On Sat, Aug 8, 2009 at 5:17 AM, Martin Koppenhoefer<dieterdre...@gmail.com> wrote: > why is this a value in the key: > maxspeed:wet=40 > couldn't you interpret "maxspeed:wet" as a key? The maxspeed in wet > condition? Could you explain the problem that arises (I am not an > informatics person and maybe for this don't understand these details > adhoc).
I gather that a value is something that can take an infinite number of values. e.g. A time can be 00:00:00.0, 00:00:00.01, etc. "Wet" is a weather condition. There are an infinite number of "weather conditions" - this may not be immediately obvious, but what would you answer if I asked you "how many weather conditions are there?" It is desirable to have a finite number of keys. That way, you can, for example, list all of the keys supported by OSM without having to use placeholders like maxspeed:<weather condition> or maxspeed:<time>. It also makes it easier for computer programs to use the keys - they can use a simple switch statement/table lookup on the key, then do any necessary parsing on the value field only. You could argue that you could explicitly support maxspeed:wet, but that makes about as much sense as supporting maxspeed[12:00-14:00] and not maxspeed[12:11-13:11] (i.e. not much). _______________________________________________ talk mailing list talk@openstreetmap.org http://lists.openstreetmap.org/listinfo/talk
