Next: Proposed CREATOR Keyword
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
- where use of a hyphen is established usage, as for example in the
- 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 188.8.131.52).
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
- Values of the TTYPEn 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.
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