[Tagging] Discussion about Multivalued Keys

Colin Smale colin.smale at xs4all.nl
Wed Jan 27 22:22:33 UTC 2016


On 2016-01-27 22:54, moltonel 3x Combo wrote:

> On 27/01/2016, Colin Smale <colin.smale at xs4all.nl> wrote: 
> 
>> One way, using a "subscript syntax" with a "data structure" construct
>> using a "." as a separator":
>> lane[1].destination=Paris
>> lane[2].destination[1]=Rome
>> lane[2].destination[2]=Milan
>> lane[3].destination[1]=Berlin
>> lane[3].destination[2]=Munich
>> 
>> Alternatively, using a "suffix syntax", something like you suggest
>> lane_1:destination=Paris
>> lane_2:destination_1=Rome
>> lane_2:destination_2=Milan
>> etc.
>> 
>> Thirdly, using the "seamark" construction:
>> lane:1:destination:1=Paris
>> lane:2:destination:1=Rome
>> lane:2:destination:2=Milan
>> etc.
> 
> Concerning foo_1 vs foo[1] vs foo:1, I this the last one can be safely
> thrown to the idea bin (despite being used by seamarks) because ':'
> clashes with namespacing, which is firmly established. foo[1] looks
> better than foo_1 to my programer eyes, but is has no technical
> advantage (?) and I suspect that most people will find foo_1 more
> pleasing, it's also one less character to type, less annoying to parse
> with a regexp, and much more established in taginfo.

Would you feel any different about your foo:1 example if it were written
foo%1, avoiding any clash with namespacing? 

By the way, I am trying to maintain the distinction between the "suffix
notation" where the index value is actually the final part of the key
segment, and the "hierarchical/seamark" notation where the index value
is a separate segment of the full key string. 

Maybe we should look at some technical use cases, like "in a navigation
map creator, find all the categories for a POI" or "find the per-lane
destination (and destination:ref and turn-lane stuff) information so I
can construct a simulated road sign". Some will be done with a
programming language, others may naturally tend towards SQL. 

> Concerning using '.' as a separator instead of ':', I don; t see what
> it brings us, beside familiarity to users of some programing languages
> (but change language and sudenly ':' becomes more familiar).

Sometimes using a familiar character (such as the ":" here) with new
semantics can lead to confusion. There comes a point when it is better
to make a clean break so there is no confusion. Whether it is a colon or
a dot or some other character is "detail" really. 
  
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