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Semantic Web

Explore the principles and architecture of the Semantic Web, knowledge representation technologies like XML and RDF, and the role of ontologies in making the web understandable by computers.

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Semantic Web

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  1. Semantic Web Based on: -The semantic web -Ontologies Come of Age Clément Troprès - Damien Coppéré

  2. Plan • Introduction to semantic web • Kwnoledge Representation • Ontologies • Agents Clément Troprès - Damien Coppéré

  3. 1. Introduction to semantic web • Today, most of the web contents is designed for human to read • The actual web looks insufficient • The semantic web purpose is to structure the world wide web Clément Troprès - Damien Coppéré

  4. 1. Introduction to semantic web • Principles: • Each object of the web has a metadata • Each metadata is readable by agents and humans • Each metadata represents accurately an object • Each metadata is available in a common space, readable by agents and humans. The selection of the metadata makes the object avalaible as a resource Clément Troprès - Damien Coppéré

  5. 1. Introduction to semantic web The semantic web architecture Clément Troprès - Damien Coppéré

  6. 2. Knowledge representation (1): • Technology which permits computers to access to structured collections of information • System must have sets of inference rules that computers can use to conduct automated reasoning • It has to be linked into a single global system Clément Troprès - Damien Coppéré

  7. 2. Knowledge representation (2) : • Traditional systems usually : - Limit the questions that can be asked - Become unmanageable • New systems, in contrast, accept paradoxes - Unanswerable questions are a price that must be paid to achieve versatility. Clément Troprès - Damien Coppéré

  8. 2. Knowledge representation (3) : • Two important technologies exist : - EXtensible Markup Language (XML) - Resource Description Framework (RDF) • XML : - Everyone can create their own tags - It allows to add arbitrary structure to the document Clément Troprès - Damien Coppéré

  9. 2. Knowledge representation (4) : • RDF : - Encode in sets of triplets - Each triple being rather like the subject, predicate and object of an elementary sentence identified by URIs - Natural way to describe the vast majority of the data processed by machines - Example : New York has a postal abbreviation which is NY <rdf:Description rdf:about="urn:states:New%20York"> <"http://purl.org/dc/terms/" :alternative>NY</rdf:Description> • Universal Resource Identifier - Ensure that concepts are tied to a unique definition that everyone can find on the Web Clément Troprès - Damien Coppéré

  10. 3. Ontologies - Introduction • Current web : It has grown and continues to grow very quickly Problems to find information you are really looking for Designed for human perception • Semantic web: Make the web understandable by computers agent Clément Troprès - Damien Coppéré

  11. 3. Ontologies - Introduction • How make the web semantic? - Complete HTML tag (with XML) - Organize the keywords in each document - Indexing all the resources of the web (RDF) - Ontologies Clément Troprès - Damien Coppéré

  12. 3. Ontologies - Introduction We are here Clément Troprès - Damien Coppéré

  13. 3. Ontologies - Introduction • Definition: - In 1993, Gruber propose his definition (which is now the most cited in AI) : « An ontology is an explicit specification of a conceptualization ». (Gruber T., 1993b) - In 1997, Borst modified slightly the definition in order to highlight major aspects of this paradigm: « An ontology is a formal specification of a shared conceptualization ». (Borst W. N., 1997) Clément Troprès - Damien Coppéré

  14. 3. Ontologies - Introduction • Definition: In 1998, these two definitions were only one in the definition of Studer. « An ontology is a formal, explicit specification of a shared conceptualization ». (Studer R. et al., 1998) - « Conceptualization » refers to an abstraction of a phenomenon obtained by identifying the concepts appropriate to this phenomenon - « Shared » means that ontology captures consensual knowledge Clément Troprès - Damien Coppéré

  15. 3. Ontologies - Introduction • « Formal » means that ontology is interpretable by a machine (machinereadable) • « explicit specification » means that the concepts of ontology and the constraints related to their use are defined in a declaratory way • Ontology has the following characteristics : 1) shared, 2) explicit, 3) formal Clément Troprès - Damien Coppéré

  16. 3.Ontologies – Possible representation? • A controlled vocabulary (eg: Catalogs) • A glossary (list of terms) • Thesauri (synonym relationship…, but not an explicit hierarchy) • Term hierarchies (without true subclass) • Strict subclass hierarchies • Frames (classes include property information) • Value restriction (eg: a price is a number) • Logical deduction A A is a superclass of B B Clément Troprès - Damien Coppéré

  17. 3. Ontologies – Simple Ontologies • Some of the ways that simple ontologies may be used in practice: • A controlled vocabulary (beginning of interoperability) • Site organization and navigation support • Expectation setting • Umbrella structures from which to extend content • Browsing support • Search support • Sense disambiguation support Clément Troprès - Damien Coppéré

  18. 3. Ontologies – Structural Ontologies • Consistency checking • Completion • Interoperability support • Support validation and verification testing • Encode entire test suites • Configuration support • Support structured, comparative and customized search • Exploit generalization/specialization information Clément Troprès - Damien Coppéré

  19. 3. Ontologies – Implications and Needs • An ontology-based application has two major concerns: The language The environment Clément Troprès - Damien Coppéré

  20. 3. Ontologies – Implications and Needs (1) • The language: Simple ontologie: It’s not a real problem (language with subclass and instance relationships) Structural ontologie: the language must be able to express the entire domain unambiguously (KRSS, KIF, OKBC) Clément Troprès - Damien Coppéré

  21. 3. Ontologies – Implications and Needs (2) • Environment: Ontology tools are needed to analyze, modify and maintain an ontology over time Many are avalaible commercially Clément Troprès - Damien Coppéré

  22. 3. Ontologies – Implications and Needs (3) • Environment – Criterias needed : - Collaboration and distributed workforce support (share session) - Platform interconnectivity (able to read and write compatible formats) - Scale (In terms of size of ontologies, number of simultaneous users) - Versioning (Able to support many versions of ontology) Clément Troprès - Damien Coppéré

  23. 3. Ontologies – Implications and Needs (4) • Environment – Major criteria of performance : - Security - Analysis (focus the user’s attention in areas which need modification) - Lifecyle issues (Support for ontology evolution issues) - Ease of use (training materials, tutorials…) - Diverse user support - Presentation style - Extensibility (Adapt along with the needs) Clément Troprès - Damien Coppéré

  24. 4. Agents • Representing by programs : - Collect Web content from diverse sources - Process the information - Exchange the results with other programs • All agents can work together Clément Troprès - Damien Coppéré

  25. 4. Agents (2) • Important facets : - "Proofs" written in the Semantic Web's unifying language (Proof Markup Language PML) - Digital signatures used to verify that the attached information has been provided by a specific trusted source • Example of agent : You answer your phone and the stereo sound which was working is turned down. Clément Troprès - Damien Coppéré

  26. 4. Agents (3) • You want to buy a car … An intelligent Agent is going to find your new car - How ? It looks for all cars which corespond to your criterias - Which criteria ? Prices, delivery period, colour… - Where ? On web documents described by semantic standards (proofs, digital signature…) • Travel Agency… Clément Troprès - Damien Coppéré

  27. The Semantic Web - Lets anyone express new concepts with minimal effort - Unifies a logical language Clément Troprès - Damien Coppéré

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