We probably don't need a true technical null value, you are right. But
if we introduce a formal method of defining defaults or implied values,
for example if highway=residential implies maxspeed=30 "unless tagged
otherwise", how can we tag "maxspeed is truly unknown, do not apply the
defaults"? Sure, we can use maxspeed=unknown, but then the value
"unknown" has the effect of NULL, i.e. a placeholder where a value could
be stored, but there is nothing there now. If we agree on using a
specific value like "none" or "unknown" or "NULL" for this function,
then defaults could possibly be applied in a broader, more defined way.
On 2016-01-24 11:12, Gerd Petermann wrote:
> I don't think so. Where do we need null values in OSM?
>
> As you said, maxspeed=none means something like maxspeed=unlimited.
>
> I can't think of any tag key which should be stored in OSM with a null value.
>
> In what case would that add valud information compared to having no such tag
> ?
>
> Gerd
>
> -------------------------
>
> VON: Colin Smale <colin.sm...@xs4all.nl>
> GESENDET: Sonntag, 24. Januar 2016 10:58
> AN: Tag discussion, strategy and related tools; Tijmen Stam
> BETREFF: Re: [Tagging] Removing name_1 and alt_name_1 from Wiki
>
> At present the string "none" is actually a value, the interpretation of which
> is specific to the key "maxspeed" . Maybe we should promote it to the
> equivalent of NULL in SQL.
>
> On 24 January 2016 10:43:16 CET, Tijmen Stam <mailingli...@iivq.net> wrote:
>
> With the value "none"
>
> For example on German Autobahnen, where you can drive as fast as you
> want is "maxspeed=none" which is different from having maxspeed not set:
> this means maxspeed is unknown or not tagged yet.
>
> On 20-01-16 09:06, Colin Smale wrote:
> Exactly.
>
> If a missing value (i.e. use the default) is not the same as explicitly
> having NO value, how do you override the default with "no value"?
>
> --colin
>
> On 2016-01-20 08:50, Gerd Petermann wrote:
>
> I don't think that the meaning really depends on the position. My
> understanding is that the
>
> complete value (e.g. "80||" ) is parsed by splitting it into separate
> strings at each pipe symbol.
>
> Result: three strings: "80" , "",""
>
> The value "|80|" also gives three strings: "","80",""
>
> Another point is that an empty value means "use the default", which can
>
> only make sense in special cases like this.
>
> Gerd
>
> -------------------------
>
> *Von:* Colin Smale <colin.sm...@xs4all.nl>
> *Gesendet:* Mittwoch, 20. Januar 2016 08:23
> *An:* Tag discussion, strategy and related tools
> *Betreff:* Re: [Tagging] Removing name_1 and alt_name_1 from Wiki
>
> I meant that there is a value missing "between the pipes", which at a
> slightly higher semantic level can mean "use the default". A
> definition which varies according to position doesn't feel well-formed
> to me.
>
> //colin
>
> On 2016-01-20 08:10, Gerd Petermann wrote:
>
> Colin Smale wrote
>
> The "lanes" tag family uses a different delimiter ("|"), sometimes
> together with a semicolon to make a kind of 2-d array. A
> double pipe
> ("||") indicates a missing value there. Wouldn't it be nice if
> we were
> consistent?
>
> That is new to me. My understanding of a double pipe is that
> described here:
> http://wiki.openstreetmap.org/wiki/Proposed_features/lanes_General_Extension#Default_values
>
>
> Proposed features/lanes General Extension - OpenStreetMap Wiki [1]
> wiki.openstreetmap.org
> A simple, straightforward extension of existing tags to specify properties
> not only for a way as whole but for the lanes of the way instead. Based on
> this general ...
>
> Proposed features/lanes General Extension - OpenStreetMap Wiki
> <http://wiki.openstreetmap.org/wiki/Proposed_features/lanes_General_Extension#Default_values>
> wiki.openstreetmap.org [2]
> A simple, straightforward extension of existing tags to specify
> properties not only for a way as whole but for the lanes of the
> way instead. Based on this general ...
>
> which indicates that a double pipe means one or two default values,
> depending on the position.
> At the end of the value, it means two default values.
>
> Gerd
>
> --
> View this message in context:
> http://gis.19327.n5.nabble.com/Removing-name-1-and-alt-name-1-from-Wiki-tp5864465p5865207.html
> <http://gis.19327.n5.nabble.com/Removing-name-1-and-alt-name-1-from-Wiki-tp5864465p5865207.html>
> Sent from the Tagging mailing list archive at Nabble.com [3].
>
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