[fitsbits] Fwd: Re: The CONTINUE and HIERARCH Conventions Public Comment Periods

[Walter Jaffe]

Just for those who don't know the background of the HIERARCH keywords:

ESO stores the 'state' of all its instrument subsystems in a
tree-form, hierarchal database, with nodes, branches, leaves
etc.  They originally bought this database, including hardware,
from HP, but meanwhile have implemented it themselves in a
UNIX form.  When recording the output data, as FITS images
or tables, it is convenient for them to describe the status
of the instrument by a more or less literal dump of the
data base into the primary header, hence the HIERARCH keyword 
structure.  The system programmers have some choice in which nodes 
they want to dump, but most of them are dumped automatically.
The internal ESO database does not restrict keywords,
formats etc to FITS standards, so if the system designer
is not careful, you get conflicts.  ESO discipline in this
regard is not tight.

My personal view of this is that if you want to record
a database, be it relational, hierarchic, or whatever,
you should choose a format well adapted to the
database format.  If you want to dump a relational
database, use FITS tables; if you want to store a
tree-base, invent a structure that represents this well
and register this convention rather than misuse the
FITS KEYWORD conventions.

Walter