Building Blocks of Linked Data

Transcription

1 Building Blocks of Linked Data

2 Technological foundations Identifiers: URIs Data Model: RDF Terminology and Semantics: RDFS, OWL

3 23,019,148 People s Republic of China 20,693,000 population located in capital located in population name Shanghai Beijing 上海 located in Graph Triple SJTU name SJTU name "Shanghai Jiao Tong University" SJTU located in Shanghai Shanghai Jiao Tong University Shanghai name " 上海 " Shanghai population "23,019,148" Shanghai located in People s Republic of China People s Republic of China capital Beijing Beijing located in People s Republic of China Beijing population "20,693,000"

4 RDF* Subject Predicate Object SJTU located in Shanghai Shanghai name " 上海 " Shanghai population "23,019,148" Beijing population "20,693,000" Subject Predicate Object *Resource Description Framework

5 RDF N-Triples Syntax Subject Predicate Object <sjtu> <located_in> <shanghai>. <shanghai> <name> "\u4e0a\u6d77". <shanghai> <population> " ". <beijing> <population> " ". Subject Predicate Object

6 RDF Resources and Literals Resource Resource Resource <sjtu> <located_in> <shanghai>. <shanghai> <name> "\u4e0a\u6d77". <shanghai> <population> " ". <beijing> <population> " ". Resource Resource Literal

7 23,019,148 peoples_ republic_of _china 20,693,000 population located in capital located in population name shanghai beijing 上海 located in sjtu name Shanghai Jiao Tong University

8 Resources URIs URI URI URI <sjtu> <located_in> <shanghai>. <shanghai> <name> "\u4e0a\u6d77". <shanghai> <population> " ". <beijing> <population> " ". URI URI

9 Use HTTP-URIs! sjtu, name, located_in: valid URIs, but no scheme, no host, just a path any URI valid: ftp://files.nasa.gov, sjtu, urn:isbn: , etc. but: RDF is datamodel for the Web Web is based on HTTP HTTP-URIs can be resolved, looked up use HTTP-URIs:

10 Use HTTP-URIs! < < < < < "\u4e0a\u6d77". < < " ". < < " ".

11 Qualifying Literals <shanghai> <name> <shanghai> <name> <shanghai> <name> <shanghai> <population> " "^^< <beijing> <population> " "^^< <knud> <birthdate> " "^^< language datatype

12 Named Graphs divide RDF graph in a dataset into several subgraphs each subgraph labelled with a URI useful for keeping track of provenance, timestamps, versioning, etc. not officially part of the standard, but widely supported by tools (and by SPARQL, see tomorrow)

13 RDF Summary Graph data model for the Web Triples (or statements ): <subject> <predicate> <object> (or <thing> <relationship> <thing>) Resources Things about which we want to make statements URIs (ideally HTTP URIs) Literals: Values like strings, numbers, dates, booleans, Either language tag (zh, en, ) or XML Schema datatype Subjects and predicates are always resources Objects can be resources or literals Named Graphs (not standard): divide graph into subgraphs

14 RDF Summary N-Triples Syntax: most basic RDF syntax; very verbose one triple per line line terminated with. resources (URIs) enclosed in < > literals enclosed in " " qualify literals with language or with datatype: ^^<

15 Turtle data: vocab: xsd: < define prefixes group triples with same subject data:shanghai vocab:located_in data:peoples_republic_of_china ; vocab:name "Shang-hai"@ga, "Shanghai"@en, " 上海 "@zh ; vocab:population " "^^xsd:int. abbreviate URIs as CURIEs data:sjtu vocab:located_in data:shanghai ; vocab:name "Shanghai Jiao Tong University"@en. Unicode group triples with same subject,predicate

16 CURIEs Compact URIs replace URI up to last element with prefix namespace define prefix in Turtle: xsd xsd: <

17 Turtle: Group Triples use ; to group triples with same subject data:shanghai vocab:located_in data:peoples_republic_of_china. data:shanghai vocab:name "Shang-hai"@ga. data:shanghai vocab:name "Shanghai"@en. data:shanghai vocab:name " 上海 "@zh. data:shanghai vocab:population " "^^xsd:int. data:shanghai vocab:located_in data:peoples_republic_of_china ; vocab:name "Shang-hai"@ga ; vocab:name "Shanghai"@en ; vocab:name " 上海 "@zh ; vocab:population " "^^xsd:int.

18 Turtle: Group Triples use, to group triples with same subject,predicate data:shanghai vocab:name data:shanghai vocab:name data:shanghai vocab:name " 上海 data:shanghai vocab:name " 上海

19 Turtle - Summary human-readable, less verbose syntax Turtle is based on N-Triples (N-Triples Turtle) Unicode shorten URIs with CURIEs group triples with common elements

20 Other Syntaxes RDF/XML XML-based syntax still widely used, but less readable than Turtle RDFa RDF embedded in HTML, using element attributes JSON-LD JSON serialisation Named Graph Support: Trig (Turtle), Trix (RDF/XML), N-Quads (N-Triples)

21 Vocabularies (Ontologies, Schemata) URIs are globally unique, so we can use globally valid terminology necessary for data integration inferencing Vocabularies define properties to use as predicates classes to assign types to resources just like software libraries, vocabularies are data libraries

22 Vocabularies: Examples FOAF (Friend of a Friend): People, Organisations, Social Networks schema.org (Google, Yahoo!, Bing, Yandex): cross-domain, what search engines are interested in (people, events, products, locations) Dbpedia (Wikipedia as LOD): cross-domain Dublin Core (Bibliographic): publications, authors, media, etc. Good Relations: business, products, etc.

23 Where do Vocabularies Come from?

24 Defining Vocabularies RDF is self-describing (it s triples all the way down ): RDF vocabularies are also defined in RDF special terms to define other terms what is a relationship ( property )? what is a type of thing ( classes )? documentation class and property hierarchies other semantics from rdf, rdfs (RDF Schema) and owl (Web Ontology Language) namespaces

25 FOAF Examples: Some foaf: people: < people:knud a foaf:person ; foaf:name "Knud Möller"@de ; foaf:knows people:victor. people:victor a foaf:person ; foaf:name "Victor de Boer"@nl ; foaf:knows people:knud.

26 FOAF Examples: Classes foaf:person a rdfs:class, owl:class ; rdfs:label "Person" ; rdfs:comment "A person." ; owl:disjointwith foaf:organization, foaf:project ; rdfs:subclassof < < foaf:agent ; rdfs:isdefinedby <

27 FOAF Examples: Properties foaf:name a rdf:property, owl:datatypeproperty ; rdfs:label "name" ; rdfs:comment "A name for some thing." ; rdfs:domain owl:thing ; rdfs:range rdfs:literal ; rdfs:subpropertyof rdfs:label ; rdfs:isdefinedby <

28 Some Terms to Define Terms rdf:type (or just a in Turtle) special property to say what kind of a thing ("class") a resource is rdfs:label, rdfs:comment documentation for humans rdfs:class, owl:class this term is a class rdfs:property, owl:datatypeproperty, owl:objectproperty this term is a property, special kind of property

29 Some Terms to Define Terms rdfs:subclassof defining class hierarchies rdfs:subpropertyof defining property hierarchies rdfs:definedby where is this term defined, where can I get the specification?