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Publishing to the Semantic Web Dr Owen Conlan Dr Alexander O’Connor.

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Presentation on theme: "Publishing to the Semantic Web Dr Owen Conlan Dr Alexander O’Connor."— Presentation transcript:

1 Publishing to the Semantic Web Dr Owen Conlan Dr Alexander O’Connor

2 The World Wide Web HTTP HTML The Semantic Web Vision RDF Semantic Web Stack Web 2.0 / The Social Web Tagging Crowd Sourcing The Web of Data (Linked Data) VoID DBpedia Semantic Web Reasoning Logic, Rules Trust The Long Road for Semantic Web / ????

3 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 The Linked Data Movement

4 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 Linking Open Data Project

5 A Pretty (Scary) Diagram

6 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 : ege,_Dublin ege,_Dublin (or Google “Trinity College Dublin dbpedia”)

7 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 Linking Data

8 Formulated by Tim Berners-Lee (2006): 1.Use URIs as names for things 2.Use HTTP URIs so that people/apps can lookup these names 3.When someone/an app looks up a URI, provide useful information 4.Include links to other URIs so that they can discover more things This not an unambiguous specification, just a set of principles. Linked Data Principles

9 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]

10 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 URIs

11 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

12 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? Identifying Linked Data Resources

13 303 Redirect (e.g. 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

14 Fragment (e.g. 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 URI styles for Linked Data

15 1.Create URIs for concept/thing and documents e.g. (URI identifying the person Dave Smith) (URI for RDF/XML document describingDave Smith) for HTML document describing Dave Smith) 2.Use HTTP redirects/content negotiation to access the desired resource description for the specific user agent 1.Client HTTP GET request on a URI identifying a object 2.Server recognizes URI, it answers using the HTTP 303 to send the URI of a description of the object 3.Client HTTP GET request on new URI 4.Server sends document from new URI 303 Redirect Approach

16 The picture below shows how dereferencing a HTTP URI identifying a non-information resource plays together with content negotiation: Simples… Huh?

17 1.Assign a URI to the RDF document defining the concepts e.g. (document URI) 2.Assign fragment identifiers to concepts within the document e.g. 3.Use HTTP requests to get the description 1.Client truncates a fragment URI to just refer to the document 2.Send HTTP GET to request the document 3.Server sends back the full document 4.Linked data application now inspects triples to find fragment Fragment Approach

18 Class

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