Semantic Web
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The document provides an overview of semantic web technologies including: - The history and core principles of the semantic web including RDF, ontologies, and vocabularies. - Methods for publishing and consuming semantic data such as Linked Data, RDFa, microdata, and SPARQL querying. - Some challenges with semantic web technologies including differences between object-oriented programming and description logics, and open world assumptions versus closed world assumptions from relational databases. - Ways that semantic web technologies can help with interoperability, information retrieval, recommendations, and search engine optimization.
![Vocabularies
✤ Schemes:
✤ Taxonomy: narrower/broader
✤ Thesaurus: related
✤ Folksonomy: “machines are (using) us” Peter Mika [Yahoo]
✤ Ontology: “An ontology is a specification of a conceptualization” Tom
Gruber, 1993 [*Siri]](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-13-320.jpg)
![Path queries
✤ ?a :d “D”.
✤ ?a :a ?b. ?b :e “E”; :f “F”.
✤ ?a :b [ :c “C” ].](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-31-320.jpg)
![Path queries
:c
C
:b
✤ ?a :d “D”.
:a :e
?a ?b E
✤ ?a :a ?b. ?b :e “E”; :f “F”.
:d :f
✤ ?a :b [ :c “C” ].
D F](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-32-320.jpg)
![Python RDFLib
from rdflib.graph import Graph, URIRef
from rdflib.namespace import Namespace
from rdflib import plugin
plugin.register('sparql', rdflib.query.Processor,
'rdfextras.sparql.processor', 'Processor')
plugin.register('sparql', rdflib.query.Result,
'rdfextras.sparql.query', 'SPARQLQueryResult')
plugin.register('turtle', rdflib.serializer.Serializer,
'rdflib.plugins.serializers.turtle', 'TurtleSerializer')
namespaces = { 'skos' : Namespace('http://www.w3.org/2004/02/skos/core#'), }
def list_friends(f_name, uri):
g = Graph()
g.parse(f_name, format="n3")
query = "SELECT ?fn WHERE { ?f foaf:knows <%s>; foaf:name ?fn. }" % uri
return [ f for f in g.query(query, initNs=namespaces) ]](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-35-320.jpg)
![OOP vs Description Logic
✤ B rdfs:subClassOf A
C rdfs:domain A
D rdfs:domain B
✤ Infers:
✤ C rdfs:domain B [WRONG!]
✤ D rdfs:domain A [OK]](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-39-320.jpg)
![OOP vs Description Logic
✤ B rdfs:subClassOf A
C rdfs:domain A
D rdfs:domain B domain
A C
✤ Infers: subClassOf
domain
B D
✤ C rdfs:domain B [WRONG!]
✤ D rdfs:domain A [OK]](https://image.slidesharecdn.com/webtuesday-121212072220-phpapp01/85/Semantic-Web-40-320.jpg)
Semantic Web
- 1. Semantic Web Dr. Sebastian Ryszard Kruk Dec 11th, 2012; Web Tuesday, Zurich
- 2. Outline ✤ Quick walk through the history of the Web ✤ The core principles of the Semantic Web ✤ Some vocabularies, schemas and ontologies you should know ✤ Publishing the Web 3.0 way ✤ Consuming semantics ✤ Semantic Web gotchas ✤ Summary: how Semantic Web technologies can help
- 3. The history of the Web
- 4. Let’s go back in time ✤ 1937 - H.G. Wells: “World Brain” ✤ 1945 - Vannevar Bush: Memex ✤ 1969 - Doug Engelbart: ARPANET, online collaboration, mouse ✤ 1989 - sir Tim Berners-Lee: WWW ✤ 1995 - Dublin Core: semantics from librarian world ✤ 1999 - prof. Stefan Decker: OntoBroker ✤ 2000 - DARPA publish DAML specification ✤ 2001 - TBL, Handler i Lassila: “The Semantic Web” (SciAm) ✤ 2009 - TBL - 20th anniversary: “we’ve got all the tools" ✤ 2009 - Google introduces Rich Snippets/RDFa; BestBuy sales increase ✤ 2010 - Facebook starts Open Graph ✤ 2012 - Google announces Knowledge Graph
- 5. The blueprints of the Web
- 8. RDF is not a format!
- 9. RDF is not a format! Leather made by Wood Chair is a made made of is a Carpenter Man sits on is a has Back Leg count used for 4 Sitting
- 10. RDF is not a format! Leather made by Wood Chair is a made predicate subject made of object is a Carpenter a statement Man sits on is a has Back Leg count used for 4 Sitting
- 11. Resource, Literals and BNodes ✤ Resource - everything identified by URI/IRI ✤ Literal - a value (“four”) ✤ with an optional type (4^^xsd:int) ✤ or optional lang tag (“four”@en) ✤ BNode - point in the graph with only local _:name ✤ Statement - a triple (subject, predicate, object) ✤ Reification - a statement about the statement
- 12. Resource, Literals and BNodes ✤ Resource - everything identified by URI/IRI ✤ Literalns: a value (“four”) - <http://test.test/ns> . @prefix @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix xsd: <http://www.w3.org/2001/XMLSchema> . ✤ with an optional type (4^^xsd:int) ns:Chair ns:has ns:Leg. _:sentence a rdf:Statement; tag (“four”@en) or optional lang ✤ rdf:subject ns:Chair; rdf:predicate ns:has; ✤ BNoderdf:object ns:Leg;the graph with only - point in local _:name ns:count “4”^^xsd:int. ✤ Statement - a triple (subject, predicate, object) ✤ Reification - a statement about the statement
- 13. Vocabularies ✤ Schemes: ✤ Taxonomy: narrower/broader ✤ Thesaurus: related ✤ Folksonomy: “machines are (using) us” Peter Mika [Yahoo] ✤ Ontology: “An ontology is a specification of a conceptualization” Tom Gruber, 1993 [*Siri]
- 14. Ontology languages ✤ RDF Schema: classes, properties, domains and ranges ✤ OWL (Web Ontology Language) - Lite, DL and Full, and OWL 2: (among others) inverse functional property, symmetry, transitiveness and disjointness ✤ But also: UML, ERD, ...
- 16. Dublin Core ✤ One of the oldest, originates from digital libraries ✤ Goals: ✤ semantic and syntactic interoperability ✤ shareable descriptions, vocabularies and constrains ✤ Defines: ✤ 15 basic concepts, such as dc:title, dc:creator ✤ Additional classes and concepts in DC Qualifiers
- 17. FOAF+SIOC+SKOS http://sioc-project.org
- 18. Good Relations ✤ De-facto standard for semantic e-commerce ✤ Supported by Google via Rich Snippets ✤ BestBuy showed how to increase revenue with it ✤ Part of the schema.org specification ✤ Example information: ✤ the geo-location of the store ✤ the countries the store ships to ✤ the payment options the ship accepts ✤ Distribute, open “Amazon”
- 19. schema.org ✤ Vocabulary for Rich Snippets and Knowledge Graph ✤ Yahoo+Bing+Google ✤ Microdata vs RDFa (Lite)
- 21. Linked (Open) Data http://linkeddata.org
- 22. 5-Star Data Rules ✤ URIs = names for things ✤ HTTP URIs = enable look up ✤ Provide useful information upon lookup, using the standards (RDF*, SPARQL) ✤ Link to other URIs = enable discovery of more things. http://www.w3.org/DesignIssues/LinkedData.html
- 23. 5-Star Data Rules ✤ URIs = names for things ✤ HTTP URIs = enable look up ✤ Provide useful information upon lookup, using the standards (RDF*, SPARQL) ✤ Link to other URIs = enable discovery of more things. http://www.w3.org/DesignIssues/LinkedData.html
- 25. RDFa and RDFa Lite ✤ Extension to XHTML/HTML5 for embeding RDF graph semantics in HTML syntax: ✤ property vs rel ✤ resource vs about ✤ typeof ✤ vocab, prefix
- 26. RDFa and RDFa Lite ✤ Extension to XHTML/HTML5 for embeding RDF graph semantics in HTML syntax: <p vocab="http://schema.org/" property vs rel ✤ prefix="ov: http://open.vocab.org/terms/" resource="#skruk" typeof="Person"> My name is <span property="name">Sebastian Kruk</span> ✤ resource vs about and you can give me a ring via <span property="telephone">+41-78-87-961-89</span>. <img property="image" src="http://bit.ly/QAYF10" /> My favorite animal is the <span property="ov:preferredAnimal">Hamster</span>. ✤ </p>typeof ✤ vocab, prefix
- 27. Rich Snippets (microdata) <div class="col-right small" itemid="http://example/" itemtype="http://schema.org/ FurnitureStore"> <ul class="list"><li><div itemprop="address" itemscope="" itemtype="http://schema.org/ PostalAddress"> <p> <span itemprop="postalCode">5210</span> <span itemprop="addressLocality">Windisch</ span><br> <span itemprop="addressCountry">Switzerland</span><br> </p> <p> <a class="email" href="mailto:windisch@kruk.me" itemprop="email">windisch@kruk.me</a> <span itemprop="telephone">+41788796189</span><br> </p> </div></li></ul>
- 28. Rich Snippets (RDFa Lite) <div class="col-right small" resource="http://example.com/" typeof="FurnitureStore" vocab="http://schema.org/"> <ul class="list"><li><div property="address" typeof="PostalAddress"> <p> <span property="postalCode">5210</span> <span property="addressLocality">Windisch</ span><br> <span property="addressCountry">Switzerland</span><br> </p> <p> <a class="email" href="mailto:windisch@kruk.me" property="email">windisch@kruk.me</a> <span property="telephone">+41788796189</span><br> </p> </div></li></ul> </div>
- 30. SPARQL ✤ W3C standard for querying RDF graphs ✤ Purposely made similar to SQL (to the extent possible) ✤ SPARQL endpoint: a standard way to expose (open) data published by the service
- 31. Path queries ✤ ?a :d “D”. ✤ ?a :a ?b. ?b :e “E”; :f “F”. ✤ ?a :b [ :c “C” ].
- 32. Path queries :c C :b ✤ ?a :d “D”. :a :e ?a ?b E ✤ ?a :a ?b. ?b :e “E”; :f “F”. :d :f ✤ ?a :b [ :c “C” ]. D F
- 33. SELECT and more ✤ PREFIX dc: <http://purl.org/dc/elements/1.1/> ✤ SELECT ?title WHERE { <http://mybook.com> dc:title ?title.} ✤ CONSTRUCT { ?b ns:isKnownBy ?a } WHERE { ?a foaf:knows ?b } ✤ ASK { <http://kruk.me/> foaf:knows ?c } ✤ DESCRIBE ?a WHERE { ?a foaf:knows <http://kruk.me> }
- 34. SPARQL Filtering ✤ OPTIONAL { ?x ns:y ?z } ✤ FILTER ( xsd:dateTime(?date) > xsd:dateTime("2010-03-01T00:00:00Z") ) ✤ FILTER regex( ?value, "This is a S+", "i" ) ✤ isURI/isIRI, isBlank, isLiteral, sameTerm, langMatches ✤ str, lang, datatype
- 35. Python RDFLib from rdflib.graph import Graph, URIRef from rdflib.namespace import Namespace from rdflib import plugin plugin.register('sparql', rdflib.query.Processor, 'rdfextras.sparql.processor', 'Processor') plugin.register('sparql', rdflib.query.Result, 'rdfextras.sparql.query', 'SPARQLQueryResult') plugin.register('turtle', rdflib.serializer.Serializer, 'rdflib.plugins.serializers.turtle', 'TurtleSerializer') namespaces = { 'skos' : Namespace('http://www.w3.org/2004/02/skos/core#'), } def list_friends(f_name, uri): g = Graph() g.parse(f_name, format="n3") query = "SELECT ?fn WHERE { ?f foaf:knows <%s>; foaf:name ?fn. }" % uri return [ f for f in g.query(query, initNs=namespaces) ]
- 36. Read RDFa into RDF from pyRdfa import pyRdfa, Options def rdf2turtle(url): options = Options(output_processor_graph=True) turtle = pyRdfa(options=options).rdf_from_source(url, outputFormat='turtle') return turtle
- 37. Gotchas
- 38. Don’t overcomplicate ✤ Gödel’s Incompleteness Theorems ✤ First-Order Logic vs OWL-Full / CYC ✤ Jim Handler: “Little semantics go a long way” ✤ Folksonomies
- 39. OOP vs Description Logic ✤ B rdfs:subClassOf A C rdfs:domain A D rdfs:domain B ✤ Infers: ✤ C rdfs:domain B [WRONG!] ✤ D rdfs:domain A [OK]
- 40. OOP vs Description Logic ✤ B rdfs:subClassOf A C rdfs:domain A D rdfs:domain B domain A C ✤ Infers: subClassOf domain B D ✤ C rdfs:domain B [WRONG!] ✤ D rdfs:domain A [OK]
- 41. Open World Assumptions ✤ RDF is by it’s virtue a distributed being ✤ You might only have a part of it ✤ The rest is on Linked Data ✤ Unlike in the close world assumption reasoning, if there is no statement “Sebastian isFrom Poland” it does not mean, I am not.
- 42. RDBMS and NoSQL vs RDF ✤ We can store RDF in RDBMS; even easier in NoSQL ✤ Certain SPARQL path queries can be translated to SQL ✤ Usually no joint queries NoSQL ➡ DIY path querying
- 43. How can web semantics help ✤ interoperability ✤ information retrieval ✤ recommendations and matchmaking ✤ SEO
- 44. Linked Data is King Dr. Sebastian Ryszard Kruk CTO/CRO Knowledge Hives sp. z o.o., sebastian@kruk.me