[OSM-talk] Proposal superseded_by tag for ID stabilisation

[Gregor Horvath]

Hi,

I have thought through this again and think we should keep it simple and
stupid (KISS):

Am Wed, 3 Aug 2011 20:36:38 +0200
schrieb Gregor Horvath <gregor at ediwo.com>:

> ** splitting of ways (old ID would then point to only half)
>    A split to A,B:
>      A.superseded_by = B
>      A does not get deleted

In this case A does not get deleted. It alters it's meaning because the
old ID points only to the half. But that is not different to adding or
editing a tag of that ID. This can also change the meaning of the ID.

I think it is not possible to manage a change history of ID meanings.

All we can do is  provide a replacement ID when an ID is deleted. This
can not be an exact replacement, just a hint.

Therefore a rule of thumb is this tag can only be applied to deleted
IDs.

> ** merging (old ID would become invalid in 50% of cases)
>    - example 1: Relations for long-distance routes created in several
>                 places until they "meet", and are merged, with one of
>                 them being deleted.
>    - example 2: a POI node might later be joined to be part of an area
>                 representing a shop;  this shop area might later be
>                 joined to others to represent an entire building that
>                 contains several shops 
> 
>    A,B gets merged to A: 
>      A.superseded_by = B
>      B deleted (visible=false)
>      B.superseded_by = A

same here: A does not get the tag, because it is not deleted.

> 
> ** supersede multiple objects (a merge operation) 
>    A,B,C  gets replaced by C
>      A.superseded_by = C
>      B.superseded_by = C
>      C.superseded_by = A
>      C.superseded_by = B
>      A,B deleted (invisible)

same here C does not get the tag, because it is not deleted.

--
Greg