RDFa From Theory to Practice

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RDFa From Theory to Practice - Part 1 - A gentle introduction to Linked Data and the Semantic Web?

12th July 2010

Institutional Web Management Workshop 2010University of Sheffield, UK

Adrian Stevenson



semantics is … devoted to the study of meaning … on the syntactic levels of words, phrases, sentences

http://en.wikipedia.org/wiki/Semantic



“The Semantic Web is a web of data, in some ways like a global database”1

“first step is putting data on the Web in a form that machines can naturally understand... This creates what I call a Semantic Web - a web of data that can be processed directly or indirectly by machines”2

1. http://www.w3.org/DesignIssues/Semantic.html

2. Tim Berners-Lee, Weaving the Web. Harper, San Francisco. 1999.



“The term Linked Data refers to a set of best practices for publishing and connecting structured data on the Web.”

“the Semantic Web is the goal or end result… Linked Data provides the means to reach that goal”

From ‘Linked Data: The Story So Far’ - Heath, Bizer and Berners-Lee 2009



The Web We’re Used To

• Made by humans for humans

• Primarily documents

• Machines not very welcome

• Data silos



Web of Linked Data

• In 1998 the idea from Tim Berners-Lee of ‘linked data’ took shape

• Designed for machines first

• It primarily links data about ‘things’, not documents

• …but it is for humans in the end



• But haven’t we been putting data on the web for years?– In CSV , relational databases, XML etc?

• Well yes, but these approaches are not so easy to integrate

• Web 2.0 mashups work against a fixed set of data sources

• Linked Data applications operate on top of an unbound, global data space.



So what’s happening now?



• “Sir Tim Berners-Lee, the inventor of the world wide web, will help the British government to make its data more easily available online … I have asked Sir Tim Berners-Lee … to help us drive the opening up of access to Government data in the web” Prime Minister Gordon Brown, 10th June 2009

• "What you find if you deal with people in government departments is that they hug their database, hold it really close”. Tim Berners-Lee, 10th June 2009

• An Institute of Web Science proposed• Why?

– Openness – MPs expenses, etc.– Saving money

http://www.guardian.co.uk/technology/2010/may/25/berners-lee-institute-web-science-statement

http://www.ecs.soton.ac.uk/about/news/3223

Data.gov.uk

Officially launched 21st January 2010

Data.gov.uk – search for ‘traffic’

Central Office of Information - http://coi.gov.uk/

BBC Music BETA

http://www.bbc.co.uk/music/developers

• Provides access to raw data (Excel spreadsheets, PDF files, and more)

• UK is adhering more closely to Berners- Lee’s Linked Data rules

http://www.readwriteweb.com/archives/cnet_partners_with_thomson_reuters_on_linked_data.php

http://open.blogs.nytimes.com/2009/06/26/nyt-to-release-thesaurus-and-enter-linked-data-cloud/

Graphs house prices over time - combines house price data with information from Yahoo! Placemaker, Nestoria and OpenStreetMap

Postcode Paper - bus timetables, doctors surgeries, allotmentshttp://blog.newspaperclub.co.uk/2009/10/16/data-gov-uk-newspaper/

Owls Near You - http://owlsnearyou.com/

12 month project funded by JISC 2/10 jiscExpo callhttp://blogs.ukoln.ac.uk/locah/ http://www.twitter.com/projectlocah tag: #locah

http://richard.cyganiak.de/2007/10/lod/



A little bit of the techy stuff



Linked Data is …

• A way of publishing data on the web that:– Encourages reuse– Reduces redundancy– Maximises inter-connectedness– Enables network effects

• So how is this achieved?



Presentational tagging – HTML

• <h1>Agilitas Physiotherapy Centre</h1> <p>Welcome to the Agilitas Physiotherapy Centre home page. Do you feel pain? Have you had an injury? Let our staff Lisa Davenport, our secretary Kelly Townsend, and Steve Matthews take care of your body and soul.</p>

<h2>Consultation hours</h2> Mon 11am - 7pm<br/> Tue 11am - 7pm<br/> Wed 3pm - 7pm<br/> Thu 11am - 7pm<br/> Fri 11am - 3pm

• <p> But note that we do not offer consultation during the weeks of the <a href=". . .">State Of Origin</a> games.</p>



Semantic tagging<company>

<treatmentOffered>Physiotherapy</treatmentOffered>

<companyName>Agilitas Physiotherapy Centre</companyName>

<staff>

<therapist>Lisa Davenport</therapist><therapist>Steve Matthews</therapist>

<secretary>Kelly Townsend</secretary>

</staff>

</company>



Tim BL’s Linked Data Design Issues• Use URIs as names for things • Use HTTP URIs so that people can look up those

names. • When someone looks up a URI, provide useful

information, using the standards (RDF, SPARQL) • Include links to other URIs so that they can

discover more things.

• From http://www.w3.org/DesignIssues/LinkedData.html



URIs and HTTP

• A “Uniform Resource Identifier (URI) provides a simple and extensible means for identifying a resource –RFC 3986

• A URL is a type of URI• HTTP URIs can be ‘de-referenced’

• HTTP URIs are used for “real world” things– http://adrianstevenson.com/id/me– http://dbpedia.org/page/Tim_Berners-Lee



RDF• Resource Description Framework

– “a language for representing information about resources in the World Wide Web”

– “RDF can also be used to represent information about things that can be identified on the Web, even when they cannot be directly retrieved on the Web”

• Describes relations based on triples– Subject-object-predicate

• http://www.w3.org/TR/REC-rdf-syntax/



Heroes

has a

creator whose name is

David Bowie

Subject

Predicate

Object



RDFa• ‘Resource Description Framework in

attributes’

• Adds attribute level extensions to XHTML

• Enables embedding RDF triples within XHTML

• Google and Yahoo process RDFa



RDFa example<html xmlns:dc="http://purl.org/dc/terms/">

<head>

<title>RDFa: From Theory to Practice</title>

</head>

<body>

<h1>RDFa: From Theory to Practice</h1>

Author: <em property="dc:creator" content=”Adrian Stevenson">Adrian Stevenson</em>

Created: <em property="dc:created" content="2010-07-12"> July 12th, 2010</em>

License: <a rel="license" href="http://creativecommons.org/licenses/ » by-sa/3.0/">CC Attribution-ShareAlike</a>

</body>

</html>



RDFa example<html xmlns:dc="http://purl.org/dc/terms/">

<head>

<title>RDFa: From Theory to Practice</title>

</head>

<body>

<h1>RDFa: From Theory to Practice</h1>

Author: <em property="dc:creator" content=”Adrian Stevenson">Adrian Stevenson</em>

Created: <em property="dc:created" content="2010-07-12"> July 12th, 2010</em>

License: <a rel="license" href="http://creativecommons.org/licenses/ » by-sa/3.0/">CC Attribution-ShareAlike</a>

</body>

</html>



Linked Data in Use



Publishing Linked Data• RDFizers – convert data formats into

RDF

• D2R Server – creates linked data from relational databases

• SparqPlug – Extracts linked data from HTML

• …. Many others

D2R server publishes Linked Data view of database and allows clients to query the database via SPARQL



Linked Data Applications

• Linked Data Browsers – navigate between data sources– Disco– Tabulator– Marbles

• Linked Data Search Engines– For humans – Falcons, SWSE– For apps – Swoogle, Sindice

• Tracks provenance of data• Merges data about the same thing from different sources

http://marbles.sourceforge.net/

• User can explore the underlying data structures

• Can search for objects, concepts or documents

http://iws.seu.edu.cn/services/falcons/

• Provides interface (API) that other linked data apps can use• Rationale: new linked data apps shouldn’t need to implement their own infrastructure for crawling and indexing web of data

http://sindice.com/

http://sindice.com/search?q=jazz&qt=term



Some issues

• To RDF or not to RDF• Usability• Sustainability• Provenance• Licensing• Reliability



Sustainability

• Ed Summers at the Library of Congress createdhttp://lcsh.info

• Linked Data interface for LOC subject headings

• People started using it

Library of Congress Subject Headings

Data Licensing

• Uses Amazon Web Services but contravenes their terms and conditions

http://www4.wiwiss.fu-berlin.de/bizer/bookmashup/



Provenance

• OK if data ‘watermarked’

• But can often be a problem

• VOID can help





• Can we convince IT Managers, VC etc. it’s worth it?– Realistic expectations– “..the people sort of in charge of the kind

of data thing knew so little about their data structures”

– “I’ve had a whole bunch of meetings to get one dataset, been fobbed off, and literally just never get anywhere”Tom Steinberg, Director of MySociety (from Nodalities issue 8)

The Business Case



• What’s the payoff for O’Reilly, BBC etc of using Linked Data?

• Why didn’t it work the first time?– What’s different now?• Need to work out what Linked Data does

that other things don’t• prove a simple tangible benefit

The Business Case



Universities and Colleges in the Giant Global Graph

• Session at CETIS Conference 2009

• Case for Linked Data / Semantic Web discussed

• Some cases:– Freedom of Information– Improves data quality– Joining the party

http://wiki.cetis.ac.uk/Universities_and_Colleges_in_the_Giant_Global_Graph

http://wiki.cetis.ac.uk/Image:Conf2009_GGG_Group1B.jpg



Conclusion• Interesting developments and sense of

momentum• Central Gov’t still seem committed• JISC is funding 10 Linked Data projects

starting around July 2010• … but still much to do if the semantic web

and linked data are to really take hold



Questions?

• http://blogs.ukoln.ac.uk/adrianstevenson• http://www.twitter.com/adrianstevenson• [email protected]



CC Attribution

• Some sections of this presentation adapted from:– An Introduction to Linked Data, by Tom Heath– The Semantic Web – An Introduction by Owen Stephens– Using Linked Data as a Learning Resource

Recommendation System by Chris Clarke

• This presentation available under creative commons Noncommercial-Share Alike

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