Hi!

>> If historic data is within the scope of OSM then it surely is not only
>> of interest for railways.  Therefore a generic way of tagging should
>> be used that can apply to any object.  Maybe removed=yes|<date>
>>[..]
> But then we get into the messy situation of not being able to read off
> a single tag to decide what type of feature something is.

I don't get it. - You still know it's a railway, a highway, a
building, ... . Reading more tags will unveil the name, the operator,
the source and so on. There is no difference to a possible 'removed'
-tag. We've alway had certain key-tags that give clues about the type
of an object, others define properties. An easy example would be the
pair highway and name.

> Not all data clients are likely to implement a tag that means the
> logical opposite of the existence of a feature.
>
Which 'removed' would not be. It's an objects property just like name
is. Anyway, I'd like to suggest the pair 'since=<timestamp>' and
'until=<timestamp>' (with the current widely accepted implicated value
'ever' for not given tags).

Regards
   Andreas

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