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Semantic Web

Semantic Web. Quratulain Rajput Faculty of Computer Science, IBA Spring2013. Semantic Web Technologies. How thing can be identified How knowledge can be expressed

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Semantic Web

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  1. Semantic Web Quratulain Rajput Faculty of Computer Science, IBA Spring2013

  2. Semantic Web Technologies • How thing can be identified • How knowledge can be expressed • How models that lay behind or above this represented facts can also be explicitly represented with in the web using languages of semantic web. Quratulain Rajput

  3. Semantic Web Technologies Quratulain Rajput

  4. A Layered Approach Quratulain

  5. A Layered Approach • The development of Semantic Web proceeds in steps, each step building a layer on top of another. • The purpose of layered approach is that it is easier to achieve consensus on small steps. Quratulain

  6. A Layered Approach • In building a Semantic Web layer two principal should be followed: • Downward compatibility • Upward partial understanding Quratulain

  7. Semantic Web Layers • URL: • E.g www.iba.edu.pk • URI: • E.ghttp://dbpedia.org/resource/pakistan • XML layer • Syntactic basis • RDF layer • RDF basic data model for facts • RDF Schema simple ontology language • Ontology layer • More expressive languages than RDF Schema • Current Web standard: OWL

  8. Semantic Web Layers • Logic layer(writing of rules) • enhance ontology languages further • application-specific declarative knowledge • Proof layer (execution of rules) • Proof generation, exchange, validation • Trust layer (evaluates whether to trust the proof or not) • Digital signatures • recommendations, rating agencies ….

  9. RDF • RDF(Resource Description Framework), document describes as directed graph. • In contrast, XML is encoded in tree structure. • Tree structure processed efficiently then why need graphs. Reasons are: • RDF is not for structuring the documents, but rather for describing general relationships between object of interest (semantic knowledge). which is natural represent in the form of graphs. • RDF is description language for data on web , where web store manage data in decentralized way. Easy to combine graph structure form multiple sources. Quratulain Rajput

  10. URI • To distinguish resources from each other. • Every URL is a valid URI • URI also used as identifiers in RDF document that has clear identity in the context of the given application: books, places, people, event etc. • URI that are not URL are some time called URN(Uniform Resource Names), exclusively for unique identification (directory path) Quratulain Rajput

  11. From Graph to Triple • In graph, situation become complicated for storage and management as the size of graph increases. • Therefore, represent graph as character strings. • RDF represent using following syntax: • Turtle • XML (most commonly used syntax b/c many programming languages support it) Quratulain Rajput

  12. RDF • XML is a TREE structure while RDF is Graph. • XML does not provide any semantics about data. • For example: no meaning associated with the nesting of tags. • RDF data model is an abstract, conceptual layer independent of XML • consequently, XML is a transfer syntax for RDF, not a component of RDF • RDF data might never occur in XML form Quratulain

  13. Introduction No standard way of assigning meaning to tags nesting • Suppose to express the fact: Ahmed is a lecturer of Discrete Mathematics • Possibilities are: <course name=“Discrete Mathematics”> <lecturer> Ahmed </lecturer> </course> <lecturer name=“Ahmed”> <teaches>Discrete Mathematics</teaches> </lecturer> <teachingOffering> <lecturer>Ahmed</lecturer> <course>Discrete Mathematics </course> </teachingOffering> Quratulain

  14. RDF • RDF is a data model. • Its basic building block is an object-attribute-value triple, called statement. • Syntax in XML (standard by W3C) • Domain independent, It is up to user to define their own terminology in schema called RDFS Quratulain

  15. RDF value resource property • Fundamental concept of RDF are • Resource • Properties • Statements Quratulain

  16. Resource • Resource is an object (we want to talk about) • Ex. Book, places, people, hotel and so on. • Every resource has URI. • URI can be a URL or some kind of unique identifier Quratulain

  17. Properties • Describe relationship between resource. • Ex. writtenBy, age, title, etc • Properties in RDF are also identified by URI Quratulain

  18. Statement • A statement is an object-attribute-value triple, consisting of a resource, property and a value. • Value can be either resource or literal. Quratulain

  19. Example • The owner of web page (http://www.iba.edu.pk/faculty) is Wasim http://www.iba.edu.pk/faculty owner Wasim <rdf:Descriptionrdf:about=“http://ww.iba.edu.pk/faculty”> <owner> Wasim </owner> </rdf:Description> Quratulain

  20. Logical formula http://www.iba.edu.pk/faculty owner Wasim As logical formula P(x,y), where P is binary predicate relates object Wasim to object http://www.iba.edu.pk/faculty. Quratulain

  21. Example • Sana knows Asif. • Sana’s surname is Malik. • Asif knows Faisal. • Salman works with Faisal. How would you represent this? Draw graph. Quratulain

  22. Example Subject Object Predicate knows knows Sana Asif Faisal worksWith surName Literal Salman “Malik” Quratulain

  23. Reading Assignment • http://www.huffingtonpost.com/steve-hamby/semantic-web-technology_b_1228883.html Quratulain Rajput

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