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[fitsbits] Fwd: The CONTINUE and HIERARCH ConventionsPublic Comment Periods
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 |
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