ACTION-96 linking to related identifiers

Hi BP-editors

Here are some initial thoughts on the issues of linking from your own
Spatial Thing to other identifiers for the same thing or related things.

This action is to expand the text in section 7.2 of the BP draft that
currently says:

"it's useful to have hyperlinks to things like Geonames, wikipedia, OSM etc
(see list on the mailing list, keyword: stamp collecting)"

As per http://www.w3.org/DesignIssues/LinkedData.html item 4, it's useful
for people to link their data to other related data. In this context we're
most frequently talking about either Spatial Things and/or their geometry.

There are many useful sets of identifiers for spatial things and which ones
are most useful will depend on context.

I think there are two main challenges here - discovering relevant URIs that
you might want to connect to, deciding what is the nature of the
relationship between your original URI and potential link targets, and then
finding an existing vocabulary term that accurately reflects that
relationship.

As an example, let's take Edinburgh. In some recent work with the Scottish
Government, we have an identifier for the City of Edinburgh Council Area -
i.e. the geographical area that Edinburgh City Council is responsible for:

http://statistics.gov.scot/id/statistical-geography/S12000036

(note that this URI doesn't resolve yet but it will in the next couple of
months once the system goes properly live)

Here are some identifiers for Edinburgh and/or information about it that we
might want to link to, together with notes about how I found out about them.

http://statistics.data.gov.uk/id/statistical-geography/S12000036

My identifier is directly based on this one, but the Scottish Government
wanted the ability to create something dereferenceable, potentially with
additional or different info to the data.gov.uk one.  We're happy these two
are owl:sameAs

https://en.wikipedia.org/wiki/Edinburgh
Found by a google search for Edinburgh site:wikipedia.org).  This is a page
about a closely related but perhaps less specific concept of the place.
Possible document vs thing distinctions to be made here.  Possible
relationships: rdfs:seeAlso, schema:sameAs ? foaf:page?

http://dbpedia.org/resource/Edinburgh
I know the pattern for changing a wikipedia URI into a dbpedia one, so
found it that way.  Relationship: "more or less the same as" but not sure
I'd want to go as far as the strict semantics of owl:sameAs

http://data.ordnancesurvey.co.uk/id/50kGazetteer/81482 (Edinburgh)
Found by OS gazetteer search service for 'Edinburgh' then checking the
labels of the results that came up.  OS give it a type of 'NamedPlace' and
give it some coordinates.

http://data.ordnancesurvey.co.uk/id/50kGazetteer/81483 (Edinburgh airport)
Also found by the same OS gazetteer search service for 'Edinburgh'.  This
is clearly not the same as my original spatial thing, but I might want to
say something like 'within' or 'hasAirport'.

http://data.ordnancesurvey.co.uk/id/7000000000030505
Found by a search for 'Edinburgh' in the OS 'Boundary Line' service that
contains administrative and statistical geography areas in the UK.  The
first results of the search were parliamentary constituencies - had to
scroll down and look for one that had a stated rdf:type that matched what I
was looking for.  It's probably safe to say my identifier is owl:sameAs
this one.

http://sws.geonames.org/2650225/
Found with the Geonames search service:
http://api.geonames.org/search?name=Edinburgh&type=rdf&username=demo
Once you have found a place in geonames, there are other useful services to
find things that are nearby etc. Not sure exactly what this is, though it
has a RDF type of http://www.geonames.org/ontology#Feature

http://www.openstreetmap.org/relation/1920901  (administrative boundary)
machine readable data: http://www.openstreetmap.org/api/0.6/relation/1920901
Found via the search box at www.openstreetmap.org.
see also http://nominatim.openstreetmap.org/details.php?place_id=127903534
and http://www.openstreetmap.org/node/17898859 (node - somewhere around the
centre of Edinburgh)
I'm not sure of all the options with OSM - I'm sure others in the WG know
more -but it has identifiers for nodes, ways and relations, though it seems
that these identifiers tend to change quite frequently as the map is edited.

The outcome of this example is that it takes a bit of prior knowledge and
intelligent manual guesswork to find related URIs.  Some services, eg OS,
have useful search facilities, but the results may still need some
interpretation. Recommending some standard approach to providing a search
facility (or 'reconciliation API') for a collection of spatial data might
be a useful best practice.

Working out how to accurately describe the relationship is hard in general
and the BP document might be able to help by categorising some of the most
common relationships and perhaps suggest examples of appropriate matching
vocabulary terms.