[Tagging] Reviving the conditions debate

Colin Smale colin.smale at xs4all.nl
Wed Jun 13 17:11:53 BST 2012

For some reason everyone seems determined to come up with the most 
complex system imaginable, instead of taking successful ideas from the 
rest of the world. This trait is what causes many projects to fail. 
Let's not look at this as simply a discussion about "access tags", but 
an opportunity to extend the syntax of the current key-value pair system 
to include flexible extensibility.

How about something like access:expr=expression, where the expression is 
in some simple syntax and can reference pseudo-variables like time, day, 
weather, weight, height etc. Why not use a javascript-compatible syntax? 
Or a bit of XML? No point in re-inventing the wheel.


On 13/06/2012 14:35, Eckhart Wörner wrote:
> Hi everybody,
> I want to revive the discussion on how to tag restrictions that depend on certain conditions. My idea is to finalize the proposal described in http://wiki.openstreetmap.org/wiki/Proposed_features/Extended_conditions_for_access_tags and finally accept it.
> The reasons for picking this proposal:
> * The proposal mostly describes syntax that is already used for tagging, e.g. a maxspeed in a certain direction is almost always tagged as maxspeed:forward, maxspeed:backward
> * The proposal is intuitive and simple to use: the key of a tag is the base tag + a set of conditions that all have to be true for the key to apply (i.e. logical AND).
> * The proposal is complete: every logical formula of conditions can be expressed in it (technically, it's pretty similar to disjunctive normal form).
> * The proposal is consise: it follows the pattern most dominant with road restrictions, namely overriding general restrictions with special restrictions. It normally uses no more than one tag per sign.
> * The proposal is extensible: the set of conditions is not fixed and can be extended to new conditions. It is possible to set a sane default for new conditions that are experimental.
> * The proposal is easily implementable: I implemented it in a prototype already.
> The only real negative aspect that has been mentioned until now:
> * the proposal puts a lot of information into keys and theoretically allows for an unlimited set of keys. (The reality however shows that those keys tend to be the same, e.g. taginfo shows no less than 335 elements with key "maxspeed:(22:00-06:00)").
> Competing proposals:
> * http://wiki.openstreetmap.org/wiki/Proposed_features/access_restrictions_1.5 - in my opinion a horrible and incomprehensible syntax with arbitrary distinctions, taginfo revealed almost no uses (for example, "maxspeed:hgv:wet" in the Extended Conditions proposal above is "access:lgv?wet.speed" in the Access Restrictions 1.5 proposal)
> Opinions?
> Eckhart
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