Interacting with Linked Data Part I: General Introduction

Transcription

1 Interacting with Linked Data Part I: General Introduction

2 Agenda Part 0: Welcome Part I: General Introduction to Semantic Technologies Part II: Advanced Concepts Part III: OWLIM Part IV: Information Workbench- Part V: Hands-on

3 MOTIVATION SCENARIO 3

4 Music! Provision of a music-based portal. Bring together a number of disparate components of dataoriented content: 1. Musical content (streaming data & downloads) 2. Music and artist metadata 3. Review content 4. Visual content (pictures of artists & albums) 4

5 Data acquisition LD Dataset Access Application Music! Analysis & Mining Module RDFa Visualization Module SPARQL Endpoint Vocabulary Mapping Interlinking Cleansing Integrated Dataset Publishing Physical Wrapper LD Wrapper R2RML Transf. LD Wrapper Streaming providers Musical Content Downloads Metadata RDF/ XML Other content 5

6 Demo Information Workbench: User name: admin Password: iwb Page with sample queries: OWLIM SPARQL Endpoint: User: exercise2 Password: exercise2 6

7 LINKED DATA FOUNDATIONS 7

8 Internet The growth of the Internet Source: 8

9 The Web Billions of diverse documents online, but it is not easily possible to automatically: Retrieve relevant documents. Extract information. Combine information in a meaningful way. Idea: Also publish machine processable data on the web. Formulate questions in terms understandable for a machine. Do this in a standardized way so machines can interoperate. The Web becomes a Web of Data This provides a common framework to share knowledge on the Web across application boundaries. 9

10 The Web: Evolution Web of Documents Web of Data Hyperlinks Typed Links "Documents" "Things" 10

11 Web Technology Basics Uniform Resource Identifier (URI) Compact sequence of characters that identifies an abstract or physical resource. Examples: ldap://[2001:db8::7]/c=gb?objectclass?one news:comp.infosystems. tel: telnet:// :80/ urn:oasis:names:specification:docbook:dtd:xml:

12 Describing Data Vocabularies Collections of defined relationships and classes of resources. Classes group together similar resources. Terms from well-known vocabularies should be reused wherever possible. New terms should be define only if you can not find required terms in existing vocabularies. 12

13 Describing Data Vocabularies A set of well-known vocabularies has evolved in the Semantic Web community. Some of them are: Vocabulary Description Classes and Relationships Friend-of-a-Friend (FOAF) Dublin Core (DC) Semantically-Interlinked Online Communities (SIOC) Music Ontology (MO) Simple Knowledge Organization System (SKOS) Vocabulary for describing people. Defines general metadata attributes. Vocabulary for representing online communities. Provides terms for describing artists, albums and tracks. Vocabulary for representing taxonomies and loosely structured knowledge. foaf:person, foaf:agent, foaf:name, foaf:knows, foaf:member dc:fileformat, dc:mediatype, dc:creator, dc:description sioc:community, sioc:forum, sioc:post, sioc:follows, sioc:topic mo:musicartist, mo:musicgroup, mo:signal, mo:member, mo:record skos:concept, skos:inscheme, skos:definition, skos:example 13

14 Semantics on the Web Semantic Web Stack Berners-Lee (2006) 14

15 Semantics on the Web RDF Resource Description Framework RDF is the basis layer of the Semantic Web stack layer cake. Basic building block: RDF triple. Subject a resource, which may be identified with a URI. Predicate a URI-identified reused specification of the relationship. Object a resource or literal to which the subject is related. 15

16 Semantics on the Web RDF Resource Description Framework (Example) < < < < < "The Beatles". Literals are given in quotes in N-Triples. URIs are given in angle brackets in N-Triples. In N-Triples every statement is terminated with a full stop. 16

17 Semantics on the Web RDF Graphs Every set of RDF assertions can then be drawn and manipulated as a (labelled directed) graph: Resources the subjects and objects are nodes of the graph. Predicates each predicate use becomes a label for an arc, connecting the subject to the object. Subject Predicate Object 17

18 Semantics on the Web RDF Graphs (Example) < < < < "The Beatles" 18

19 Semantics on the Web RDF Turtle Turtle is a syntax for RDF more readable. Since many URIs share same basis we use dbpedia:< And (sometimes) a unique < 21

20 Semantics on the Web RDF Turtle Also has a simple shorthand for class mo:< <artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_> a mo:musicgroup. Is equivalent to: < < < 22

21 Semantics on the Web RDF Turtle When multiple statements apply to same subject they can be abbreviated as follows: <artist/b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#_> rdfs:label "The Beatles"; owl:sameas dbpedia:the_beatles, < Same subject Same subject & predicate b10bbbfc-cf9e-42e0-be17-e2c3e1d2600d#artist>. 23

22 Semantics on the Web RDF Turtle Turtle also provides a simple syntax for datatypes and language tags for literals, respectively: <recording/5098d0a8-d3c3-424e f #_> a mo:signal; rdfs:label "All You Need Is Love" ; mo:duration "PT3M48S"^^xsd:duration. dbpedia:the_beatles dbpedia-owl:abstract "The Beatles were an English rock band formed ( ) "@en, "The Beatles waren eine britische Rockband in den ( ) "@de. 24

23 LINKED DATA 26

24 Linked Data Cloud

25 Linked Data Cloud

26 Linked Data Cloud

27 Linked Data Cloud

28 Linked Data Cloud

29 State of the LOD Cloud 1 Total Datasets: 295 Total Triples: 31,634,213,770 Distribution of triples by domain 1 Version 0.3, 09/19/

30 INTRODUCTION TO SPARQL 33

31 SPARQL * Protocol and RDF Query Language Declarative query language Semantic Web Stack Berners-Lee (2006) 34

32 SPARQL SPARQL Query Declarative query language for RDF data SPARQL Update Declarative manipulation language for RDF data SPARQL Protocol Standard for communication between SPARQL services and clients 35

33 SPARQL Query 1.1 SPARQL 1.0 only allows accessing the data (query) SPARQL 1.1 introduces: Query extensions Aggregates, Subqueries, Negation, Expressions in the SELECT clause, Property paths, assignment, short form for CONSTRUCT, expanded set of functions and operators Updates Data management: Insert, Delete, Delete/Insert Graph management: Create, Load, Clear, Drop, Copy, Move, Add Federation extension Service, values, service variables (informative) CH 5 36

34 SPARQL Basics RDF triple: Basic building block, of the form subject, predicate, object. Example: dbpedia:the_beatles foaf:name "The Beatles". RDF triple pattern: Contains one or more variables. Examples: dbpedia:the_beatles foaf:made?album.?album mo:track?track.?album?p?o. RDF quad pattern: Contains graph name: URI or variable. Examples: GRAPH <:g> {:s :p :o.} GRAPH?g {dbpedia:the_beatles foaf:name?o.} 37

35 QUERYING LINKED DATA WITH SPARQL 38

36 SPARQL Query Main idea: Pattern matching Queries describe sub-graphs of the queried graph Graph patterns are RDF graphs specified in Turtle syntax, which contain variables (prefixed by? ) dbpedia: The_Beatles foaf:made?album Sub-graphs that match the graph patterns yield a result 39

37 SPARQL Query Data: dc:title < musicbrainz.org /record/...> foaf:made dbpedia: The_Beatles foaf:made < musicbrainz.org /record/...> dc:title foaf:made < musicbrainz.org /record/...> dc:title "Help!" "Abbey Road" "Let It Be" Graph pattern: dbpedia: The_Beatles foaf:made?album Results:?album < < < 40

38 SPARQL Query Data: dc:title < musicbrainz.org /record/...> foaf:made dbpedia: The_Beatles foaf:made < musicbrainz.org /record/...> dc:title foaf:made < musicbrainz.org /record/...> dc:title "Help!" "Abbey Road" "Let It Be" Graph pattern:?album Results:?album?title dbpedia: The_Beatles?title dc:title < < < "Help!" "Abbey Road" "Let It Be" 41

39 SPARQL Query Data: foaf:made dbpedia: The_Beatles foaf:made < musicbrainz.org /record/...> mo:track < musicbrainz.org /track/...> dc:title dc:title "Help!" mo:record mo:track "Help!" Graph pattern:?album Results:?album dbpedia: The_Beatles a < mo:record 42

40 SPARQL Query: Components PREFIX dbpedia: < PREFIX foaf: < PREFIX dc: < PREFIX mo: < SELECT?album FROM < WHERE { dbpedia:the_beatles foaf:made?album.?album a mo:record ; dc:title?title } ORDER BY?title Prologue: Prefix definitions Subtly different from Turtle syntax - the final period is not used 43

41 SPARQL Query: Components PREFIX dbpedia: < PREFIX foaf: < PREFIX dc: < PREFIX mo: < SELECT?album FROM < WHERE { dbpedia:the_beatles foaf:made?album.?album a mo:record ; dc:title?title } ORDER BY?title Query form: ASK, SELECT, DESCRIBE or CONSTRUCT SELECT retrieves variables and their bindings as a table 44

42 SPARQL Query: Components PREFIX dbpedia: < PREFIX foaf: < PREFIX dc: < PREFIX mo: < SELECT?album FROM < WHERE { dbpedia:the_beatles foaf:made?album.?album a mo:record ; dc:title?title } ORDER BY?title Data set specification: This clause is optional FROM or FROM NAMED Indicates the sources for the data against which to find matches 45

43 SPARQL Query: Components PREFIX dbpedia: < PREFIX foaf: < PREFIX dc: < PREFIX mo: < SELECT?album FROM < WHERE { dbpedia:the_beatles foaf:made?album.?album a mo:record ; dc:title?title } ORDER BY?title Query pattern: Defines patterns to match against the data Generalises Turtle with variables and keywords N.B. final period optional 46

44 SPARQL Query: Components PREFIX dbpedia: < PREFIX foaf: < PREFIX dc: < PREFIX mo: < SELECT?album FROM < WHERE { dbpedia:the_beatles foaf:made?album.?album a mo:record ; dc:title?title } ORDER BY?title Solution modifier: Modify the result set ORDER BY, LIMIT or OFFSET re-organise rows; GROUP BY combines them 47

45 Query Forms SPARQL supports different query forms: ASK tests whether or not a query pattern has a solution. Returns yes/no SELECT returns variables and their bindings directly CONSTRUCT returns a single RDF graph specified by a graph template DESCRIBE returns a single RDF graph containing RDF data about resource 48

46 Summary You have seen so far RDF Turtle syntax Linked Data Introduction to SPARQL

47 Euclid ebook Course Other euclidproject euclidproject EUCLID - Providing Linked Data 50

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