Copying the replies from the OSM Tagging Mailing list:
the OSM tag chain should be imho used only for very common things because each member
of the chain will turn up as a “top level” tag in the database and taginfo.
If used extensively for attributes I would consider it pollution of the database.
It is also much less flexible as you can specify only one attribute at a time.
Then François replied:
the OSM tag chain should be imho used only for very common things because
of the chain will turn up as a “top level” tag in the database and
We are using such chains in Power, Pipeline and Telecom groups. It works
power=transformer + transformer=distribution + voltage:primary=20000 +
man_made=street_cabinet + street_cabinet=telecom + telecom=exchange +
telecom:medium=copper + operator=Orange
Adding power: and telecom: prefixes would be seriously bad to encourage for
contribution and extremely redundant.
Furthermore, refining of well used tags often get discouraged because of
This doesn’t include the redundancy in namespaces’ prefixes which is worse.
If used extensively for attributes I would consider it pollution of the
It is also much less flexible as you can specify only one attribute at a
If you have to define more than one attribute with the same name it may be
the attribute isn’t well defined.
Have you examples please?
To which Sergio responded:
“Transformers” is a perfect example of “namespacing done backward”. Why “voltage:secondary=220”? In a correctly namespaced world it would be “secondary:voltage=220”.
*I understand that in spoken English you can say "the voltage of the *secondary *is *220 Volt", and that’s probably why those keys have been built with the terms in that particular order. (/BTW, logic and wording is very different in different cultures and languages. I think it wouldn’t had been in that order in, say, German: can a german speaker please confirm that?/)
Transformers can have and very often have more than one secondary: you have dealt with that using things like "voltage:tertiary=" and the likes (windings:tertiary=, I suppose…). And what if the transformer has 3 secondaries? Or 4?
Isn’t “secondary:1:voltage=200” better? Don’t you see that’s more logical and expandable? Don’t you see that here we assign a quantity (220) to something that has the correct dimensions (voltage), like in the previously globally defined key "voltage="? Don’t you see how with that syntax everything related to the first (/second, third, fourth,… nth/) secondary (/wingdings, current, whatever…/) would be grouped under "secondary:n:="?
And if transformers weren’t meant to be a “/namespaced thing/”, why using the columns? Why not voltage_secondary= ?*
Don’t you see that with the transformers a new first level keyword, "rating=" have been implicitly defined and documented in the transformers page and how that keyword can be useful in other contexts… or namespaces, if you prefer?*
BTW, what is that telecom:medium=copper thing (https://wiki.openstreetmap.org/wiki/Key:telecom:medium)? /“Telecoms” /do not have a medium: local loops have. Is that meant to be a namespaced thing? Have this being debated/approved? I have seen it applied to buildings: what is the meaning of that?
Adding power: and telecom: prefixes would be seriously bad to encourage for contribution and extremely redundant.
To the contrary! Please read in the forum my rationale explaining exactly how that would be beneficial…