new string describing the sort of dataset stored (see below)
> EXTTYPE   - Is a new string available to give more specific details on
>             exactly what type of data is stored (see below)
> 

  I am really perplexed by this proposal, and I fail to see a clear
  distinction between what is used for inter-package data exchange (i.e.
  to make the file readable, or at least understandable to a "foreign"
  package) and what is used exclusively within a GIVEN package.

  My approach would be to use EXTNAME to classify in a broad sense the
  kind of file. In particular in the high energy astrophysics context
  the "kinds of files" I am using are :

     'SPECTRUM'               count/s (or photon/s) spectra
     'RATE'                   time profile (anything vs time)
     'PHOTON LIST'            list of photons or events

      in addition to these I consider images and response matrices
      (but in my view they are images, not bintables, therefore do
      not use EXTNAME)

  If each one of those supports variations, these are either in the
  form (e.g. number and names of columns; and therefore are self-docu-
  mented by other standard keywords like TTYPEn TFORMn etc.), or are
  in the semantics (which is relevant within a particular package
  only, and can be described by whatever optional keyword).

  Being my primary interest in the possibility of EXCHANGING data
  (i.e. importing/exporting them from/to my own package to/from other
  packages) I would as far as possible avoid the use of "specialized"
  convention, which may force to have a dedicated conversion utility
  for each package, instead of a generic reader. 

  As a conclusion, I do not see why you cannot use EXTNAME (instead
  of EXTCLASS) for the top-level classification (to be kept to a FEW
  classes, essentially the ones I listed above ... the exact names 
  can be agreed if you are concerned with imbedded blanks, or more 
  than 6 or 8 characters), and whatever YOU like for the bottom level
  classification. 
  Still, I perceive that the top-level classification (EXTNAME) is
  of relevance within the X-ray (HEAFITS) community (but not necessarily
  within a larger - fitsbits - community), while the lower level
  classification is only "private" to your software.