On Tue, Oct 04, 2011 at 11:57:04AM +0200, Frederik Ramm wrote: > I tend to be against strict rules of any kind but when it comes to > the question of what exactly a complex relation means I think it > would be good to have one definition which every tool writer should > aspire to implement.
Mostly for historical reasons we have in OSM: * Nodes * Ways * Relations We could have done this differently. Only one kind of object class called "relation" would be enough: * Nodes could be written as relation with a lat and lon tag * Ways could be written as relation with just "node relations" as members We have other kinds of objects which are modelled as relations but could have their own object type: * Areas (multipolygon relations) * Routes * Turn restrictions All of them could have real OSM objects with their own ID space and strict definitions what goes inside them just like a way has the definition of having nodes as "members". I tend to think of a certain type of relations as a "semi-class". Its not a proper class like "node" and "way", but it is used in a similar way. First you look at the "type" tag of a relation to get the class, this gives you a special set of rules or restrictions on how to interpret the relation and its tags and members. Only then you look at the tags. So the *structure* (ie which members of what roles are allowed in what order) of a relation of a certain type should be pretty strict and solid, the *tags* is where we have the typical OSM flexibility. Jochen -- Jochen Topf [email protected] http://www.remote.org/jochen/ +49-721-388298 _______________________________________________ dev mailing list [email protected] http://lists.openstreetmap.org/listinfo/dev
