[OSM-dev] Datamodel relation/member constraints

[Robert Vollmert]

On May 30, 2008, at 23:18, Thomas Wood wrote:

> On Fri, May 30, 2008 at 9:21 PM, Stefan de Konink  
> <skinkie at xs4all.nl> wrote:
>> So would it be allowed to do:
>>
>> type=node ref=1 role=from
>> type=node ref=2 role=at
>> type=node ref=1 role=at
>> type=node ref=3 role=to
>>
>> Or is the second 1 not allowed?
>>
> If by ref you mean node id, then yes, the second 1 is not allowed.
> The API used to throw an unhandled exception back at you (500) if you
> did it because of an index constraint on the database.
> This has recently been fixed to actually return a nice error and stop
> corrupting the database. (Although it may not have been deployed yet)

I'd hoped we only require the triple type/ref/role to occur at most  
once in a relation -- I'm sure there's some situations where one  
object logically fills two different roles in a relation.

Examples: Modelling a u-turn-restriction with from,at,to roles, in  
which case from and to might be the same object. Start and End nodes  
in circular routes.

Cheers
Robert