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Subject: Re: [emergency] Forwarded note from David Ellis
OK, I think see the problem ... the data
dictionary doesn't explicitly describe it as a
string (although it is defined as such in the
schema.)
Generally speaking I think it's poor programming
to assume a constraint that isn't in the spec...
in this case, to assume that a null value will
never appear in this field. However, if it will
make life easier for folks either to warn
explicitly that null values may occur, or to
explicitly ban them in the dictionary and the
schema, I certainly wouldn't object.
Of those two options, my personal preference (a
mild one) would be for an advisory note rather
than a technical restriction... mainly on the
theory that it keeps our options open and also
that it's more robust in the long run than trying
to protect against every possible bit of brittle
coding. (It also covers the standard
empty-element equivalent form of "<code/>"... the
very existence of which seems to suggest that
empty elements are a fact of XML life.)
I don't imagine adding the required null-checks
would be an onerous burden for implementers once
the point is clarified.
- Art
>>NOTE on Null String Comment: The data
>>dictionary for code element in both the CAP 1.0
>>and 1.1 states �Any user-defined flag or
>>special code used to flag the alert message for
>>special handling�. This causes many
>>programmers to think of this as a status
>>integer or some numeric priority code for the
>>message. Because this is a string and null is
>>allowed if other CAP implementers sends the
>>code tag with blank content the programs using
>>non-string content often fail. If there is a
>>best practices policy, CAP programs should not
>>send optional tags with null content and should
>>perform checks for now string uses of tags. I
>>am open to helping work some implementation
>>and/or testing guidance.
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