This document provides an introduction to linked open data for museums. It discusses limitations of keyword searching, defines linked open data and its core principles. It also covers topics such as copyright and licensing, the RDF data model, triples, questions answered by RDF, core vocabularies, ontologies, finding links between data, embedding schema.org metadata, and managing linked open data. Exercises are provided to help readers practice converting data to RDF triples and linking data to external vocabularies.

1. An Introduction to
Linked Open Data for Museums
David Henry
Jarred Moore
MW2014
Presented by

2. An Introduction to Linked Open Data for
Museums

3. Limitations of Keyword Searching
Polysemy: One word with multiple meanings. E.g.
man
crane
bank
Synonymy: Multiple words with the same meaning.
buy OR purchase
create OR make
eliminate OR remove OR abolish
Signal to noise ratio e.g.
Try searching for the term
“Mississippi”

4. What is Linked Open Data?
On the web, open license
Machine-readable data
Non-proprietary format
RDF Format
Linked RDF

5. Copyright and Licensing
If Your content files are still under copyright and your institution is the
copyright owner, encourage your institution to license the content as
openly as possible
CCO
CC-BY
CC-BY-SA
CC-BY-NC

6. What is RDF?
• “Resource Description Framework (RDF) is a standard model for data
interchange on the Web. RDF has features that facilitate data merging
even if the underlying schemas differ, and it specifically supports the
evolution of schemas over time without requiring all the data
consumers to be changed. “ (from W3C)
• “…making Statements about resources (in particular web resources)
in the form of subject-predicate-object expressions.” (Wikipedia)

7. What are Triples?
• Triples are statements of fact (or assertions) composed of a
subject, predicate, and object. For example:
“David Henry”
Subject
“Lives in”
Predicate
“St. Louis”
Object

8. What are Questions Answered by RDF?
Fact-Based
Interpretive
Theoretical
Subjective
Analytical

9. Fact Based Questions ask Who, What,
When Where (Not so much Why)
Fact-Based
Questions
Who directed “Citizen Kane’?
What’s a daguerreotype?
Where did Van Gogh paint ‘Starry Night’?

10. Fact Based Question:
Are there any daguerreotypes of the
Mississippian mounds in St. Louis, Missouri?
Title: Group of people standing on a partially destroyed Big
Mound.
Description: Group of people standing on a partially destroyed Big
Mound.
Place: St. Louis, Missouri
Dates: 1869
Type(s): photo, Daguerreotype
Maker/Creator: Thomas M. Easterly
Subjects: Mississippian Culture, mounds
Identifier: PHO:17665
Permalink: http://collections.mohistory.org/resource/9952

11. Triples to Complex
Graphs
Thomas M. Easterly
1869Subject
“Mississippian Culture”
hasSubject
hasLabel
hasType
Daguerreotype

12. “Thomas M.
Easterly” Name: Thomas M. Easterly
Birth Date: October 3, 1809
Death Date: March 12, 1882
Places of Residence:
Guilford, Vermont
Liberty, Missouri
St. Louis, Missouri
Bio: Thomas M. Easterly was one of the leading
American Daguerreotypists ….
During the 1860s, improvements in photographic development
caused daguerreotypes to become out of fashion. Easterly refused
to acknowledge these changes believing the highly detailed
daguerreotypes were far superior in terms of beauty or
permanence urging the public to "save your old daguerreotypes for
you will never see their like again".

13. Exercise 1.
Time: 10-15 minutes Activity:
• Break into groups of 2-3.
• Write out one or more research questions.
• For each question, draw a entity-relationship graph
that could provide an answer to the question

14. What’s Wrong with the Good Ole Web?

15. What is a Uniform Resource Identifier?
Uniform
Resource
Locator
-----
Purpose:
To locate a
web resource
(document)
Uniform
Resource
Name
-----
Purpose:
To identify
any resourceIn Linked Open Data,
URIs act as both URLs and URNs
UR
I

16. Principles of Linked Data
• Use URIs to denote things.
• Use HTTP URIs so that these things can be referred to and
looked up ("dereferenced") by people and user agents.
• Provide useful information about the thing when its URI is
dereferenced, leveraging standards such as RDF, SPARQL.
• Include links to other related things (using their URIs) when
publishing data on the Web.
To make this happen subjects and predicates MUST be defined
by URIs. Objects may be URIs or literals.

17. Triples to Complex
Graphs
Resource:9952
Thomas M. Easterly
1839
ns1:Subject_91011
“Mississippian Culture”
nso:hasSubject
nso:hasLabel
nso:hasType
“Daguerreotype”
ns1:type_80345
Resource:92142

18. Triples to Complex
Graphs
http://collections.mohistory.org/resource/9952
ns1:Person_5678
Thomas M. Easterly
1839
ns1:Subject_91011
“Mississippian Culture”
nso:hasSubject
nso:hasLabel
nso:hasType
“Daguerreotype”
ns1:type_80345

19. What two words are most commonly
found in a browser window?
Web links have a half life of about ten years.
In other words, 50% of links that are 10 years
old are broken.

20. Document
DocumentDocument
DocumentDocument
Link rot is a serious problem on the document-based web.

21. Person
PersonObject
PlaceObject
createdBy
createdBy
knows
livesAt
Link rot is even more serious on the web of data.

22. Rules for persistent URI’sCoolURI’s
• No date Context
• No ownership context
• No technology context
• Re-use existing identifiers
• Link multiple representations
• Implement 303 redirects for
real world objects
NotCoolURI’s
• Avoid stating ownership
• Avoid version numbers
• Avoid query strings
• Avoid file extensions

23. Example URI:
http://education.data.gov.uk/ministryofeducation/id/school/123456
http://education.data.gov.uk/doc/school/v01/123456
states ownership
version number
good
Mostly good
http://www.example.com/id/alice_brown
http://data.nytimes.com/88843902954064461461

24. Writing RDF
RDFXML
Turtle
NTriples
<rdf:RDF xmlns:ns0=“http://mydomain.org/people/”
xmlns:n1=http://otherdonain.org/>
<description about=“ns0:David_Henry”>
<ns1:livesIn>St. Louis, MO</ns1:livesIn>
</description>
@prefix ns0: <http://mydomain.org/people/> .
@prefix ns1: <http://otherdomain.org/> .
ns0:David_Henry ns1:livesIn “St. Louis, MO” .
<http://mydomain.org/people/David_Henry> <http://otherdomain.org/livesIn> “St. Louis, MO” .
“David Henry” “Lives In” “St. Louis”

25. Triples to Complex
Graphs
http://collections.mohistory.org/resource/9952
Resource:92142
Thomas M. Easterly
1839
ns1:Subject_91011
“Mississippian Culture”
nso:hasSubject
nso:hasLabel
nso:hasType
“Daguerreotype”
ns1:type_80345

26. Graph to RDF as Turtle
@prefix resource: <http://collections.mohistory.org/resource/> .
@prefix ns0: <http://collections.mohistory.org/vocab/relators/> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema> .
resource:9952 ns0:dateCreated "1869-01-01"^^xsd:date .
resource:9952 ns0:hasType <http://collections.mohistory.org/vocab/daguerreotype> .
resource:9952 ns0:createdBy resource:92142 .
resource:92142 ns0:hasLabel "Thomas M. Easterly" .
resource:9952 ns0:hasSubject resource:5215 .
resource:5215 ns0:hasLabel "Mississippian Culture" .

27. Exercise 2.
Time: 15 minutes Activity:
• Break into groups of 2-3.
• Using the graph defined in Exercise 1, define a set of
triples from the graph (Use your own URIs)
• Use the RDF validator at
http://www.rdfabout.com/demo/validator/

28. What is Linked Open Data?
On the web, open license
Machine-readable data
Non-proprietary format
RDF Format
Linked RDF

29. Principles of Linked Data
• Use URIs to denote things.
• Use HTTP URIs so that these things can be referred to and looked up
("dereferenced") by people and user agents.
• Provide useful information about the thing when its URI is
dereferenced, leveraging standards such as RDF, SPARQL.
• Include links to other related things (using their URIs) when
publishing data on the Web.

32. Core Vocabularies
• RDF & RDFS
• Useful terms: rdf:type, rdfs:label
• SKOS (Simple Knowledge Organization Schema)
• Useful terms: skos:broader, skos:narrower
• OWL (Web Ontology Language)
• Useful terms: owl:sameAs, owl:differentFrom
• Dublin Core
• Useful terms: dc:creator, dc:date, dc: subject
• Foaf
• Useful terms: foaf:name, foaf:knows, foaf:image

33. Ontology
Thesaurus
Controlled
Vocabulary
Vocabulary Types
Simple list of terms.
e.g. DCMI Types list
Hierarchical list of terms
e.g. Library of Congress Subjects
Hierarchical list of terms with
relationship constraints
e.g. CIDOC CRM

34. Example using CRM
Core
E52 Time-Span
1898
E53 Place
France
(nation)
E21 Person
Rodin Auguste
E52 Time-Span
1840
E67 Birth
Rodin’s birth
E52 Time-Span
1917
P4 has
time-span
E69 Death
Rodin’s death
E12 Production
Rodin making “Monument
to Balzac” in 1898
E21 Person
Honoré de Balzac
E55 Type
sculptors
E84 Information Carrier
The “Monument to Balzac”
(plaster)
E55 Type
plaster
E52 Time-Span
1925
E55 Type
bronze
E40 Legal Body
Rudier (Vve Alexis)
et Fils
E12 Production
Bronze
casting“Monument to
Balzac” in 1925
E55 Type
companies
E84 Information Carrier
The “Monument to
Balzac”(S1296)
P108B was
produced by
P62 depicts
P16B was used for
P134 continued
P2 has type
P120B occurs
after
P4 has time-span
P2 has type
P100B died in
P98B was born
P4 has time
-span
P2 has type
P14 carried out by
P14 carried out by
P62 depicts
P108B was
produced by P2 has type
P7 took
place at
P4 has time-span

35. Implementing Linked Open
Data
Link existing data
• Low barrier to entry
• Controlled lists and
thesauri
• Not very descriptive
Manage data to fit an ontology
• High barrier to entry
• Ontologies
• Very descriptive
RDF facilitates the “evolution of schemas over time”

36. What is RDF?
• “Resource Description Framework (RDF) is a standard model for data
interchange on the Web. RDF has features that facilitate data merging
even if the underlying schemas differ, and it specifically supports the
evolution of schemas over time without requiring all the data
consumers to be changed. “ (from W3C)
• “…making Statements about resources (in particular web resources)
in the form of subject-predicate-object expressions.” (Wikipedia)

37. Triples to Complex
Graphs
http://collections.mohistory.org/resource/9952
Resource:92142
Thomas M. Easterly
1839
ns1:Subject_91011
“Mississippian Culture”
nso:hasSubject
nso:hasLabel
nso:hasType
“Daguerreotype”
ns1:type_80345

38. Finding Links
• Linked Open Vocabularies is a good starting point
• Other well-used sources include:
• DBPedia - for a wide-range of types (people, places, subjects,
concepts)
• Id.loc.gov – for name authorities and subjects
• Viaf.org – for name authorities
• geonames.org – for geographic locations
Problem: There are no universal vocabularies

39. A Note of Caution
When re-using existing URIs, be sure to use the URI that represents
the entity (thing/concept/person) and not the web resource.
For example:
http://id.loc.gov/authorities/subjects/sh85126887.html
Is NOT the same as:
http://id.loc.gov/authorities/subjects/sh85126887

40. A Note of Caution
When re-using existing URIs, be sure to use the URI that represents
the entity (thing/concept/person) and not the web resource.

41. Finding Links
• Matching predicates.
• hasType => rdfs:type, dcterms:type, crm:E55_Type
• createdBy => dc:creator, crm:P94i_was_created_by
• dateCreated => dc:created, ?
• Matching value vocabularies.
• “Daguerreotype” => http://dbpedia.org/resource/Daguerreotype
• “Mississippian Culture” => http://id.loc.gov/authorities/subjects/sh85086218
• “Thomas Easterly” => http://viaf.org/viaf/13114715/
Problem: There are no universal vocabularies

42. Triples to Complex
Graphs
http://collections.mohistory.org/resource/9952
Resource:92142
Thomas M. Easterly
1839
ns1:Subject_91011
“Mississippian Culture”
dc:subject
rdfs:label
rdf:type
“Daguerreotype”
ns1:type_80345

43. @prefix resource: <http://collections.mohistory.org/resource/> .
@prefix ns0: <http://collections.mohistory.org/vocab/relators/> .
@prefix dc: <http://purl.org/dc/terms/> . # dc:creator; dc:created; dc:subject
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . # rdf:type
@prefix owl: <http://www.w3.org/2002/07/owl#> . # sameAs; differentFrom
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> . # date; integer
resource:9952 ns0:dateCreated "1869"^^xsd:date .
resource:9952 dc:date "1869-01-01"^^xsd:date .
resource:9952 ns0:hasType <http://collections.mohistory.org/vocab/daguerreotype> .
resource:9952 rdf:type <http://dbpedia.org/resource/Daguerreotype> .
resource:9952 ns0:createdBy resource:92142 .
resource:9952 dc:creator <http://viaf.org/viaf/13114715/> .
resource:92142 ns0:hasLabel "Thomas M. Easterly" .
resource:9952 ns0:hasSubject resource:5215 .
resource:9952 dc:subject <http://id.loc.gov/authorities/subjects/sh85086218> .
#resource:5215 ns0:hasLabel "Mississippian Culture" .
resource:92142 owl:sameAs <http://viaf.org/viaf/13114715/> .
Graph to RDF as Turtle

44. Exercise 3.
Time: 15-20 minutes
Activity:
• Break into groups of 2-3.
• Using the triples you defined in Exercise 3, find existing URIs
to link with your local URIs.
• Be prepared to explain why you chose the URIs your chose.

45. How Tos
• Embed schema.org data in a web page
• Publish static RDF files
• Manage local vocabularies and align them with existing vocabularies
• Contributing to a collection aggregator – e.g. Europeana or DPLA
• Publish existing database records as RDF
• Managing RDF data in a triple (or quad) store

46. Embedding
schema.org
<div itemscope itemtype="http://schema.org/CreativeWork">
<img src="http://collections.mohistory.org/resource/16679.jpg" class="item_image"
width="300" itemprop="image" />
<div id="record_detail">
<p><b>Title:</b> <span itemprop="name“>Lord Fitzwilliam and manservant, hunting
on the Hunt Farm on Gravois Road.</span></p>
<p><b>Description:</b> <span itemprop="description"></span></p>
<p><b>Item:</b> <span itemprop="additionalType">Daguerreotype</span></p>
<p><b>Dates:</b> <span itemprop="dateCreated">1855 to 1865</span></p> .
Copy and paste entire text

47. Publish static RDF files
• RDF files can be hand-written (what fun!) or rendered using templates
• Paths to RDF files can be submitted to RDF search engines such as
Sindice (http://sindice.com)
• Caution: Some content negotiation would be required.
• Remember: http://mydomain.org/resource/1234.rdf is NOT the same as
http://mydomain.org/resource/1234

48. Manage local vocabularies and align
them with existing vocabularies
Tools include:
PoolParty
Tematres
Karma

49. Contributing to a collection aggregator –
e.g. Europeana or DPLA
Service
Hub
• Dataset A
• Dataset B
• Dataset C
Service
Hub
• Dataset 1
• Dataset 2
• Dataset 3
Content
Hub
• Dataset X
• Dataset Y
• Dataset Z

50. Publish existing database records as
RDF

51. Managing RDF data in a triple (or quad)
store
• Quad = triple + context
• Most stores feature a SPARQL interface to query across
all triples (quads) in a repository
• Tools:
• Sesame – from OpenRDF
• Virtuoso
• Mulgara

52. Questions?
dhenry@mohistory.org
jmoore@mohistory.org