On Mon, Jun 09, 2008 at 11:58:28AM +0100, Richard Fairhurst wrote: || Dave Stubbs wrote: || || > The good point about name=__none__ is that I can bet large amounts of || > money that no street is actually named "__none__" -- the bad points || > are that renderers that don't know about it are going to write it in || > the street name || || So maybe named=no (or unnamed=yes)?
The problem is really more general. You want to be able to say (a): "tag T is absent", as opposed to (b) "nobody has bothered to enter tag T yet". For distinguishing these two, we need to find some way to explicitly specify (a), because (b) has to be modeled by the tag just being not there (think about it). I can see several ways, in personally increasing preference: 1. define a special value for the tag (e.g. "" or "__none__") disadvantage: takes away a technially valid value, so may not be generalizable to tags other than "name". 2. add another (meta) tag specifying which tags are undefined: absent_tags=name,any_other_tag,... disadvantage: this is a multi value tag, which complicates the model. Witness the gratuitous potlach value-combining with semicolons. 3. specify a derived tag, as with localised names: name:absent=yes disadvantage: might accumulate to a lot of extra tags in the database, but it only needs to be added if there really is uncertainty about the situation. So... how about doing T:absent=true? The interpretation of which being: tag T is not there in the real world, as opposed to only not there in the database. Ciao. Vincent. -- Vincent Zweije <[EMAIL PROTECTED]> | "If you're flamed in a group you <http://www.xs4all.nl/~zweije/> | don't read, does anybody get burnt?" [Xhost should be taken out and shot] | -- Paul Tomblin on a.s.r.
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