[Tagging] Benefits of namespaces

Paul Allen pla16021 at gmail.com
Mon Dec 17 12:01:32 UTC 2018


On Mon, Dec 17, 2018 at 1:25 AM Fran├žois Lacombe <fl.infosreseaux at gmail.com>
wrote:

>
> I still think that actuator=* is better than two pipeline:valve:actuator=*
> and railway:switch:actuator=* because the first is really more concise and
> reusable between valves and railway switches.
> Like I don't like fire_hydrant:position instead of simpler location=*.
>
> Can someone brings benefits from using namespaces in this particular
> situation please?
>

There is a benefit to the authors of editors such as iD and JOSM when the
set of values for the two
different use cases is not identical.  So if valve actuators take the
values A, B, and C, whilst
railway actuators take the values A, X,  and Y, this causes code complexity.

The reason is that a key like pipeline:valve:actuator can be handled as a
list of values A, B, C
and a key like railway:switch:actuator can be handled as a list of values
A, X and Y.  But if it's
just actuator=* for both then the editor needs extra code to present
whichever values are valid
for the appropriate primary key.  It's not much for any one key, but it
starts to add up when there
are several keys like that.  Alternatively the editor just presents a list
of A, B, C, X and Y in both
cases and then people end up accidentally using values that are
inappropriate simply
because they're in the list.

Even if the values are of one are a subset of the other, it means that
extra code is needed to
distinguish between the two primary keys to decide whether to present a
limited list or a full
list of values.  Throw in potential complications with associated keys that
may differ between
the two types of actuator (do railway actuators have "turn to open"?) then
the code can get
messy.

This isn't theoretical speculation.  The author of iD has, in the past,
expressed unhappiness
about such re-usability.

I'd also guess that such re-use also causes similar problems on the carto
side if, for example,
railway actuators get different rendering from pipeline actuators.

Although my first instinct would be to minimize the number of keys in the
database that turns
out to be a premature optimization.

-- 
Paul
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