Transcript Publishing to the Semantic Web
Publishing to the Semantic Web
Dr Owen Conlan Dr Alexander O’Connor
The Long Road for Semantic Web
The World
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Wide Web HTTP HTML The Semantic
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Web Vision RDF Semantic Web Stack Web 2.0 / The
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Social Web Tagging Crowd Sourcing The Web of
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Data (Linked Data) VoID DBpedia
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Semantic Web Reasoning Logic, Rules Trust 1992 1998/9 2003 2006 ????
The Linked Data Movement
• • • • Tim Berners Lee driven “Linked Data uses a small slice of the technologies that make up the Semantic Web” Treat Schemas as Vocabularies Reuse existing schemas
Linking Open Data Project
• • • Community project with W3C support started in early 2007 Idea: take existing (open) data sets and make them available on the Web in RDF Interlink them with other data sets
A Pretty (Scary) Diagram
DBpedia
• • • Transforming Wikipedia into a knowledge base • • • • Structure from Infoboxes HTML (titles) Categories Links other languages, redirects, disambiguations, etc Uses: as a controlled vocab, as an ontology Check out : http://dbpedia.org/page/Trinity_Coll ege,_Dublin (or Google “Trinity College Dublin dbpedia”)
Linking Data
• Publish structured data in RDF on the web using URIs and shared vocabularies rather than the traditional Semantic Web focus on ontologies and inference • • • Lowers barriers to entry Fosters widespread adoption Mature tools, techniques, patterns
Linked Data Principles
• Formulated by Tim Berners-Lee (2006): 1.
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Use URIs as names for things Use HTTP URIs so that people/apps can lookup these names When someone/an app looks up a URI, provide useful information Include links to other URIs so that they can discover more things • This not an unambiguous specification, just a set of principles.
http://what.is.http.org/ask?question
• The Hypertext Transfer Protocol (HTTP) is an application-level protocol for distributed, collaborative, hypermedia information systems. It is a generic, stateless, protocol which can be used for many tasks beyond its use for hypertext, such as name servers and distributed object management systems, through extension of its request methods, error codes and headers. A feature of HTTP is the typing and negotiation of data representation, allowing systems to be built independently of the data being transferred. [RFC2616]
URIs
• • • A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource [RFC3986] Syntax: URI = scheme “:” hier-part [“?” query] [“#” fragment] Example Note: scheme not the same as protocol
Identifying Linked Data Resources
• • • Linked data needs dereferenceable URIs (ones we can use HTTP to retrieve a description of that resource) But we cannot serialise people, things over the internet (yet?) => we publish RDF documents on the web that describe them • A real-word object != a document about that object e.g. creation-date for you != creation-date for your web page
Identifying Linked Data Resources
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URI that identifies a real-word object != URI that identifies a document about that object
Can make statements about object and can make statements about the document describing it How do we link these 2 URIs together?
URI styles for Linked Data
• • • • • 303 Redirect (e.g. http://example.uk/people/dave smith) Used for large, dynamic data sets Flexible because redirection can be separately configured for each resource e.g. can store data in multiple files or DB. Can change this at deployment/run-time.
Typically used for resource descriptions in large data-sets
URI styles for Linked Data
• • • • • • • Fragment (e.g. http://example.uk/people#dave smith) Used for small, static data sets Reduced number of HTTP round-trips => reduced latency A single HTTP request retrieves the entire document May transmit unnecessary data across the web Used for RDFa (defined via RDFa “about=” attribute) Typically used for vocabulary definitions
303 Redirect Approach
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• • • Create URIs for concept/thing and documents e.g. http://biglynx.co.uk/people/dave-smith (URI identifying the person Dave Smith) http://biglynx.co.uk/people/dave-smith.rdf (URI for RDF/XML document describingDave Smith) http://biglynx.co.uk/people/dave-smith.html(URI for HTML document describing Dave Smith) 1.
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Use HTTP redirects/content negotiation to access the desired resource description for the specific user agent Client HTTP GET request on a URI identifying a object Server recognizes URI, it answers using the HTTP 303 to send the URI of a description of the object Client HTTP GET request on new URI Server sends document from new URI
Huh?
• The picture below shows how dereferencing a HTTP URI identifying a non-information resource plays together with content negotiation: • Simples…
Fragment Approach
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• Assign a URI to the RDF document defining the concepts e.g. http://biglynx.co.uk/vocab/sme/ (document URI) 2.
• • Assign fragment identifiers to concepts within the document e.g. http://biglynx.co.uk/vocab/sme#SmallMediumEnterprise http://biglynx.co.uk/vocab/sme#Team 3.
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Use HTTP requests to get the description Client truncates a fragment URI to just refer to the document Send HTTP GET to request the document 3.
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Server sends back the full document Linked data application now inspects triples to find fragment
Now we can refer to stuff
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5 Steps to Publishing Linked Data
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Understand the Principles Understand your Data Choose URIs for Things in your Data Set up Your Infrastructure Link to other Data Sets
Step 1: Understanding the Principles
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• • • Use URIs as names for things Anything, not just documents You are not your homepage Information resources (can be transmitted electronically) and non information resources (cannot be transmitted electronically, e.g. a person!) B.
• • Use HTTP URIs Globally unique names, distributed ownership Allows people to lookup those names
Step 1: Understanding the Principles (cont.)
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• Provide useful information in RDF when someone looks up a URI We can include RDF triple statements!
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• • • • Include RDF links to other URIs To enable discovery of related information e.g. via “follow your nose” browsing Relationship Links – to add context Identity Links – for URI aliases in other sources Vocabulary Links – to enable self-description
Step 2: Understand your Data
• • • • • • • • What are the key things in your data?
People Places Events Book Flims Musician … • This why domain expertise are critically important
Step 2: Understand your Data (cont.)
• What vocabularies can be used to describe these?
• • • Principles: Reuse, don’t reinvent Mix liberally • • • • • Examples: foaf -- Friend-of-a-Friend ontology geonames -- GeoNames ontology skos -- Simple Knowledge Organization System ckan.net
Step 2: Common Vocabularies
• • • • • • • • • • • • bibo -- Bibilographic ontology cc -- Creative Commons ontology damltime -- Time Zone ontology doap -- Description of a Project ontology event -- Event ontolog foaf -- Friend-of-a-Friend ontology frbr -- Functional Requirements for Bibliographic Records geo -- Geo wgs84 ontology geonames -- GeoNames ontology mo -- Music Ontology opencyc -- OpenCyc knowledge base owl -- Web Ontology Language • • • • • • • • • pim_contact -- PIM (personal information management) Contacts ontology po -- Programmes Ontology (BBC) rss -- Really Simple Syndicate (1.0) ontology sioc -- Socially Interlinked Online Communities ontolog sioc_types -- SIOC extension skos -- Simple Knowledge Organization System umbel -- Upper Mapping and Binding Exchange Layer ontology wordnet -- WordNet lexical ontology yandex_foaf -- FOAF (Friend-of-a Friend) Yandex extension ontology
Step 3: Choosing URIs
• • • • • Use HTTP URIs Keep out of other people’s namespaces Create own URI and include alias information • Abstract away from implementation details: http://dbpedia.org/resource/Berlin • Is better than this: http://www4.wiwisss.fu-berlin.de:2020/demos/dbpedia/cgi bin/resource.php?id=/Berlin • • • Use Natural Keys within URIs: Need to ensure the uniqueness of URIs Useful to base them on some existing primary key Whenever possible, use a key that is meaningful within the domain of the data set. e.g. use the ISBN as part of the URI of a book
Step 3: Choosing URIs (cont.)
• • • • Common patterns for URIs: http://dbpedia.org/resource/Berlin Thing http://dbpedia.org/data/Berlin RDF http://dbpedia.org/page/Berlin HTML • • • • Or use the file name extension: http://biglynx.co.uk/people/dave-smith http://biglynx.co.uk/people/dave-smith.html
http://biglynx.co.uk/people/dave-smith.rdf
Step 4: Set up Your Infrastructure
• • • • • Describe the Data-set!
e.g. dataset name, authorship, updates, licensing terms, crawler support, SPARQL endpoint location, ...
• Vocabulary of Interlinked Datasets (VoID) A little later… • • • Pick a Publication Pattern Is your input data: queryable, structured or text?
What is the data volume?
Is it static or dynamic?
Test it
Step 4: Set up Your Infrastructure (cont.)
Step 5: Linking
• • • • • • • • • • Popular predicates for linking owl:sameAs Foaf:depection Foaf:homepage Foaf:topic Foaf:based_near Foaf:maker/foaf:made Foaf:page Foaf:primaryTopic Rdfs:seeAlso
Step 5: Linking (cont.)
• • VoID (from "Vocabulary of Interlinked Datasets") is an RDF based schema to describe linked datasets A dataset is a collection of data, published and maintained by a single provider, available as RDF, and accessible, for example, through dereferenceable HTTP URIs or a SPARQL endpoint http://semanticweb.org/wiki/VoiD
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Understand the Principles Understand your Data Choose URIs for Things in your Data Set up Your Infrastructure Link to other Data Sets
Thank you!
References
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http://linkeddata.org
Debugging Semantic Web sites with cURL, http://dowhatimean.net/2007/02/debugging-semantic-web- sites-with curl Linked Data Tutorial, http://www.slideshare.net/mediasemanticweb/linked-data- michael hausenblas-2009-03-05 Linked Data Applications, M Hausenblas, DERI Technical Report 2009 Linked Data: Evolving the Web into a Global Data Space, Tom Heath , Christian Bizer http://linkeddatabook.com