[Tagging] Reviving the conditions debate

Colin Smale colin.smale at xs4all.nl
Thu Jun 14 12:30:04 BST 2012


On 14/06/2012 13:00, Tobias Knerr wrote:
> On 14.06.2012 08:38, Colin Smale wrote:
>> My concern with this is that it may become unwieldy and cumbersome with
>> anything beyond fairly trivial cases such as your maxspeed example.
> For me, the goal is to make the common cases *easy*, and the rare
> complex cases *possible*.
Difficult to argue with that! The second part makes a flexible grammar 
essential, as you cannot predict what these rare complex cases might 
look like.
> It's far easier to build a visual editor if you only need to support a 
> limited subset of boolean logic. For example, the "filter" editor in 
> my mail client (Thunderbird) is limited to a subset of boolean logic 
> as well, for the same reason.
Sure, it's limited to match all/match any and a fixed list of operators. 
But Thunderbird is not trying to represent something in the physical 
world here, only to help the user.

> Here's a test case. No motor vehicles mon-fri between 1600-1800 except
> agricultural vehicles and good vehicles *in this direction*. Going the
> other way the sign is similar but the times are between 0600 and 0900.
>
> What would this look like using only AND operators?
> motor_vehicle:forward:(Mo-Fr 16:00-18:00) = agricultural
At first glance this looks like a motor vehicle going "forward" between 
those times is considered "agricultural". It doesn't feel very 
intuitive, based on the established key=value paradigm.

I thought of the following, based on the premise that the class 
"motor_vehicle" can be partially overridden by a subclass such as hgv or 
agricultural:
motor_vehicle=yes
motor_vehicle:forward:(Mo-Fr 16:00-18:00)=no
motor_vehicle:backward:(Mo-Fr 06:00-09:00)=no
hgv=yes
agricultural=yes

Colin




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