Culture Geeks talk: "Adventures in Linked Data Land", by Richard Light. Feb, 25th 2009 - Regency Town House Culture Geeks is a Brighton-based community open to everyone who is interested in using digital technologies in the cultural sector.

1. Adventures in Linked Data Land
Richard Light Consultancy
Culture Geeks, 25 February 2009

2. Discovering Linked Data
Four principles of Linked Data (Tim B-L):
Use URIs to identify resources
●
Use HTTP URIs so that people can look them up
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Provide useful information about the resource
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Include links to other URIs in your data
●

3. Discovering dbPedia
Extraction of Linked Data from Wikipedia
●
Statements in info boxes (mainly) become RDF
●
triples:
<rdf:Description
rdf:about=quot;http://dbpedia.org/resource/Ber
lin_Marathonquot;>
<dbpprop:location
rdf:resource=quot;http://dbpedia.org/resource/
Berlinquot;/>
</rdf:Description>
Note the URLs

4. Browsing Linked Data
View RDF as a web page:
●
http://dbpedia.org/page/Berlin
Navigate from one data source to another
●
Specialist Linked Data browsers/plugins:
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DISCO
–
Marbles
–
Openlink Data Explorer
–
Tabulator
–

5. dbPedia page for Berlin

6. OpenLink Data Explorer: What

7. OpenLink Data Explorer: Where

8. Querying Linked Data
SPARQL query language:
●
http://www.w3.org/TR/2008/REC-rdf-sparql-query-
20080115/
And SPARQL XML results format:
●
http://www.w3.org/TR/rdf-sparql-XMLres/
“SPARQL end-points”:
●
http://dbpedia.org/sparql
http://dbtune.org/bbc/peel/sparql
http://data.linkedmdb.org/sparql

9. dbPedia SPARQL endpoint page

10. Asking interesting questions
German musicians born in Berlin:
●
●

11. So what do we have here?
An initiative to generate lots of Linked Data
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A Linked Data Cloud, containing a growing
●
number of RDF datasets
A hard-to-use query language capable of very
●
precise and powerful querying
Where do museums come into this picture?

12. The Wordsworth Trust
Typical museum collection: about 60,000 objects
●
Major collection of manuscripts (notebooks,
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letters, etc.)
Objects published to the Web from a ModesXML
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database
Unwise enough to allow me Remote Desktop
●
access ...

13. Typical collections object
GRMDC.C104.2

14. Same object represented as RDF

15. Same object represented as XTM

16. One identifier; three “views”
This object has a single persistent identifier:
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http://collections.wordsworth.org.uk/object/GRMDC.C104.2
This maps to different views depending on the
●
“Accept” header in the HTTP request:
application/rdf+xml >> RDF
–
application/xtm+xml >> XTM Topic Map
–
Otherwise >> HTML (human-readable)
–
Achieved through a custom 404 “page not found”
●
handler

17. “Page not found” handler (1)
All URLs are fictitious, so they generate a 404
●
Modified a generic smart 404 handler from:
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http://evolvedcode.net/content/code_smart404/
Added support for “303 See other” redirects
●
added wild card matching to re-format URLs
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18. “Page not found” handler (2)
Generic URL, plus requested Accept format,
●
determine initial “303 See other” mapping, e.g.:
http://collections.wordsworth.org.uk/object/GRMDC.C104.2
+
Accept: application/rdf+xml
=
http://collections.wordsworth.org.uk/object/rdf/GRMDC.C104.2
When this is passed back in, the 404 handler has to
●
generate the required RDF directly
Can't just keep redirecting requests!
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19. “Page not found” handler (3)
Redirect rules declare mappings:
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20. “Page not found” handler (4)
Generic URL plus a supported Accept type
●
generates a “303 See other” redirect
If it comes back as a page request, it is further
●
redirected with a “301 Moved permanently” to the
object's web page
If it comes back as an RDF or XTM request, the
●
record is fetched as XML and subjected to an
XSLT transform by the handler

21. What has been learnt?
The Linked Data paradigm encourages simple
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RDF triples: no “blank nodes”
For an object, this becomes a simple metadata set,
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very analogous to the PNDS DCAP format
The properties involved need to encapsulate the
●
whole relation between object and data, e.g.
<p:title>Ulswater from Pooley Bridge</p:title>
<p:technique>drawn</p:technique>
<p:maker>Farington, Joseph (1747-1821)</p:maker>
<p:technique>engraved</p:technique>
<p:maker>Middiman, Samuel (1750-1831)</p:maker>

22. Properties: which framework?
I have used dbPedia properties (for Linked Data
●
compatibility):
http://dbpedia.org/property/title
http://dbpedia.org/property/maker
A viable alternative would be PNDS DCAP:
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http://purl.org/dc/elements/1.1/title
http://purl.org/dc/elements/1.1/creator
One framework which doesn't fit is the CIDOC
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CRM:
E21 Physical Thing – E12 Production – E39 Actor = “creator”

23. The problem of URIs
Good Linked Data requires URIs everywhere
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Most of my museum RDF resolves to strings
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One exception is Geonames lookup:
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Ullswater
becomes
http://www.geonames.org/2635191/
In the absence of a central “people” registry,
●
should be minting URIs for people myself

24. Does it work? - yes, sort of

25. Data Explorer place view

26. Implementation details
HTML needed a “back link” to RDF to keep
●
OpenLink Explorer happy:
<link rel=quot;alternatequot; type=quot;application/rdf+xmlquot;
href=quot;http://collections.wordsworth.org.uk/object/data/GRMDC
.C104.2quot; title=quot;RDFquot; />
Result is totally unfindable: need a search or
●
harvesting mechanism:
– OAI support (possible)
– SPARQL end-point (harder)

27. Conclusions
Implementing an RDF Linked Data front-end to a
●
museum database is feasible if:
You can generate multiple outputs from your database
–
(XML is sufficient)
You can implement a suitable URL rewriter or 404
–
handler
It's easy (and a good idea) to mint and publish
●
URIs for your collection objects
It's less clear where all the other URIs we'll need
●
will come from

28. LD: foothills of the Semantic Web
Linked Data is a very modest start
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It's not obvious how this will scale
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Full Semantic Web will involve machine-driven
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processes
Judging by where we are today, that will be a
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while coming ...

29. Ask Multimap where Lancaster is

30. Get a Netbook delivered ...