empty values for ?Text (answer to #1414)

Richard Durbin rd at sanger.ac.uk
Fri Oct 10 04:48:10 EST 1997


Dave Matthews says he used to use "" or " " for ?Text where he wanted 
to skip an item in a multiple-item field, as in

>   Probe : "xyz"
>   Wheat_polymorphism "" HindIII "0.0 (1,13)"

We made this illegal in 4_5.  This was necessary because all items in
a class must have a unique name, and the 0th item with an implicit
empty name was already used for storing the model.  (Remember that
?Text is a handled as a class just like ?Probe). It turns out that
using "" gave spurious references to the models, and even allowed
people to edit the models in alarming ways.  This was definitely a
bug/loophole.

I suggest that you use some symbol such as "-" as a convention for
missing data.

You can still have empty Text, as opposed to ?Text.

Richard




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