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Keywords and column names
In keywords and table column names, HEASARC recommends use of the
underscore (hexadecimal 5F) rather than the hyphen (hexadecimal
2D). The only cases where a hyphen is to be used in keywords
are
- where use of a hyphen is established usage, as for example in the
DATE-OBS keyword.
- to represent a minus (negation) sign
This set of recommendations is similar to those in the original paper
for ASCII table fields, as discussed in section 3.4.2, but
extends them to keywords and binary table fields. Extending the rules
for keywords to column names makes it possible to replace a table column
heading with a keyword with the same name if the value for that column
in every row of the table is the same, as in the Green Bank convention
(section 5.2.3.2).
HEASARC/OGIP requires the following additional conventions for column
names in all tables it produces and recommends them for others:
- Different columns in the same table cannot have the same name
and all columns must be unique in the first 16 characters.
- Embedded blanks are specifically forbidden, as they are for
keywords.
- Values of the TTYPE keyword are case-insensitive, as
specified for ASCII tables in the NOST standard described in
section 6.1.2.
- Column names must begin with an alphabetic character
(A-Z, a-z), not a digit or underscore.
- Column names may be up to 68 characters in length.
Next: Proposed CREATOR Keyword
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William Pence
2004-01-07