Using Linked Data - Linked Data: A Geographic Perspective - page 148

through the owl:sameAs predicate, also convey a very strong advantage on the
Linked Data Web: robustness. As with the traditional Web, there is no central point
of failure, and the decentralized approach means there is no administrative burden
of centralized organization required to assign unique URIs to each individual entity
(as well as the impossibility of defining to everyone's satisfaction exactly what the
entity is).
8.4.3 c orreSpondence betWeen i nStanceS : d ifference
If the information provided is the same but the things the two URIs are describing
are different, we need to be more careful than merely assigning an owl:sameAs
link. For example, GeoNames' “Southampton” (in the United Kingdom) and
Ordnance Survey's Administrative Geography's “Southampton” both have the same
name, but GeoNames refers to the City, a settlement, and Ordnance Survey refers
to the Unitary Authority Area. For certain purposes, these two could be considered
the same (if we were just interested in the general location of Southampton, say),
but for the specific context of local government, we might need to link more accu-
rately. While the GeoNames' Southampton (Settlement) does lie within the County
of Hampshire, Ordnance Survey's Unitary Authority Area is not an administrative
part of the County of Hampshire. Therefore, we need to specify the context in which
the two entities can be considered the same; see Section 8.8 for more details of how
to do this.
8.4.4 c orreSpondence betWeen i nStanceS : o ther r elationShipS
It is more usual, however, that there is some relationship other than similarity or
identity between two resources from different Linked Data sets. For example, the Isis
Tavern from Merea Maps' data sells Midnight Lightning Beer that comes from the
Best Beer dataset. Heath and Bizer (2011) refer to this as a relationship link . As with
the previous case, some relationships may only be valid in certain contexts of use.
8.4.5 e ncoding o utgoing l inkS
An outgoing, or external , link can be encoded using a triple where the subject of
the triple is in Merea Maps' dataset, and the object of the triple is located in another
dataset under a different namespace. The predicate may reside in Merea Maps'
namespace or in the third party's or alternatively come from yet another vocabulary.
The following example shows internal links from the URI for the Isis Tavern pub
in Merea Maps' data to other Merea Maps' data (line 7, in this case a literal) and
external links to Merean Mail's address data (line 8) and to GeoNames data (line 9):
1 @prefix rdf: < http://www.w3.org/1999/02/22-rdf-syntax-ns# >.
2 @prefix foaf: < http://xmlns.com/foaf/0.1/ >.
3 @prefix mm: < http://mereamaps.gov.me/placesOfInterest/ > .
4 @prefix postcodes: < http://mereamail.gov.me/addresses/ >.
5