[OSM-talk] keys

[Etienne]

On 6/12/06, Immanuel Scholz <immanuel.scholz at gmx.de> wrote:
>
> Hi,
>
> > I think the users (us) are finding that the lack of any structure is
> > becoming a bit of a problem. See previous discussions about UK centric
> > schemes, highway=autobahn, etc.  I think this initiative is not about
> some
> > complex programming changes but more about the users doing some
> > self-organising using the tools they have already got.  I really like
> the
> > lack of any *enforced* structure, but I also see that there are benefits
>
> > to several users sharing a common scheme - that is all that is
> happening.
> >
>
>
> > > But: Some of your ideas were thought before ;-).
> > Where?
>
> The usual channels. Mailing list, wiki, IRC.. I mean - coders already
> thought about possible needs of organizing the keys a bit.
>
>
> >> To have a "registry", where some metainformation about the data is
> stored
> >> was part of the key/value design from beginning. The idea was that
> >> keywords can have keywords and so clients are able to read out these
> >> keywords and interprete them by themself.
> >
> > Can you give an example? I don't understand what you mean by "keywords
> can
> > have keywords".
>
> Currently, only Nodes, Segments, Ways (and Areas) are "first class
> objects", which mean, you can attach key/values only to this.
>
> It was an original idea to give the user the possibility to attach
> key/values to Keys. (Ok, the REALLY original idea was only to have
> 'keywords' and to be able to attach keywords to keywords. But it comes up
> to the same).
>
> Having this, a user can attach for example the key/value
> "possible_values=major,minor,highway" to "class". An other example is to
> attach "class_icon=http://foo.bar/baz.jpg" to the key "church"


This is already being done, here:
http://wiki.openstreetmap.org/index.php/Osm-map-features.xml

Here's an example of how a church is associate with the icon that is used to
represent it:

  <rule k="amenity" v="place_of_worship">
    <symbol xlink:href="#church" width='5' height='10' x-offset='-5'
y-offset='-10'/>
  </rule>

   ...

  <svg:symbol id="church"
     viewBox="0 0 5 10"
     fill='#000000'>
      <svg:path d="M 0 10 L 0 5 L 5 5 L 5 10 z M 0 2 L 5 2 L 5 3 L 0 3
z M 2 0 L 2 5 L 3 5 L 3 0 z" />

  </svg:symbol>

Could JOSM parse the <rule> tags in this file and use it to give the user a
set of possible values for the keys in the Map Features scheme?


A client can then read out this values and decide to pre-fill a combobox
> which selects from a "class" with the values "major", "minor" and
> "highway". Futher, the client could display the URL for every node which
> has the class=church.
>
>
> To summarize, the "key/values for keys" is just a simple way of using
> existing API's to implement a *distribution* of ontology. It is not better
> in actually defining that ontology than any other scheme you can quickly
> come up with ;-).
>
>
>
>
> Some things to keep in mind:
>
> - You will never have *no* misinterpretation. I strongly suggest than you
> do not make applications that depend on "no wrong data" to work except:
> - If you really make an application that has to enforce some scheme (e.g.
> routing applications), then you should always add a proxy which filter out
> and preprocess your data (as gpsdrive does).


Ciao, Imi
>
>
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