osmway:node/osmway:node redundancy

[1ec5]

With the --add-way-node-order flag, osm2rdf includes osmway:node triples that in turn include osmway:node triples, but these are two distinct uses of the osmway:node predicate that have objects of different types. The osmway:node of a way isn’t really a node per se. If you write something like ?way osmway:node ?node . ?node osmway:node, the UI suggests ?node as the next token, which is guaranteed to return zero results.

Should ways have osmway:member triples for consistency with osmrel:member, since the objects in both cases are structured similarly? Or maybe the predicate could be osmway:vertex, based on the terminology occasionally used by OSM editors?

[patrickbr]

I agree, the current situation is (for historical reasons) very confusing and inconsistent.

We have created a PR to fix this, please feel free to test it and give some feedback :)

[hannahbast]

@1ec5 The latest version of https://qlever.cs.uni-freiburg.de/osm-planet now has better names for these. Here is an example query, which showcases them. We thought about the right names quite a bit and we like them. They are meaningful and match the terminology used in the OSM world. Do you also like them?

PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX osmway: <https://www.openstreetmap.org/way/>
PREFIX osmrel: <https://www.openstreetmap.org/relation/>
SELECT ?member_id ?member_pos ?node_id ?node_pos ?geometry WHERE {
  osmrel:51477 osmrel:member_ref ?member_ref .
  ?member_ref osmrel:member_id ?member_id .
  ?member_ref osmrel:member_role "outer" .
  ?member_ref osmrel:member_pos ?member_pos .
  ?member_id osmway:node_ref ?node_ref .
  ?node_ref osmway:node_id ?node_id .
  ?node_ref osmway:node_pos ?node_pos .
  ?node_id geo:hasGeometry/geo:asWKT ?geometry .
}
ORDER BY ?member_pos ?node_pos

https://qlever.cs.uni-freiburg.de/osm-planet/rXMxZn

[patrickbr]

@hannahbast, there has been some discussion in the corresponding PR since last week and we have currently settled on the following schema:

osmrel:51477 osmrel:member ?member .
?member osmrel:member_role ?member_role .
?member osmrel:member_pos ?member_pos .
?member osmrel:member_id ?memer_id .

osmway:100 osmway:member ?member .
?member osmway:member_id ?member_id .
?member osmway:member_pos ?member_pos .

In particular, note the comment by @1ec5 who had some great remarks regarding our previous concept.

TLDR:

“Ref” is somewhat confusing because ref=* is a very common key on both relations and ways. If you renamed member only for consistency with osmway:node_ref, I’d suggest calling the latter osmway:member instead, to avoid the need for this _ref suffix. This is how OverpassQL refers to the concept.