Lecture the semantic_web_part_1
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    Lecture the semantic_web_part_1 Lecture the semantic_web_part_1 Presentation Transcript

    • The Semantic Web – Part 1Semantic CMS Community Lecturer Organization The Vision and Basic Date of presentation Technologies of the Semantic Web. Co-funded by the 1 Copyright IKS Consortium European Union
    • Page: Part I: Foundations(1) Introduction of Content Foundations of Semantic (2) Management Web Technologies Part II: Semantic Content Part III: Methodologies Management Knowledge Interaction Requirements Engineering(3) (7) and Presentation for Semantic CMS(4) Knowledge Representation and Reasoning (8) Designing Semantic CMS Semantifying(5) Semantic Lifting (9) your CMS Storing and Accessing Designing Interactive(6) Semantic Data (10) Ubiquitous ISwww.iks-project.eu Copyright IKS Consortium
    • Page: 3 What is this Lecture about? Semantic web technologies as a possible solution for improving the „state of play“ in content management by making semantics expressable in machine-readable way The Semantic Web  The vision behind the semantic web  Underlying technologies of the Semantic Web Part I: Foundations (1) Introduction of Content Foundations of Semantic (2) Management Web Technologies www.iks-project.eu Copyright IKS Consortium
    • Page:Web evolution Slide by Nova Spivack, Radar Networkswww.iks-project.eu Copyright IKS Consortium 4
    • Page: 5 The Semantic Web Thevision of the Semantic Web has been originally proposed by Tim Berners-Lee “TheSemantic 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.” [The Semantic Web, 2001] Standardized specification techniques for the semantic annotation of content (RDF, OWL, ...) www.iks-project.eu Copyright IKS Consortium
    • Page: 6 Semantic Web Stack W3C provides standardized specifications for Semantic Web technologies Semantic Web Layer Cake as a conceptual architecture describes an hierarchy of languages Each layer exploits and uses capabilities of the layers below Semantic Web Layer Cake, Image source: http://www.w3.org/2007/03/layerCake.svg www.iks-project.eu Copyright IKS Consortium
    • Page: 7 Unique Identification of Resources “...more fundamental than either HTTP or HTML are URIs, which are simple text strings that refer to Internet resources -- documents, resources, people, and indirectly to anything. URIs are the glue that binds the Web together. IRIs extend and strengthen the glue, by allowing people to identify Web resources in their own language.” In a “Web of Data” the unique identification of entities is required www.iks-project.eu Copyright IKS Consortium
    • Page: 8 How to identify resources? URI – Uniform Resource Identifier [RFC 3986]  “A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource.”  A URI consists of five parts: scheme, authority, path, query and fragment  URI = scheme ":" authority "/" path [ "?" query ] [ "#" fragment ] Example: http://user@example.com:8042/over/there?name=ferret#nose scheme authority path query fragment www.iks-project.eu Copyright IKS Consortium
    • Page: 9 How to identify resources? IRI – Internationalized Resource Identifier [RFC 3987]  “IRIs are defined similarly to URIs in [RFC3986], but the class of unreserved characters is extended by adding the characters of the UCS (Universal Character Set, [ISO10646]) ..”  Extends the character set used by URIs and thereby allows the consideration of language specific syntaxes (e.g. Japanese, Chinese, ...) Example  Logical Hebrew http://ab. .ij/kl/mn/op.html  ASCII notation http://ab.CDEFGH.ij/kl/mn/op.html www.iks-project.eu Copyright IKS Consortium
    • Page: 10 Structuring Data XML – Extensible Markup Language  XML can be used to specify the syntactical structure of documents or complex data objects in a machine-readable form <car> <brand>Jaguar</brand> <model>XF</model> <dimensions> <length>4961</length> <width>2070</width> </dimensions> <engine>5.0 L V8 Petrol</engine> </car> www.iks-project.eu Copyright IKS Consortium
    • Page: 11 Why isn´t XML enough? XML tags are only defining the structure of a document For a machine the tags have no semantics! <car> <cat> <brand>Jaguar</brand> <brand>Jaguar</brand> ... ... </car> </cat> The difference in meaning is only recognized by a human. www.iks-project.eu Copyright IKS Consortium
    • Page: 12 Why isn´t XML enough? The relation among the different tags is not expressed explicitly <car> The relation between “car”, “brand” and “Jaguar” is only recognizable <brand>Jaguar</brand> by a human. ... </car> www.iks-project.eu Copyright IKS Consortium
    • Page: 13 What do we need? We want to express the statement:  “The brand of the car is Jaguar.” We need ...  ...a way to address the concrete resource car.  ... to express the property brand of the resource car.  ... to define the property value Jaguar for the property brand. www.iks-project.eu Copyright IKS Consortium
    • Page: 14 Resource Description Framework (RDF) “TheResource Description Framework (RDF) identifies things using Web identifiers (URIs), and describes resources with properties and property values.” A Resource is an object that can be identified by an URI, e.g. “http://example.org/Car”. A Property describes an aspect of a resource, e.g. “http://example.org/Brand”. The property is also identified by an URI. TheProperty value assigns a concrete value to a property, e.g. “Jaguar” or ““http://example.org/Jaguar”. www.iks-project.eu http://www.w3schools.com/rdf/ Copyright IKS Consortium
    • Page: 15 RDF Statements RDF statements consist of subject (resource), predicate (property) and object (property value) Predicate Object Subject (URI) Predicate Object (literal) Subjects (except Blank Nodes) and Predicates are always defined by URIs Objects can be defined by URIs and literals www.iks-project.eu Copyright IKS Consortium
    • Page: 16 RDF Statements - Example Exemplary statements:  “The brand of the car is Jaguar.”  “The model of the car is XF.”Subject Predicate Object http://example.org/rel/Brand http://example.org/Car http://example.org/Jaguar http://example.org/rel/Model XF PredicateObject www.iks-project.eu Copyright IKS Consortium
    • Page: 17 Resource Description Framework (RDF) “The Resource Description Framework (RDF) is a language for representing information about resources...” [RDF Primer]• W3C Standard (http://www.w3.org/RDF) RDF provides a graph-based data model  for representing metadata  for describing the semantics of information in a machine-accessible way www.iks-project.eu Copyright IKS Consortium
    • Page: 18 RDF Serialization Formats RDF/XML N3 N-Triples TRiG TRiX Turtle JSON JSON-LD RDFa www.iks-project.eu Copyright IKS Consortium
    • Page: 19 RDF/XML RDF/XML is the most common serialization format for RDF statements Example: <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rel="http://example.org/rel/"> <rdf:Description rdf:about="http://example.org/Car"> <rel:Brand rdf:resource="http://example.org/Jaguar"/> </rdf:Description> <rdf:Description rdf:about="http://example.org/Car"> <rel:Model>XF</rel:Model> </rdf:Description> </rdf:RDF> http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 20 Root Element and Namespaces Root element of the RDF/XML document.<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rel="http://example.org/rel/">....</rdf:RDF> Defined namespaces<rdf:RDF> Root element of RDF documentsxmlns:rdf Specifies that elements with the “rdf” prefix are using the namespace “..”xmlns:abc Specifies that elements with the “abc” prefix are using the namespace “..” www.iks-project.eu Copyright IKS Consortium
    • Page: 21 Description Element Node element<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rel="http://example.org/rel/"> <rdf:Description rdf:about="http://example.org/Car"> ... </rdf:Description> ... Assigns a resource to the node element.</rdf:RDF><rdf:Description> Introduces node element (subject).<rdf:about> Defines the URI reference for the node element. www.iks-project.eu Copyright IKS Consortium
    • Page: 22 Objects defined by Resources  Assigning resources to objects (property values) in RDF/XML <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"Defines predicate “Brand” xmlns:rel="http://example.org/rel/"> in namespace “rel”. <rdf:Description rdf:about="http://example.org/Car"> <rel:Brand rdf:resource="http://example.org/Jaguar"/> </rdf:Description> </rdf:RDF> object The is defined by a resource. http://example.org/rel/Brand http://example.org/Car http://example.org/Jaguar www.iks-project.eu Copyright IKS Consortium
    • Page: 23 Objects defined by Literals Definition of objects (properties) with constant values (literals)<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rel="http://example.org/rel/"> <rdf:Description rdf:about="http://example.org/Car"> <rel:Model>XF</rel:Model> </rdf:Description></rdf:RDF> The object is defined http://example.org/Car by a literal. http://example.org/rel/Model XF www.iks-project.eu Copyright IKS Consortium
    • Page: 24 RDF Container Elements “A container is a resource that contains things. The contained things are called members. The members of a container may be resources (including blank nodes) or literals.” Container provide the ability to describe groups of things, e.g. several authors of a book RDF defines three types of containers:  Bag  Sequence  Alternatives http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 25 Container Element - Bag “ABag (a resource having type rdf:Bag) represents a group of resources or literals, possibly including duplicate members, where there is no significance in the order of the members.” Example:  Describe equipment features of the car. http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 26 Container Element - Bag http://www.w3.org/1999/0 2/22-rdf-syntax-ns#Bag http://example.org/Car http://www.w3.org/1999/02/22-rdf-syntax-ns#typehttp://example.org/features#equipment http://example.org/AC http://www.w3.org/1999/02/22-rdf-syntax-ns#_1 http://www.w3.org/1999/02/22-rdf-syntax-ns#_2 http://example.org/CarRad io Blank Node http://www.w3.org/1999/02/22-rdf-syntax-ns#_3 http://example.org/SeatHe ating www.iks-project.eu Copyright IKS Consortium
    • Page: 27 Container Element - Bag The subject “Car” is <rdf:RDF described by the xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" predicate “equipment”. xmlns:e="http://example.org/features#"> <rdf:Description rdf:about="http://example.org/Car"> <e:equipment> <rdf:Bag> The different members <rdf:li rdf:resource="http://example.org/AC"/> <rdf:li rdf:resource="http://example.org/CarRadio"/> of the Bag container <rdf:li rdf:resource="http://example.org/SeatHeating"/> are listed. The object is </rdf:Bag> acontainer of type “Bag” </e:equipment> </rdf:Description> </rdf:RDF> <x:xyz> Defines predicate “xyz” in namespace “x”. <rdf:Bag> Defines a container of type “Bag”. <rdf:li> Defines members of the Bag container. www.iks-project.eu Copyright IKS Consortium
    • Page: 28 Container Element - Sequence “ASequence or Seq (a resource having type rdf:Seq) represents a group of resources or literals, possibly including duplicate members, where the order of the members is significant.” Example:  Describe a list of previous owners of the car in chronological order. http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 29 Container Element - Sequence http://www.w3.org/1999/0 http://example.org/Car 2/22-rdf-syntax-ns#Seq http://www.w3.org/1999/02/22-rdf-syntax-ns#typehttp://example.org/owner#preOwners http://example.org/JohnD oe http://www.w3.org/1999/02/22-rdf-syntax-ns#_1 http://www.w3.org/1999/02/22-rdf-syntax-ns#_2 http://example.org/RickMi ller http://www.w3.org/1999/02/22-rdf-syntax-ns#_3 http://example.org/Sarah House www.iks-project.eu Copyright IKS Consortium
    • Page: 30 Container Element - Sequence The subject “Car” is <rdf:RDF described by the xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" predicate “preOwners”. xmlns:p="http://example.org/owner#"> <rdf:Description rdf:about="http://example.org/Car"> <p:preOwners> <rdf:Seq> The different members <rdf:li rdf:resource="http://example.org/JohnDoe"/> <rdf:li rdf:resource="http://example.org/RickMiller"/> of the Sequence <rdf:li rdf:resource="http://example.org/SarahHouse"/> container are listed. The object is a</rdf:Seq> </p:preOwners>container of type </rdf:Description> “Sequence”. </rdf:RDF><x:xyz> Defines predicate “xyz” in namespace “x”.<rdf:Seq> Defines a container of type “Sequence”.<rdf:li> Defines members of Sequence container. www.iks-project.eu Copyright IKS Consortium
    • Page: 31 Container Element - Alternative “An Alternative or Alt (a resource having type rdf:Alt) represents a group of resources or literals that are alternatives (typically for a single value of a property).” Example:  Describe a list of possible colors of the car. http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 32 Container Element - Alternative http://www.w3.org/1999/0 2/22-rdf-syntax-ns#Alt http://example.org/Car http://www.w3.org/1999/02/22-rdf-syntax-ns#typehttp://example.org/exterior#colors http://example.org/Black http://www.w3.org/1999/02/22-rdf-syntax-ns#_1 http://www.w3.org/1999/02/22-rdf-syntax-ns#_2 http://example.org/White http://www.w3.org/1999/02/22-rdf-syntax-ns#_3 http://example.org/Green www.iks-project.eu Copyright IKS Consortium
    • Page: 33 Container Element - Alternative The subject “Car” is <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" described by the xmlns:c="http://example.org/exterior#" predicate “colors”. <rdf:Description rdf:about="http://example.org/Car"> <c:colors> <rdf:Alt> The different members <rdf:li rdf:resource="http://example.org/Black"/> <rdf:li rdf:resource="http://example.org/White"/> of the Alternative <rdf:li rdf:resource="http://example.org/Green"/> container are listed. The object is a</rdf:Alt> </c:colors>container of type </rdf:Description> “Alternative”. </rdf:RDF><x:xyz> Defines predicate “xyz” in namespace “x”.<rdf:Alt> Defines a container of type “Alternative”.<rdf:li> Defines members of Alternative container. www.iks-project.eu Copyright IKS Consortium
    • Page: 34 RDF Collections A RDF Container can be used to define groups, but lacks the ability to “close” them. That means to define that "these are all the members of the container". RDF Collections provide the ability to describe groups, that contain only the specified resources. “An RDF collection is a group of things represented as a list structure in the RDF graph.” Example:  All equipment features of a car. http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ www.iks-project.eu Copyright IKS Consortium
    • Page: 35 RDF Collection http://example.org/Carhttp://example.org/features#equipment http://www.w3.org/1999/02/22-rdf-syntax-ns#_first http://example.org/AChttp://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/02/22-rdf-syntax-ns#_first http://example.org/CarRa diohttp://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/02/22-rdf-syntax-ns#_first http://example.org/SeatH eatinghttp://www.w3.org/1999/02/22-rdf-syntax-ns#rest http://www.w3.org/1999/0 2/22-rdf-syntax-ns#nil www.iks-project.eu Copyright IKS Consortium
    • Page: 36 RDF Collection The predicate<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" “equipment” is described xmlns:e="http://example.org/features#"> by a Collection. <rdf:Description rdf:about="http://example.org/Car"> <e:equipment rdf:parseType="Collection"> <rdf:Description rdf:about="http://example.org/AC"/> <rdf:Description rdf:about="http://example.org/CarRadio"/> <rdf:Description rdf:about="http://example.org/SeatHeating"/> </e:equipment> </rdf:Description></rdf:RDF><x:xyz Defines that the predicate “xyz” isrdf:parseType=“Collection”> described by a collection. www.iks-project.eu Copyright IKS Consortium
    • Page: 37Validation Tool www.iks-project.eu http://www.w3.org/RDF/Validator/ Copyright IKS Consortium
    • Page: 38 Semantic Layer Web Cake A model for describingresources with properties A format for specifying structured and property values. data in a machine-readable form Unique identification of resources Semantic Web Layer Cake, Image source: http://www.w3.org/2007/03/layerCake.svg www.iks-project.eu Copyright IKS Consortium
    • Page: 39 RDF RDF provides a model for describing resources with properties and property values. @prefix ex: <http://www.example.org/>. ex:Car1 ex:Brand ex:Jaguar ex:Car1 ex:Colour “Black” ex:Car2 ex:Brand ex:Jaguar ex:Car2 ex:Colour “White” ex:Car3 ex:Brand ex:VW ex:Car3 ex:Colour “Black” www.iks-project.eu Copyright IKS Consortium
    • Page: 40 SPARQL SPARQL Protocol and RDF Query Language W3C Recommendation since 2008 SPARQL provides a standard for querying information, that is specified in RDF SPARQL consists of three specifications  Query language  Query results XML format  Data access protocol www.iks-project.eu Copyright IKS Consortium
    • Page: 41 Exemplary SPARQL Query“Return the models and prices for all cars of brand„Jaguar‟ ” Declares namespaces for abbreviated resourcesSPARQL Query: identifiers. PREFIX ex: <http://example.org/> Identifies the variables to SELECT ?model ?price WHERE appear in the query { ?car ex:Brand ex:Jaguar . results. ?car ex:Model ?model . ?car ex:Price ?price . } Provides the basic graph pattern to match againstExemplary Result: the data graph. Model Price “XJ” “79.750,00” “XF” “44.900,00” www.iks-project.eu Copyright IKS Consortium
    • Page: 42 Basic Graph Patterns (BGP) A SPARQL query contains a set of triple patterns called a basic graph pattern Triple patterns are like RDF triples except that each of the subject, predicate and object may be a variable. A basic graph pattern matches a subgraph of the RDF data when RDF terms from that subgraph may be substituted for the variables and the result is a RDF graph equivalent to the subgraph. WHERE Variables are { ?car ex:Brand ex:Jaguar . defined by ?car ex:Model ?model . “?varname” or ?car ex:Price ?price . } “$varname” www.iks-project.eu Copyright IKS Consortium
    • Page: 43 Group Graph Patterns “Fora Group Graph Pattern, a set of graph patterns must all match” Ina SPARQL query string, a group graph pattern is delimited with braces: {...} PREFIX ex: <http://example.org/> SELECT ?model ?price WHERE { { ?car ex:Brand ex:Jaguar . ?car ex:Model ?model . } ?car ex:Price ?price . } www.iks-project.eu Copyright IKS Consortium
    • Page: 44 Optional Pattern Matching Basic graph patterns allow applications to make queries where the entire query pattern must match. It is useful to be able to have queries that allow information to be added to the solution where the information is available, but do not reject the solution because some part of the query pattern does not match. If the optional part does not match, it creates no bindings but does not eliminate the solution. www.iks-project.eu Copyright IKS Consortium http://www.w3.org/TR/rdf-sparql-query
    • Page: 45 Optional Pattern Matching Example: PREFIX ex: <http://example.org/> SELECT ?model ?price WHERE { ?car ex:Brand ex:Jaguar . ?car ex:Model ?model . OPTIONAL { ?car ex:Price ?price . } } Result Model Price “XJ” “79.750,00” “XF” “44.900,00” “S-Type” www.iks-project.eu Copyright IKS Consortium
    • Page: 46 Scope of Filters “A constraint, expressed by the keyword FILTER, is a restriction on solutions over the whole group in which the filter appears.” PREFIX ex: <http://example.org/> SELECT ?model ?price WHERE { ?car ex:Brand ex:Jaguar . ?car ex:Model ?model . ?car ex:Price ?price . FILTER (?price < 50.000,00) } Result: Model Price “XF” “44.900,00” www.iks-project.eu Copyright IKS Consortium
    • Page: 47 Unary Operators (1/2) Operator Type(A) Result Type BOUND(A) variable xsd:boolean IsURI(A) RDF term xsd:booleanisBLANK(A) RDF term xsd:booleanisLITERAL(A) RDF term xsd:boolean www.iks-project.eu Copyright IKS Consortium
    • Page: 48 Unary Operators (2/2) Operator Type(A) Result Type STR(A) literal simple literal STR(A) URI / IRI simple literal LANG(A) literal simple literalDATATYPE(A) typed literal URI / IRIDATATYPE(A) simple literal URI / IRI www.iks-project.eu Copyright IKS Consortium
    • Page: 49 Binary Operators (1/2)Operator Type(A) Type(B) Result Type A= B A != B numeric numeric A<B simple literal simple literal xsd:string xsd:string xsd:boolean A> B xsd:boolean xsd:boolean xsd:dateTime xsd:dateTime A <= B A >= B www.iks-project.eu Copyright IKS Consortium
    • Page: 50 Binary Operators (2/2) Operator Type(A) Type(B) Result Type sameTERM RDF term RDF term xsd:boolean (A,B) langMATCHES simple literal simple literal xsd:boolean (A,B) REGEX simple literal simple literal xsd:boolean (A,B) Filter can be combined by “&&” or “||” www.iks-project.eu Copyright IKS Consortium
    • Page: 51 Alternative Graph Patterns “SPARQL provides a means of combining graph patterns so that one of several alternative graph patterns may match. If more than one of the alternatives matches, all the possible pattern solutions are found.” Pattern alternatives are syntactically specified with the UNION keyword. PREFIX ex: <http://example.org/> SELECT ?office WHERE { ?x rdf:type ex:CarManufacturer . { ?x ex:Headquarter ?office . } UNION { ?x ex:Office ?office . } } www.iks-project.eu Copyright IKS Consortium
    • Page: 52 Solution Sequences and Modifiers “Query patterns generate an unordered collection of solutions. These solutions are then treated as a sequence (a solution sequence), initially in no specific order; any sequence modifiers are then applied to create another sequence.” There are several use cases in which the results shall be presented in a defined order, e.g. alphabetical order Shall duplicates be presented or deleted? www.iks-project.eu Copyright IKS Consortium
    • Page: 53 Order By “Followingthe ORDER BY clause is a sequence of order comparators, composed of an expression and an optional order modifier (either ASC() or DESC()). Each ordering comparator is either ascending (indicated by the ASC() modifier or by no modifier) or descending (indicated by the DESC() modifier).” PREFIX ex: <http://example.org/> SELECT ?constructionYear ?price WHERE { ?car ex:Brand ex:Jaguar . ?car ex:ConstructionYear ?constructionYear . ?car ex:Price ?price . } ORDER BY DESC(?constructionYear) ?price . www.iks-project.eu Copyright IKS Consortium
    • Page: 54 Some more Solution Sequence Modifiers LIMIT  “The LIMIT clause puts an upper bound on the number of solutions returned. If the number of actual solutions is greater than the limit, then at most the limit number of solutions will be returned.” OFFSET  “OFFSET causes the solutions generated to start after the specified number of solutions. An OFFSET of zero has no effect.” SELECT DISTINCT  “The DISTINCT solution modifier eliminates duplicate solutions. Duplicates are eliminated before either limit or offset is applied.” www.iks-project.eu Copyright IKS Consortium
    • Page: 55 Semantic Web Layer CakeA language for queryinginformation specified in RDF. A model for describingresources with properties A format for specifying structured and property values. data in a machine-readable form Unique identification of resources Semantic Web Layer Cake, Image source: http://www.w3.org/2007/03/layerCake.svg www.iks-project.eu Copyright IKS Consortium
    • Page: 56 Lessons Learned Now you should know ...  ... the general idea of the Semantic Web and the differences to the World Wide Web.  ... the underlying technologies of the Semantic Web.  ... how resources can be identified and specified.  .. the importance of XML for expressing data in a machine- readable way.  ... the concept of the RDF and the way it is expressed (e.g.: RDF/XML).  ... how SPARQL can used to query data specified in RDF. www.iks-project.eu Copyright IKS Consortium
    • Page: 57 References and Additional Material Introduction to RDF  http://www.w3schools.com/rdf/rdf_intro.asp RDF Syntax Specification  http://www.w3.org/TR/2004/REC-rdf-syntax-grammar- 20040210 RDF Validation Tool  http://www.w3.org/RDF/Validator/ www.iks-project.eu Copyright IKS Consortium