Re: [guppi-list] goose datatype system

[Jon Trowbridge <trow emccta com>]

Sent this only to Asger by mistake...

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• From: Jon Trowbridge <trow>
• To: "Asger K. Alstrup Nielsen" <alstrup diku dk>
• Subject: Re: [guppi-list] goose datatype system
• Date: Mon, 30 Nov 1998 11:59:39 -0600

I'm going to think more carefully about Asger's comments before saying
too much more, but I will throw out one thing that I neglected to
mention before --- the feature that I think is one of the larger
defects of the "double" system, at least from an aesthetic standpoint:

The DataSet defines a lot of operations that are really not defined
for other data types.  After all, it is completely bogus to calculate
the skewness of a set of unordered categorical data.

For dates, what should you be able to do (besides access individual
data elements): find the min and max date.  That is the only
meaningful operation that I can think of off the top of my head.

Ordered categorical data: first and last category, and an easy way to
get a list of all categories.

Unordered categorical data: nothing, except for the list of
categories.

Another thing to think about is that the "double" approach gives us a
sort of polymorphism for free, but it might actually be inappropriate.
For example, most statistical operations are not flexible in this
regard: either a test requires categorical data, or it doesn't.  We
don't gain anything by having everything be a DataSet (except for
avoid the need to write a lot of code), just as we don't gain anything
by defining a DataSetBase virtual class and using it as the base class
for everything, and then defining our functions to take DataSetBase
pointers as args...

More later.

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