[OSM-talk] Mappers and apps should focus on relations at the very start

[Fernando Trebien]

Interesting, I remember long ago trying to upload (by accident) a set
of relations with a cyclic dependency and receiving a server error.
Maybe the message was phrased in a misleading way but the error was
actually generated by JOSM. Will try again.

Dependency checking must be aware of cycles, otherwise it may end up
running an infinite loop. There are some other scenarios, such as
retrieving a relation's incomplete members, where a self-reference can
be problematic, but that's not the server's responsibility. I can't
imagine right now any scenario where self-references or cyclic
references woud be necessary to represent any information. (Not
suggesting the the server should implement that check.)

On Sat, Jun 27, 2015 at 9:03 PM, Paul Norman <penorman at mac.com> wrote:
> On 6/27/2015 1:14 PM, Fernando Trebien wrote:
>>
>> Actually no, the server checks for circular dependencies, and a
>> relation pointing to itself is a cycle. Try it, the server returns a
>> validation error.
>
> Nothing in the OSM data model prohibits a relation that references itself,
> or relations that form a cycle.
>
> As an example, see https://www.openstreetmap.org/relation/1368401 which
> contains itself twice. Longer cycles are also possible.
>
> I can't imagine a case where a cycle is sensible, and they are often
> difficult to delete, first requiring modifying the relations to remove the
> cycle, then deleting the relations.
>
>
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-- 
Fernando Trebien
+55 (51) 9962-5409

"Nullius in verba."