The Dangers of Cannibalizing Data Models

[Arnold Rots]

As anybody knows, who has been around for a while, I have always
objected to the practice of cherry-picking components from STC, since
it destroys the integrity of the model: there is no guarantee that the
metadata are either self-consistent or complete anymore.
And Utypes are a form of doing this.

Anybody also knows that I am aware that this is a lost cause,
regrettable as it may be.

However, this week we saw a prime example of how things can break down.
Pierre le Sidaner complained that in ObsTap he could not characterize
time appropriately.
Of course not: it contains a Time Scale, but adding a Time Reference
Position was deemed not to be necessary.
So, he added something (forgot what he called it) and gave it the
value "LOCAL".
This is a case that the standard provides for: a Reference Position on
the Time axis with value "TOPOCENTER".

But because the STC elements have been cherry-picked, the integrity of
the data model was lost and users have no idea that there there may be
solutions in the standard for problems they encounter - and they
invent their own.

Don't blame Pierre; blame the cherry-pickers.
I still believe Utypes are abad idea, because they only reinforce this
practice.
But, as I said, I know this is a lost cause.

  - Arnold


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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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