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The Semantic Web
Web Science Systems DevelopmentSpring 2015
AgendaHistory / Background
Linked Data
RDF
SPARQL
OWL
Applications
Current state of the Semantic Web
The WebCore Principles
Standard for identifying resources
Standard for representing resources
Standard for exchanging resources
The WebCore Principles
Standard for identifying resources
Standard for representing resources
Standard for exchanging resources
Standards:
URIs (URLs): Uniform Resource Identifier (Locator)
HTML: Hypertext Markup Language
HTTP: Hypertext Transfer Protocol
URI Identifies one resource
A resource could be anything
URIs are persistent
URLs also locate and are
aligned with protocols URLs are dereferenceable
URLs
mailto:[email protected]
ftp://example.org/aDirectory/aFile
ldap://ldap.example.org/c=GB?objectClass?one
HTML It is not the resource
Serialization of information
A resource can have multiple
representations
Manifestation of the resource as
a digital document Retrievable resources:
Encode data and information Link to other resources (creating the “Web”)
HTTPProtocol for information exchange on the web
Protocol is specified in the URL
Used for client-server communication (request-response protocol)
Structured text (header, body,…)
Currently at http/1.1 (since 1999), http/2 in draft form
One Web
Principles of a healthy webIdentify resources using URIs
Use HTTP in URIs so that people can look up resources
When someone looks up a resource, return useful information (using standard representation e.g. HTML)
Link to other URIs
LinkingAsserts relevance/quality of page
Allows discovery
Creates the “Web” effect
The Semantic WebWhat is it?
Semantics, knowledge representation, ontologies and agents.
Linked DataFrom the web of documents to the web of data
Documents VS. Data
Web of documents
HTML Data
HTML Data
HTML Data
HTMLData
HTMLData
Web of data
Data
Data
Data
Data
Data
Data
One Web
RDFResource Description Framework
Semantic Web Stack
RDF: Resource Description Framework
The triple
Subject ObjectPredicate
RDF: Resource Description Framework
The triple
Subject ObjectPredicate
“WebSci” “Ahmed”“hasTA”
RDF Triple
Subject Predicate Object
IRI Literal
Resource
denotes
denotes denotes
Blank Node
representedBy representedB
y
representedBy
RDF triple
“article”“James
Hendler”
“hasCreator”
http://dx.doi.org//10.1109/MC.2009.30
http://dbpedia.org/resource/
James_Hendler
http://purl.org/dc/elements/1.1/creator
RDFA triple is true if the relationship holds between the
subject and the object
ResourceCan be ‘anything’, including documents, people,
physical objects, and abstract concepts
IRI: Internationalized Resource Identifier IRIs conform to Universal Character Set, not just
ASCII IRIs are global, dereferenceable and persistent
Blank nodes are anonymous resources
RDFGraph-based Data Model
Visualized as diagram of nodes and directed-arcs
Nodes represent ‘entities’ and are resourcesArcs represent relationships between the
nodes and are also resources
RDF Graph consists of a set of triples
RDF Graph
Raw RDF
RDF Serializations (representations)Multiple serializations
RDF/XML
JSON-LD Turtle family
Turtle
N3 Trig
RDF/XML
JSON-LD
N3
RDFa
Querying RDFHow to retrieve linked data?
How and where to query RDF graphs?
SPARQLSPARQL Protocol and RDF Query Language
Semantic Web Stack
SPARQLLanguage for querying RDF
Triplestores and endpoints
Queries consist of triple patterns, conjunctions, disjunctions and optional patterns
SPARQL is a protocol that defines how an endpoint responds to a query
SPARQL query (basic)PREFIX geo: <http://www.opengis.net/ont/geosparql#>PREFIX geof: <http://www.opengis.net/def/function/geosparql/>PREFIX sf: <http://www.opengis.net/ont/sf#>PREFIX vocab: <http://localhost:2020/resource/vocab/>PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>PREFIX rpi: <http://openmap.rpi.edu#>
SELECT DISTINCT ?professor ?course ?buildingWHERE {
?prof a rpi:Professor. ?course rpi:instructedBy ?professor. ?course rpi:courseTitle ?title.
?course rpi:hostedInBuilding ?building. ?building rdfs:label ?label.
FILTER regex(?title,"WEB") }
Namespaces
Patterns to match
Filter
Variables
SPARQL query result
SPARQL query (complex)Federated query + GeoSPARQL
PREFIX geo: <http://www.opengis.net/ont/geosparql#>
PREFIX geof: <http://www.opengis.net/def/function/geosparql/>
PREFIX sf: <http://www.opengis.net/ont/sf#>
PREFIX vocab: <http://localhost:2020/resource/vocab/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rpi: <http://openmap.rpi.edu#>
SELECT DISTINCT ?professor ?course ?building
WHERE {
?course vocab:rpi_class_schedule_all_building_id ?building.
SERVICE <http://localhost:8080/parliament/sparql> {
?professor a rpi:Professor.
?course rpi:instructedBy ?professor.
?building rdfs:label ?label.
?building geo:hasGeometry ?geo.
?geo geo:asWKT ?xy
FILTER(geof:sfIntersects(?xy,"POINT(-73.681948 42.730076)" ^^<http://www.opengis.net/ont/sf#wktLiteral>))
}}
‘Remote’ Endpoint
GeoSPARQL Function
SPARQL query (complex) result
SPARQL query (inference)PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX rpi: <http://openmap.rpi.edu#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?s
WHERE {
?s a rpi:Person.
?s foaf:knows <http://openmap.rpi.edu#Ahmed_Eleish>
}
Superclass
SPARQL query (inference) result
OWLWeb Ontology Language
Semantic Web Stack
Web Ontology Language Provides semantics/structure to RDF
Computational logic-based language, allows reasoning by computer programs to:Verify consistency of knowledgeMake implicit knowledge explicit
Enables inference of new triples from existing ones
Used to build ontologies/vocabularies
Rules that constrain relationships between entities in a domain
OWL basic notionsAxioms
Entities
Expressions
OWL componentsClass hierarchies
Object properties
Property hierarchies
Domain & range restrictions
Datatypes
RPI Campus Ontology
Ontology Engineering
Expressivity
Implementation
Maintenance
Query Rules
Infer
Applications of Linked Data
Linking related dataWebsites with related data on different platforms
Linking related dataWebsites with related data on different platforms
RDBWebsite
A
Website B
Triplstore
Mapping File
RDF
SPARQL-to-SQL
Direct Mapping
XML
XSLT
RPI campus map applicationMap of the RPI campus with clickable features
(buildings, emergency callboxes,…etc.)
Geolocation data in KML for projection and in RDF for GeoSPARQL queries
Class schedule scraped off SIS in RDBMS
Mapping of schedule to RDF for SPARQL queries
Campus map KML
Campus map RDF
Class schedule
RPI campus map applicationHTML/JavaScript front-end
PHP back-end
OpenLayers 3 mapping API
OpenStreetMap tiles
Class schedule csv loaded into MySQL
D2RQ server mapping MySQL to RDF
Map data RDF loaded into Parliament triplestore
RPI Campus Map
Current state of the Semantic Web
Evolution of the web
Linked Open Data (2007)
Linked Open Data (2008)
Linked Open Data (2009)
Linked Open Data (now)
Open linked data
References Tim Berners Lee’s proposal - http://info.cern.ch/Proposal.html
W3C web architecture - http://www.w3.org/TR/webarch/
W3C Technology Stack - http://www.w3.org/Consortium/techstack-desc.html
Google PageRank - http://en.wikipedia.org/wiki/PageRank
Scientific American – The Semantic Web -http://www.cs.umd.edu/~golbeck/LBSC690/SemanticWeb.html
RDF – Resource Description Framework - http://www.w3.org/TR/rdf11-concepts/
SPARQL – SPARQL Protocol & RDF Query Language - http://www.w3.org/TR/sparql11-protocol/
OpenStreetMap - http://www.openstreetmap.org/
Parliament Triplestore - http://parliament.semwebcentral.org/
D2R Server - http://d2rq.org/
Linked Open Data - http://lod-cloud.net/
