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The W3C’s Semantic Web

The W3C’s Semantic Web. Kyle Mosack. The Semantic Web.

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The W3C’s Semantic Web

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  1. The W3C’s Semantic Web Kyle Mosack

  2. The Semantic Web • "The Semantic Web is not a separate Web but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation." It is a source to retrieve information from the web (using the web spiders from RDF files) and access the data through Semantic Web Agents or Semantic Web Services.” Source: "The Semantic Web" by Tim Berners-Lee, James Hendler, and Ora Lassila, Scientific American, 2001

  3. What It Could Be • Machine Readable Data View • Having data on web be defined an linked in a way that can be read by machine for automation, integration, and re-use across different applications • Intelligent Agent View • Agents retrieve and manipulate pertinent information • Distributed Data View • Provide sufficient flexibility to be able to represent all databases and logic rules to link them together • Automated Infrastructure View • Current web lacks an easy automation framework

  4. What it Could Be • Servant of Humanity View • Enable Web applications to automatically collect , integrate, and process information and interoperate with other applications • Better Annotation View • Annotations expressed in a machine processable form and linked together • Improved Searching View • Access Web content by concepts instead of keywords • Web Services View • Expand services from existing web by automating services with Web agents

  5. Semantic Web Layer Cake

  6. Semantic Web Layer Cake

  7. Readable Description Framework • Designed for specific data about specific subjects • Can represent Data and Metadata • Moves proprietary data to a form computers can analyze • Recommendation from W3C for Semantic Web

  8. RDF • To be successful RDF must be able to • Describe most kinds of data that will be available • Describe structural design of data sets • Describe relationships between bits of data

  9. RDF • Creates a data model with triplets • Subject, predicate (property), object (property value) • These are statements about resources • Identified by URI • Easily convertible • Not limited by predefined database values • Flexible

  10. RDF Graph with Anonymous Nodes

  11. RDF Applications • Mozilla • Uses XUL (extensible user interface language) • Uses RDF as a source for listings and other control information that defines which XUL files to use for specific XUL interfaces • RSS (Really Simple Syndication) • Helps spread summaries of personal blogs cheaply and easily • Uses RDF’s XML exchange format • One of the few RDF applications that is distributed over the Web rather than being used locally, unlike Mozilla application • Can be seen as an early, maybe primitive, Semantic Web Application

  12. RDF Applications • RDF for annotations: Annotea • Experimental scheme by W3C for annotating Web pages • Bibliographic meta data: Dublin Core • Provides practical standard terms applicable to nearly any published work • Webscripter: Fusing Information • DAML (DARPA Agent Markup Language) • Ability to make up web pages so that information about the page can be extracted in a uniform way and combined with other web pages

  13. RDF and the Semantic Web • Abilities beyond conventional database • Combine data with different data sets that don’t follow the same data models • Add data that doesn’t fit the table structures • Exchange data with any other application that can handle RDF • Use an RDF processor that can do logical reasoning to discover unstated relationships • Use someone else’s ontology to learn more about own data • Add statements about publications and references that have been defined somewhere else on the Web • Do all these things using well defined standards, so wide range of applications can process the data

  14. RDF – Potential Problems • Many stem from nature of the Web • Incomplete information • Contradictory or unreliable information • Full first order logic requires an ability to generate general statements about the whole table • No way to negate statements • May not be powerful enough

  15. Ontology • Study of existence or being • The kinds of things that can be talked about in a system or context • Provides the means to classify these properties • Name and label them • Kinds of organization include • Lists, hierarchies, and trees

  16. Ontology • The ontology of a complicated semantic system can capture enough knowledge so a computer can perform everyday knowledge • To define a set of classes that together cover a domain of interest • Framework provides syntax, vocabulary, and some pre-defined terms • Framework is an ontology for constructing ontology

  17. Ontology Considerations • Merging Ontology • Terms and classes can by understood by more than one ontology • Can be accomplished by using same system (like OWL) • Even if able to merge, inconsistencies could jeopardize reliability • Imports of second ontology should be kept simple and be done so in small sections

  18. Merging Ontology

  19. Ontology Considerations • Problems with importing a large Ontology • Vocabulary may change over time once ontology is developed • Already committed to the vocabulary that is distributed • Can be limited by designer but no solutions have been made available

  20. Ontology Languages • Frameworks with Web-like uses • RDFS • Resource Description Framework Schema Specification • Base RDF language for describing ontology • Built on top of RDF • RDF makes statements about resources, making assertions about a subject • Every RDFS statement is a legal RDF Statement • RDF classes and properties • Together with standard classes, possible to give basic characteristics of classes for an ontology • Not enough power to express many constraints or logical properties

  21. Ontology Languages • OWL (Web Ontology Language) • Final Recommendation by W3C • Built to standardize a more capable Ontology Framework than RDFS • Need to restrict Cardinality • Express optionally • Combine classes

  22. Ontology Summary • To be useful for the semantic Web, an ontology language must be: • Able to reference concepts defined elsewhere on Web • Sharable over the Web • Be able to work with one or more languages • Able to merge several different ontologies • Widely accepted as a standard • Expressive enough for serious use • Support logical functions that are needed to conduct business of the semantic Web • Last two points are questioned abilities of OWL

  23. Logic • Uses in the Semantic Web • Applying and evaluating rules • Inferring facts that haven’t been explicitly stated • Explaining why a particular conclusion has been reached • Detecting contradictory statements and claims • Specifying ontology and vocabulary of all kinds • Representing knowledge • Describing the kinds of things that may be said about a subject • How those statements are to be understood • The statement and execution of queries to obtain information from stores of data • Combining information from distributed sources in a coherent way

  24. Logic • There is considerable risk that an opensystem will absorb contradictory or incorrect information • Most reasoning systems can not capture explanations • Ones that are able to can not do so in a uniform, easy to read way • More current versions of RDF define ways to understand a collection of RDF statements that can deal with the possibility of contradictory information • Requires more computing power

  25. Logic • Logic and Ontology • Ontology defines concepts and terms • Logic provides ways to make statements that define the use of concepts and terms • To reason about collections of statements that use the concepts and terms

  26. Logic • Logic and Representing Knowledge • Logic is a formal discipline dealing mostly with formal language that can express a subset of everything that can be articulated using natural language • Formal description of data and information naturally involves the use of logic

  27. Logic • Queries • Logical descriptions of information to be retrieved from a database • Queries will need to operate across distributed sources of data to be effective in the Semantic Web • Needs to reconcile the differences in ontology and deal with problems of contradictory data

  28. Logic • Problems of Semantic Web logic looks to deal with • When trying to decide what data should be imported from remote database • Size of the knowledge base might be too large and overwhelm resources • Importing data without duplicating knowledge • How much is interconnected? • Don’t want to import automatically because of a formation of any new data • Importing unreliable information • Contaminate good data

  29. Trust • With development in utility of Web, trust needs to be established between system and user • Trust • Identity: Who are you? • Why should I trust you? • Who else trusts you? • How much should I trust you? • How do I know that you said what you claimed you have said?

  30. Trust • Belief • How much confidence should I place in what you say? • What should I believe when different facts don’t agree • How much should my prior beliefs influence my confidence in what you say? • How can I establish the correct degree of belief for a given set of information?

  31. Tools of Trust • Keys – Private and Public • Digests • Special summary of a document or message that can not be reversed to the original, no key needed • Slight differences in messages amount to large differences in digest • Similarity of digests can not be used to predict similarity in messages

  32. Tools of Trust • Public Key Infrastructure (PKI) • Widespread system • Certificate Authority (CA) issues digital certificate • CA trustworthy source • CA signs certificate for other CAs • Creates chain of certifications, eventually amounting to a size that alleviates issues of trust • Potential problems • If CA private key compromised, entire chain untrustworthy • Large cross-certified chains can become unmanageable • CAs may have different standards • Human error and fraud • Digital Signatures • Authenticated by CA or CA chain

  33. Video The Semantic Web

  34. Work Cited Passin, T. B. Explorer's guide to the semantic web. Manning Publications, 2004. Print. http://www.w3schools.com/web/web_semantic.asp http://www.semanticfocus.com/media/insets/semantic-web-layer cake-2.pnghttp://www.xml.com/2003/02/05/graphics/graph1.gif http://www.codeproject.com/KB/books/GuideSemanticWeb/img002.jpg http://searchsoa.techtarget.com/definition/Semantic-Web http://semanticweb.org/wiki/Semantic_Web

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