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The Need “Most of the Web's content today is designed for humans to read, not for computer programs to manipulate meaningfully.” Berners-Lee, T, Hendler, J & Lassila, O ‘The semantic web’, Scientific American, May cs236607

Semantic Processing We want to be able to pose complex search tasks that use the semantics of pieces of information, e.g., I want to purchase a DVD of “Dore the Explorer” at a price lower than 10$. Is such a CD available at amazon.com? 3cs236607

Current search agents are not suitable for such task 4cs236607

Current Solution Use “intelligent” agents The Semantic-Web Approach Content is machine-understandable by being bound to some formal description of itself (i.e. metadata) 5cs236607

Goals Web of data - provides common data representation framework to facilitate integrating multiple sources to draw new conclusions Increase the utility of information by connecting it to its definitions and to its context More efficient information access and analysis cs

Applications Agents that search the Web and retrieve valuable information to the end user Web services that publish their information Programs that try to integrate data of different web services and to produce new results or draw new conclusions from the integrated data cs

Ontologies & Inference Engines “For the semantic web to function, computers must have access to structured collections of information and sets of inference rules that they can use to conduct automated reasoning.” Berners-Lee, T, Hendler, J & Lassila, O ‘The semantic web’, Scientific American, May 2001 cs

The Four Building Blocks 1. XML 2. RDF 3. Ontologies 4. Agents cs

XML “XML allows users to add arbitrary structure to their documents but says nothing about what the structures mean” cs

RDF –Resource Description Framework Meaning encoded in sets of ‘triples’: entities have properties which have values Entities, properties and values all have distinct URIs cs “imagine that we have access to a variety of databases with information about people, including their addresses. If we want to find people living in a specific zip code, we need to know which fields in each database represent names and which represent zip codes. RDF can specify that "(field 5 in database A) (is a field of type) (zip code)," using URIs rather than phrases for each term. ” Berners-Lee, T, Hendler, J & Lassila, O ‘The semantic web’, Scientific American, May 2001 a

Ontologies Database A and Database B may use different fields to contain ‘zip code’ Ontologies sort this out Ontology = ‘a document or file that formally defines the relations among terms’ Ontologies for the web normally have A taxonomy A set of inference rules cs

Agents “Agent based computing appears to be the appropriate paradigm to work in a complex world with multiple ontologies, fragments and multiple inferencing engines.” Stork, Hans-Georg and Mastroddi, Franco, Semantic Web Technologies - a New Action Line in the European Commission’s IST Programme, 2001 cs

The Power of Agents - Integration “The real power of the Semantic Web will be realized when people create many programs that collect Web content from diverse sources, process the information and exchange the results with other programs. The effectiveness of such software agents will increase exponentially as more machine-readable Web content and automated services (including other agents) become available.” Berners-Lee, T, Hendler, J & Lassila, O ‘The semantic web’, Scientific American, May 2001 cs

‘Ambient Intelligence’ “In the next step, the Semantic Web will break out of the virtual realm and extend into our physical world. URIs can point to anything, including physical entities, which means we can use the RDF language to describe devices such as cell phones and TVs.” Berners-Lee, T, Hendler, J & Lassila, O ‘The semantic web’, Scientific American, May 2001 cs

Resource Description Framework cs

17 What is RDF? A part of the semantic-Web activity RDF is a general-purpose language for representing information on the Web Specifically, objects and relationships Designed to allow computer applications to process data based on its semantics Rather than displaying data to humans (as opposed to RSS) An RDF document is actually a labeled graph that is represented in XML The specific language is called RDF/XML W3C recommendation (Feb. 2004)

RDF Data Consists of Triplets RDF data is a set of statements Each statement is a triplet (Resource, Property, Value) Sometimes we refer to a triplet using the terminology of (Subject, Predicate, Object) cs The author of is Yaron Kanza Resource (Subject): myPage.html Property (Predicate): author Value (Object): Yaron Kanza

19 RDF Data Subject Object predicate The basic element: Triple (labeled edge) Person#845 #1002 address postalCode 6941 Haifa city Herzel street RDF document: edge- labeled graph Statement

20 The XML Syntax of RDF page.html John Smith John’s Home Page DC:Creator DC:Title John Smith John’s Home Page

21 Structured Values page.html John Smith John’s Home Page dc:Title dc:Creator Name ... John Smith John’s Home Page

Containers Groups of things: : unordered list; duplicates allowed : ordered list; duplicates allowed : list of alternatives; one will be selected cs

23 A set of fifteen basic properties for describing generalized Web resources The “obvious” mapping of Dublin Core properties into RDF properties has not yet been approved by the Dublin Core initiative, but is generally a good example Dublin Core

24 “Title”: the name given to the resource “Creator”: the person or organization primarily responsible for the resource “Subject”: what the resource is about “Description”: a description of the content “Publisher”: the person or organization responsible for making the resource available “Contributor”: someone who has provided content to the resource other than the creator “Date”: date of creation or publication Dublin Core

25 “Type”: type of resource, such as home page, technical report, novel, photograph… “Format”: data format of the resource “Identifier”: URL, ISBN number, … “Source”: another resource that this resource is derived from “Language”: the language of the content “Relation”: another resource and its relationship to this one “Coverage”: the portion of time or space described by this resource (atlases, histories, etc.) “Rights”: the intellectual property rights adhering to this resource, or a pointer to them Dublin Core

26 Containers: bags, sequences, alternatives aboutEach, aboutEachPrefix Reification (higher order statements) Namespaces and Vocabularies Advanced RDF

27 Manually from HTML or “user domain XML” With special assisting tools – like Protégé, Reggie, DC- dot, RDF for XML Ideally – with some automated procedure from HTML/XML documents Can we use XSLT there? Creating RDF documents

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RDF Schema RDF Schema (RDFS) enriches the data model of RDF, adding vocabulary and associated semantics for Classes and subclasses Properties and sub-properties Typing of properties Support for describing simple ontologies Adds an object-oriented flavor But with a logic-oriented approach and using “open world” semantics cs

30 Not an XML Schema! A “companion” specification for RDF spec Class, Type, subClassOf, domain, range Misc: label, comment, isDefinedBy,etc. RDF Schema

cs <rdf:RDF xmlns:rdf= " xmlns:rdfs=" xml:base= " <rdf:type rdf:resource=" <rdf:type rdf:resource=" Horse is defined as subclass of animal Example

<rdf:RDF xmlns:rdf= " xmlns:rdfs=" xml:base= " cs Abbreviated version. Works because an RDFS class is an RDF resource. Use rdfs:Class instead of rdfDescription and drop the rdf:type information

RDF and RDF Schema John Smith <rdfs:subclassOf rdf:resource= “ u:Chair John Smith rdf:type g:name g:Person g:name rdfs:Classrdfs:Property rdf:type rdfs:subclassOf rdfs:domain

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RDF Schema is Limited We cannot express facts such as Two classes are disjoint Build a class that is the union of two classes Cardinality restriction Scope of properties Provide relationships between properties, such as transitive, unique, inverse cs

OWL A Web ontology language that is more expressive than RDF and RDF Schema Written in XML on top of RDF Using OWL we want to provide exact descriptions of items and the relationships between them Basically, built upon Description Logics cs

SPARQL Protocol and RDF Query Language cs

SPARQL SPARQL = Query Language + Protocol + XML Results Format Access and query RDF graphs Product of the RDF Data Access Working Group We will only provide some examples and will not go over the entire definition of the language cs

39 SPARQL Query PREFIX dc: SELECT ?title2 WHERE { ?doc dc:title "SPARQL at speed". ?doc dc:creator ?c. ?docOther dc:creator ?c. ?docOther dc:title ?title2 } On an abstracts/papers database: “Find other papers by the authors of a given paper.”

40 SPARQL Query PREFIX dc: PREFIX foaf: PREFIX shop: SELECT ?title WHERE { ?doc dc:title ?title. FILTER regex(?title, "SPARQL"). ?doc dc:creator ?c. ?c foaf:name ?name. OPTIONAL { ?doc shop:price ?price } } “Find books with ‘SPARQL’ in the title. Get the authors’ name and the price (if available).” Multiple vocabularies

41 Inference An RDF graph may be backed by inference −OWL, RDFS, application, rules PREFIX rdf: SELECT ?type WHERE { ?x rdf:type ?type. } :x rdf:type :C. :C rdfs:subClassOf :D | type | ======== | :C | | :D |

42 Another Example PREFIX dc: PREFIX ldap: PREFIX foaf: SELECT ?name ? { ?doc dc:title ?title. FILTER regex(?title, “SPARQL”). ?doc dc:creator ?reseacher. ?researcher ldap: ? . ?researcher ldap:name ?name } “Find the name and addresses of authors of a paper about SPARQL”

Links / / cs

SPARQL Links Jena: Java and.Net Semantic Web Framework SPARQL Query SPARQL Protocol SquirrelRDF: Access legacy SQL: cs