1 DCS861A-2007 Emerging IT II Rinaldo Di Giorgio Andres Nieto Chris Nwosisi Richard Washington March 17, 2007

2 Definition The WWW developed most rapidly as a medium of documents for people. Semantic Web is an evolving extension of the WWW in which web content can be expressed not only in natural language, but also in a form that can be understood, interpreted and used by software agents, thus permitting them to find, share and integrate information more easily. Software agents will roam the Web sphere carrying sophisticated operations on behalf of their end-users and other automation. It is a vision of the Web as a universal medium for data, information, and knowledge exchange.

3 Main Problem And Drivers Knowledge Representation –Computers must have access to structured information (a language for the data) –Computers must have a set of inference rules (a logic). –Radical departure from traditional AI approaches: paradoxes and unanswerable questions are valid outcomes for an inquiry, global consistency abandoned, single and authoritative sources abandoned. Integration of large and heterogeneous data sets. Large-scale, agent-base mediation.

4 Underlying Technologies URI (anything can link to anything) XML (Metalanguage) RDF (Meaning) RDF/XML, N3, Turtle, N-Triplets (Data exchange) RDF Schema (Structured Vocabularies) Triple Stores (RDF Repositories) SPARQL (Query Language) Ontologies (Knowledge about an application domain) Web Ontology Language (Inference) GRDDL (extracts RDF from XML and XHTML)

5 RDF –Lightweight ontology technology –Triplets: –Single fact, – Well defined meaning –Minimum piece of knowledge that can be represented.

6 RDF Example [2]

7 RDFS [5] Primitives to describe lightweight ontologies in RDF. –Name and declare a vocabulary (name resource types and binary relation types called properties); –Specify the signature of properties (type of the domain i.e. type of the subject and type of the range i.e. type of the object); –Specify the (multiple)-inheritance links between the types of classes (subClassOf); –Specify the (multiple)-inheritance links between the types of properties (subPropertyOf); –To provide labels and comments in natural language to document and display these primitives.

8 RDFS Example [5] Here is an example declaring a class #Man sub class of #Person and #Male, and a property #hasMother sub property of #hasParent, and that is used between instances of the class #Human and instances of the class #Female.

9 Ontologies Careful definition of the terms and concepts of an application domain. Allow for automated interaction even when data is labeled different and uses different format. Tie information on a web page to associated knowledge structure and inference rules. (Objects, properties, values, implicated relations).

10 Ontology Example [3]

11 Tools [4] Editors, Content Management Systems Programming Environments OWL Reasoners RDF Generators On-line Validators SPARQL “Endpoints” Triple Stores, Etc.

12 Criticism AI knowledge representation efforts showed that there is a limit to what you can do with semantic metadata. Natural Language is the proper arena for information. Natural language access to DBs showed that domain modeling is a very hard problem. Natural language processing is going the way of shallow text operations (select, match, show). Information retrieval evolution from cataloguing toward relational simplification (textual matches presented to the user). What logic is best? Classical logics vs. Datalog-related logics. The Ontologies bottlenecks: engineering will always lag behind the domain, are they worth the effort?, correctness, critical mass, intellectual property rights, etc.

13 Other Trends Modeling Languages Self-describing XML (XML + embedded programming) Dynamic Web (Composable services).

14 References [1] Berners-Lee T., Hendler J., Lassila O, The Semantic Web, SCIAM, 2001, [2] Berners-Lee T., Shadbolt N., Hall W., The Semantic Web Revisited, IEEE Intelligent Systems, 2006 [3] Decker,S., et al., The Semantic Web: The Roles of XML and RDF, IEEE Internet Computing, Sep-Oct, 2000 [4] [5] Sematic Web Tutorial, sop.inria.fr/acacia/soft/corese/tutorial.php, 03/11/07http://www- sop.inria.fr/acacia/soft/corese/tutorial.php [6]