| Quick-Start Introduction to PDS Archiving |
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Expanding the Data Dictionary
Sometimes you will not be able to find the right keyword or standard value
for a parameter you want to document, or your data just won't seem to fit
comfortably into any of the existing PDS OBJECTs. In these cases, the first
thing to do is to contact your coordinating discipline node for advice, since
these situations are not uncommon. Some are easier to fix than others, and
your node contact can advise you on what the optimal solution is and take care
of any necessary paperwork with the Central Node (the Data Standards arm)
of the PDS. The usual
course of action in each case is described below.
Note:
It is, of course, easier on everybody if these potential problems are
identified as early as possible in the ingestion process.
If the keyword you want to use doesn't have the standard value you
need...
This is an easy one. Contact your discipline
node and provide for them a description
of the standard value you'd like to use and what it means. The node will
make sure it really doesn't duplicate anything already in the Data Dictionary
and pass it along to the Central Node, who will incorporate it into the
Dictionary as part of the ingestion process for the data set.
If you can't find a keyword that does the job...
Explain to your contact node exactly what you're trying to define. The node
will do a thorough search of the Data Dictionary to make sure the proposed
new keyword doesn't duplicate any other and take care of preparing the
file needed to submit a new keyword to Central Node for cataloging. Central
Node will also get the new keyword and, if it seems appropriate, ask other
nodes to review it before incorporating it into the Data Dictionary.
There is a little more inertia involved in creating new keywords because,
in general, keywords should be broadly applicable rather than project-specific.
Consequently, care is taken in ensuring that the definition is precise enough
for the keyword to be meaningful, but not so specific as to preclude its use
in other data sets. When there is a need for it, however, keywords are added
to the dictionary, so data preparers should feel free to request them when
necessary.
If none of the standard PDS OBJECTs seems quite right...
This is a much more serious problem. The PDS OBJECTs provide the basis on
which general-use software is being built for accessing and retrieving data.
Also, the structures involved are those that are most accessible to the
majority of users. There are certainly data sets out there that don't fit
into the standard formats easily, but experience has shown
that users strongly prefer that the data be in a more accessible format
than in, say, the most compact.
It's not impossible to add a new OBJECT to the PDS system, but the amount
of justification required is, understandably, great.
Consequently, if your data really don't fit into any of the PDS OBJECTs, you
will probably be strongly urged to reformat your data to fit into the
OBJECT structure which best represents the logical structure of the data.
Your contact node can provide advice and perhaps some tools to assist in
reformatting the data. For projects doing production-line processing of
a large number of files, you will probably be best off writing a
post-processing routine to reformat the data and generate the PDS labels
simultaneously.
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