[OSM-talk] Tagging schema

[Martin Koppenhoefer]

2009/10/5 Andrew Errington <a.errington at lancaster.ac.uk>:
> On Mon, October 5, 2009 15:36, Lester Caine wrote:
> <snip>
>> ( Egil - a little aside, while a check box for boolean would be nice,
>> there is still an element of 'NULL' - that is in addition to setting a
>> boolean tag, one still needs to decide if it should or should not be
>> present )
>
> Checkboxes these days /can/ represent three states.  There are usually two
> states: checked (or ticked) and not checked (an empty white box).  In most
> GUIs it is possible to represent a third state, perhaps a grey square
> filling the box.  (This is different from the control being disabled,
> usually shown by being greyed-out).  The meaning of this third state
> depends on the application, but it can mean NULL, unknown, conflicting
> source data, or whatever you want it to mean when it's not True or False.
>
> I'm not sure that this third state is particularly useful or intuitive,
> but I know it means something different to True or False when I see it.

in JOSM-Preset there are indeed three states: yes, no and notset.

Cheers,
Martin