Database Reference
In-Depth Information
Trust measurement is a very open area of research, and there are not yet any sat-
isfactory automatic and general solutions to the problem. The best advice we can
give at present, when evaluating a third-party Linked Data set for potential reuse,
is to manually consider the provenance metadata and use your best judgment. We
discuss more about how to assess the provenance of other people's data in Chapter 8
on Linking Data.
7.9 LICENSING LINKED DATA
According to Bizer, Jentzsch, and Cyganiak (2011), 85% of Linked Data does not
include any licensing information. Specifying the terms under which the data can
be reused helps encourage its reuse as it reduces uncertainty about what is allowed.
Hence, it is good practice to include information about the licensing restrictions on
any Linked Data that you publish within its metadata or, if there are no restrictions,
as encouraged in the Linked Open Data movement, to include a waiver statement.
You should specify your license in RDF (and there are many licenses already
available that you can reuse, discussed in a separate section) and then indicate
where your license file is to be found by including a triple in your dataset with the
predicate
dcterms:license
.
7.9.1
o
pen
l
InkeD
D
ata
The definition of
open
content or data is that “anyone is free to use, reuse, and redis-
tribute it—subject only, at most, to the requirement to attribute and share-alike.”
39
Tim Berners-Lee has a five-star rating system for the openness of Linked Data, and
it is interesting to note that he places more emphasis on the openness of the data than
on the ease of linking. The rating system (Berners-Lee, 2006) is as follows:
★
Available on the web (whatever format)
but with an open licence, to be Open Data
★★
Available as machine-readable structured data (e.g., excel instead of image scan of a table)
★★★
as (2) plus non-proprietary format (e.g., CSV instead of excel)
★★★★
All the above, plus: Use open standards from W3C (RDF and SPARQL) to identify things,
so that people can point at your stuff
★★★★★
All the above, plus: Link your data to other people's data to provide context
7.9.2
l
InkeD
D
ata
l
IcenSeS
The Creative Commons
40
is a frequently used licensing framework for the World
Wide Web that offers several licensing options, including allowing or preventing
commercial use, modification, and attribution of the work. A license can be encoded
in RDF using the Creative Commons Rights Expression Language, which is speci-
fied under the namespace <
http://creativecommons.org/ns#
> and then referred to in
the Linked Data set using the triple (shown in Turtle format)
41
:
@prefix cc: <
http://creativecommons.org/ns#
>
.
cc:license <
http://creativecommons.org/licenses/by-sa/3.0/rdf
>.
