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2 December 2005
Web Information SystemsSemantic Web
Prof. Beat SignerProf. Beat Signer
Department of Computer Science
Vrije Universiteit Brussel
http://www.beatsigner.com
Beat Signer - Department of Computer Science - [email protected] 2November 28, 2014
The Semantic Web
I have a dream for the Web [in which com-
puters] become capable of analyzing all the
data on the Web – the content, links, and
transactions between people and computers.
A 'Semantic Web', which should make this
possible, has yet to emerge, but when it
does, the day-to-day mechanisms of trade,
bureaucracy and our daily lives will be
handled by machines talking to machines.
The 'intelligent agents' people have touted
for ages will finally materialize.Weaving the Web - The Original Design and Ultimate Destiny of the World Wide Web by Its Inventor,
Tim Berners-Lee, Harper San Francisco, September 1999
Tim Berners-Lee
Beat Signer - Department of Computer Science - [email protected] 3November 28, 2014
The Semantic Web ...
The Semantic Web is a vision: the idea of having data on
the Web defined and linked in a way that it can be used by
machines not just for display purposes, but for auto-
mation, integration and reuse of data across various
applications. Metadata provides a means to make
statements and create machine-readable statements. W3C, 2003
Beat Signer - Department of Computer Science - [email protected] 4November 28, 2014
The Semantic Web ...
Meaning of data on the Web can not only be infered by
people but also discovered by machines without (or with
less) human intervention
Web of Data instead of Web of Documents the Web as a huge decentralised database (knowledge base)
machine-accessible data
data may be interconnected similar to today's webpages
machine-readable metadata for existing web content
combination of data from different sources to derive new facts
machines (agents) may use logical reasoning to infer facts that are not explicitly recorded
Crucial component of Web 3.0 or Giant Global Graph
Beat Signer - Department of Computer Science - [email protected] 5November 28, 2014
Video: The Future Internet
Beat Signer - Department of Computer Science - [email protected] 6November 28, 2014
Semantic Web Stack
The Semantic Web Stack
(or Semantic Web Cake)
describes the architecture
of the Semantic Web
URI/IRI
- unique identification of semantic
web resources
Unicode
- representing/manipulating text
in different languages
XML
- interchange of structured data
over the Web
Character set: UNICODE
Cry
pto
gra
ph
y
Syntax: XML and XML Namespaces
Data interchange: RDF
Taxonomies: RDFS
Ontologies: OWLQuerying:
SPARQL
Unifying Logic
Trust
User interface and applications
Proof
Rules:RIF/SWRL
Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png]
Identifiers: URI/IRI
Beat Signer - Department of Computer Science - [email protected] 7November 28, 2014
Semantic Web Stack ...
XML Namespaces
- uniquely qualify markup from
multiple sources (integration)
Resource Description
Framework (RDF)
- define RDF triples and repre-
sent resource information in
a graph structure
RDF Schema (RDFS)
- create hierarchies of classes
and properties
Character set: UNICODE
Cry
pto
gra
ph
y
Syntax: XML and XML Namespaces
Data interchange: RDF
Taxonomies: RDFS
Ontologies: OWLQuerying:
SPARQL
Unifying Logic
Trust
User interface and applications
Proof
Rules:RIF/SWRL
Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png]
Identifiers: URI/IRI
Beat Signer - Department of Computer Science - [email protected] 8November 28, 2014
Semantic Web Stack ...
Web Ontology Language
(OWL)
- language to define vocabularies
- extends RDFS with more ad-
vanced features (e.g. cardinality)
- enables reasoning based on
description logic
SPARQL
- query language to query any
RDF-based data
Rule Interchange Format
(RIF) and Semantic Web
Rule Language (SWRL)
- describe relations that cannot be
described in OWL
Character set: UNICODE
Cry
pto
gra
ph
y
Syntax: XML and XML Namespaces
Data interchange: RDF
Taxonomies: RDFS
Ontologies: OWLQuerying:
SPARQL
Unifying Logic
Trust
User interface and applications
Proof
Rules:RIF/SWRL
Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png]
Identifiers: URI/IRI
Beat Signer - Department of Computer Science - [email protected] 9November 28, 2014
Semantic Web Stack ...
Unifying Logic
- logical reasoning (infer new
facts and check consistency)
Proof
- explain logical reasoning steps
Cryptography
- protect RDF data via encryption
- validate the source of facts by
digitally signing RDF data
Trust
- authentification of sources and
trustworthiness of derived facts
User Interface
- user interfaces for semantic web
applications
Character set: UNICODE
Cry
pto
gra
ph
y
Syntax: XML and XML Namespaces
Data interchange: RDF
Taxonomies: RDFS
Ontologies: OWLQuerying:
SPARQL
Unifying Logic
Trust
User interface and applications
Proof
Rules:RIF/SWRL
Based on [http://en.wikipedia.org/wiki/File:Semantic-web-stack.png]
Identifiers: URI/IRI
Beat Signer - Department of Computer Science - [email protected] 10November 28, 2014
Resource Description Framework
The Resource Description Framework (RDF) has
been designed to describe data and metadata about specific subjects
structure of data sets
relationships between bits of data
An RDF statement (triple) consists of three parts subject
predicate (property)
object (value)
{person-1, name, "Niklaus Wirth"}
subject predicate object
Beat Signer - Department of Computer Science - [email protected] 11November 28, 2014
Resource Description Framework ...
Subjects, predicates and objects are all resources
Resource anything that can be referenced by a URI
Literal non-structured data (e.g. String, Integer, ...); is also a resource
a literal cannot be the subject of an RDF statement
Predicate relation between two resources or between a resource and a
literal
RDF data is often stored in relational databases or so-
called triplestores (e.g. Apache Jena) up to billions of triples
Beat Signer - Department of Computer Science - [email protected] 12November 28, 2014
RDF Graph
A set of RDF statements can be represented as a
directed labelled graph note that in RDF we can only define statements about specific
instances but not about generic concepts
- ontologies have to be used to define statements about generic concepts
Beat
SignerhasFamilyName
hasGivenName
http://wise.vub.ac.be/beat-signer
Beat Signer - Department of Computer Science - [email protected] 13November 28, 2014
RDF Graph ...
Anonymous resources have no explicit identifier in the example, the "office" is an anonymous resource
anonymous resources are also called blank nodes or bnodes
blank nodes can only be used as subjects or objects
Beat Signer
hasFamilyNamehasGivenName
http://wise.vub.ac.behasDirector
http://wise.vub.ac.be/beat-signer
isMember
Lode
http://wise.vub.ac.be/lode-hoste
Hoste
hasFamily
Name
hasGivenName
isColleague
hasOffice
10F733 026293306
room phone
Beat Signer - Department of Computer Science - [email protected] 14November 28, 2014
RDF Reification
An RDF triple is not a resource and can therefore not
become subject of another statement we have to reify the original statement
- make a resource out of the statement
Beat Signer
hasFamilyNamehasGivenName
http://wise.vub.ac.behasDirector
http://wise.vub.ac.be/beat/
isMember
Lode
http://wise.vub.ac.be/lode/
Hoste
hasGivenName
rdf:subject rdf:object
rdf:statement isColleague
rdf:type
rdf:Property
1
forYears
hasFamily
Name
Beat Signer - Department of Computer Science - [email protected] 15November 28, 2014
RDF Container Nodes
Special container resource types bag
- number of unordered resources with potential duplicates
sequence
- ordered collection of resources
alternative
- one of the members can be selected
collection
- closed; once it has been defined, the
members can no longer be changed
http://wise.vub.ac.be/beat-signer
wearsShirt
http://shirt.org/shirt1
http://shirt.og/shirt2RDF:_2
rdf:alternative
Beat Signer - Department of Computer Science - [email protected] 16November 28, 2014
Advantages of RDF
Simple
Enables the combination (merging) of data from
different data models not easily possible in a relational database (different schemas)
The same resource can be annotated by different people resource referenced by URI
separation of data and metadata
Well-defined standard many tools available
- triplestores, parsers, editors, frameworks, ...
Beat Signer - Department of Computer Science - [email protected] 17November 28, 2014
RDF Schema (RDFS)
Vocabulary description language for RDF domain vocabulary and structure
Define common concepts and relationships classes (rdfs:Class) and subclasses (rdfs:subClassOf)
properties and sub-properties (rdfs:subPropertyOf)
domain (rdfs:domain) and range (rdfs:range) of a property
rdfs:seeAlso, rdfs:isDefinedBy (utility properties)
rdfs:label, rdfs:comment
...
Provides the basic elements for the definition of
ontologies
Beat Signer - Department of Computer Science - [email protected] 18November 28, 2014
RDF Schema Example
Beat Signer
hasFamilyNamehasGivenName
Researcher
http://wise.vub.ac.be/beat-signer
Lode
http://wise.vub.ac.be/lode-hoste
Hoste
isColleague
hasFamilyNamehasGivenName
rdf:type rdf:type
Person isColleague
rdfs:Class rdf:Property
rdf:type rdf:typerdfs:domain
rdfs:range
rdfs:subClassOf
rdfs:Literal rdfs:Literal rdfs:Literal rdfs:Literal
rdf:type rdf:type rdf:type rdf:type
Beat Signer - Department of Computer Science - [email protected] 19November 28, 2014
Advantages of RDFS
With RDFS we have a richer expressiveness
(e.g. subClassOf) than with RDF
Simple reasoning (e.g. type hierarchy)
Many existing tools to deal with RDFS
However, some things cannot be expressed; for example "a person must have a family name"
"a person can have at most one family name" (cardinality)
"if Beat is a colleague of Lode then Lode is a colleague of Beat" (transitivity)
these issues are addressed by the Web OntologyLanguage (OWL)
Beat Signer - Department of Computer Science - [email protected] 20November 28, 2014
RDF(S) / XML Serialisation
Syntax not so easy to learn many different ways to construct the same statement
long URIs are hard to read
{http://wise.vub.ac.be/beat-signer, isColleague,http://wise.vub.ac.be/lode-hoste}
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"><rdf:Description rdf:about="http://wise.vub.ac.be/beat-signer"><isColleague rdf:resource="http://wise.vub.ac.be/lode-hoste"/><hasGivenName>Beat</hasGivenName>...</rdf:Description>...</rdf:RDF>
Beat Signer - Department of Computer Science - [email protected] 21November 28, 2014
RDF Notation 3 (N3)
Short non-XML serialisation separate predicates with a semicollon
finish subject definition with a full stop
Note that the N3 notation offers more features than are
necessary for RDF(S) serialisation e.g. support for RDF-based rules
<http://wise.vub.ac.be/beat-signer> isColleague <http://wise.vub.ac.be/lode-hoste>;...hasGivenName "Beat".
Beat Signer - Department of Computer Science - [email protected] 22November 28, 2014
RDF Turtle Notation
Terse RDF Triple Language
Subset of N3 language only describes RDF features (RDF graph model)
Syntax looks similar to Notation 3 http://www.w3.org/TeamSubmission/turtle/
Many RDF frameworks (e.g. Jena) offer Turtle parser
and serialisation features
Beat Signer - Department of Computer Science - [email protected] 23November 28, 2014
RDF Applications
Annotea project defines an RDF schema for the types of annotations that can be
used to annote webpages
RSS some RSS versions use RDF(S) / XML serialisation
Dublin Core widely used to describe digital media (also in standard HTML)
- bibliographic metadata such a title, creator, description, ...
uses RDF(S) / XML serialisation as one possible representation
<head>...<meta name="DC.Subject" content="Interactive Paper, Cross-media ..."/><meta name="DC.Description" content="Beat Signer does research on ..."/></head>
Beat Signer - Department of Computer Science - [email protected] 24November 28, 2014
SPARQL Query Language
RDF query language which can be used to extract information as URIs, literals, blank nodes or subgraphs
SPARQL SELECT queries return variable bindings
SPARQL querying relies on graph pattern matching
Example get the name and mbox of all subjects that have both of these
properties defined
SELECT ?name ?mboxWHERE { ?x foaf:name ?name .
?x foaf:mbox ?mbox }
Beat Signer - Department of Computer Science - [email protected] 25November 28, 2014
Web Ontology Language (OWL)
OWL evolved from DAML+OIL DAML is the DARPA Agent Markup Language
OIL stands for Ontology Inference Layer
There exist 3 different OWL sublanguages (flavours) with
different expressivness OWL Full
- maximum expressiveness (full language)
- no computational guarantee
OWL DL
- maximal OWL Full subset that is still computationally decidable
OWL Lite
- classification hierarchy and simple constraints (limited cardinality constraints)
- weakest of the three variants
Beat Signer - Department of Computer Science - [email protected] 26November 28, 2014
Jena Semantic Web Framework
Open source Semantic Web framework for Java create and access data from RDF graphs via an RDF API
offers an OWL API
data can be stored in files, databases or accessed via URLs
http://jena.sourceforge.net
RDF graphs can be serialised into different formats RDF/XML
Notation 3
Turtle
relational database
SPARQL query interface
Multiple reasoners
Beat Signer - Department of Computer Science - [email protected] 27November 28, 2014
Protégé
Free open source platform
to create, manipulate and
visualise ontologies
Two modelling tools
Protégé-Frames editor
- build and populate frame-based
ontologies
- Java API for plug-ins
Protégé-OWL editor
- build Semantic Web ontologies
Beat Signer - Department of Computer Science - [email protected] 28November 28, 2014
Swoogle
Search engine for seman-
tic web data (RDF)
ontologies
instance data
single terms
Ranking of semantic web
documents
inspired by Google's
PageRank
Developed at the
University of Maryland http://swoogle.umbc.edu
Beat Signer - Department of Computer Science - [email protected] 29November 28, 2014
Friend of a Friend (FOAF)
Personal information and connections to friends in RDF http://www.foaf-project.org
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" xmlns:foaf="http://xmlns.com/foaf/0.1/"><foaf:Person><foaf:name>Beat Signer</foaf:name><foaf:title>Prof.</foaf:title><foaf:givenname>Beat</foaf:givenname><foaf:family_name>Signer</foaf:family_name><foaf:nick>Beat</foaf:nick><foaf:mbox_sha1sum>ce6d419869307d57839feef6445a9d64f784eb36</foaf:mbox_sha1sum>...<foaf:knows><foaf:Person><foaf:name>Moira C. Norrie</foaf:name><foaf:mbox_sha1sum>4cb61b36a6feaa48c78acbb51fcce7cb356afdd6</foaf:mbox_sha1sum><rdfs:seeAlso rdf:resource="http://www.globis.ethz.ch/people/norrie.rdf"></foaf:Person></foaf:knows>...</foaf:Person></rdf:RDF>
Beat Signer - Department of Computer Science - [email protected] 30November 28, 2014
Friend of a Friend (FOAF) ...
First social Semantic Web application
Miller and Brickley, 2000
Describe a social network without a central database
links can be followed by
spiders (data mining)
no unique identifier
- identification by description
(pedicates and objects)
"six degrees of separation" or
"small world phenomenon"
FOAFNaut browser
[http://rdfweb.org/images/foaf/foafnaut-screenshot-path.jpg]
Beat Signer - Department of Computer Science - [email protected] 31November 28, 2014
Semantic Wikis
Use Semantic Web
technologies to provide
machine-processable
Wiki content
page content
link metadata
Ontology reasoning
much richer query interface
Existing semantic Wikis
DBPedia
Semantic MediaWiki
...
Beat Signer - Department of Computer Science - [email protected] 32November 28, 2014
Linked Data
Link different data sources (URIs) on the Web provide metadata about the resources via RDF/XML, N3, etc.
provide links to resources in other data sets on the Web
Linked Open Data community project RDF tripes from DBPedia, GeneID, ACM, etc. (>30 billion triples)
links between those triples (>500 million links)
http://lod-cloud.net/versions/2014-08-30/lod-cloud.svg
Beat Signer - Department of Computer Science - [email protected] 33November 28, 2014
Semantic Desktops
Apply Semantic Web tech-
nologies to personal infor-
mation management (PIM)
inter-application data sharing
enhancement of limited
filesystem functionality
- add document metadata
Examples
Haystack
Nepomuk
Nepomuk Integration with Dolphin (KDE 4.0)
Beat Signer - Department of Computer Science - [email protected] 34November 28, 2014
GoodRelations
Lightweight ontology for expressing
product information in e-commerce web applications
Product features offers
prices
units
...
Adopted by various companies Yahoo
BestBuy
...
Leads to enhanced product search functionality
Beat Signer - Department of Computer Science - [email protected] 35November 28, 2014
Microformats
Add semantics to (X)HTML pages
Makes use of specific (X)HTML tag attributes class and rel attributes
- e.g. rel="nofollow" for search engines
Specific microformats
hCard: contact information
hCalendar: event information
hProduct: product information
Alternative solutions semantic web (RDFa)
GRDDL
- Gleaning Resource Descriptions from Dialects of Language
- can convert from microformats to semantic web data (RDF)
Beat Signer - Department of Computer Science - [email protected] 36November 28, 2014
hCard Microformat Example
Some search engines (e.g. Google and Yahoo) start to
pay attention to different types of microformats
<head profile="http://www.w3.org/2006/03/hcard">...</head>...<div class="vcard"><div class="fn">Lode Hoste</div><div class="org">Vrije Universiteit Brussel</div><div class="tel">32 2629 3306</div><a class="url" href="http://wise.vub.ac.be/members/lode-hoste">
http://wise.vub.ac.be/members/lode-hoste</a></div>
Beat Signer - Department of Computer Science - [email protected] 37November 28, 2014
RDF in Attributes (RDFa)
Add a set of attribute extensions to XHTML for
embedding RDF metadata
Different vocabularies FOAF, video, audio, commerce, …
Search engines (e.g. Yahoo and Google) process certain
RDFa metadata (e.g. product information)
<p xmlns:dc=http://purl.org/dc/elements/1.1/about="http://www.amazon.com/...">
and the will to live. <span property="dc:creator">Simpson</span>dedicates the book <cite property="dc:title">Touching the Void</cite> tothe... The book was published in <span property="dc:date"content="1989-12-01">December 1989</span>.</p>
Beat Signer - Department of Computer Science - [email protected] 38November 28, 2014
Microdata
Add machine readable metadata (semantics) to
HTML5 documents in the form of key/value pairs can be used by crawlers, search engines (SEO) and browsers to
provide a richer browsing experience
alternative to Microformats and RDFa
W3C W
ork
ing D
raft
<section itemscope itemtype="http://data-vocabulary.org/Person">Hello, my name is <span itemprop="name">Beat Signer</span> and I am a<span itemprop="title">Professor</span> at the<span itemprop="affiliation">Vrije Universiteit Brussel. </span><section itemprop="address" itemscope itemtype="http://data-vocabulary.org/Address">My address is:<span itemprop="street-address">Pleinlaan 2</span>,<span itemprop="postal-code">1050 </span><span itemprop="locality">Brussels</span>,<span itemprop="country-name">Belgium</span>.</section></section>
Beat Signer - Department of Computer Science - [email protected] 39November 28, 2014
Exercise 9
Semantic Web working with linked data
Beat Signer - Department of Computer Science - [email protected] 40November 28, 2014
References
Tim Berners-Lee, James Hendler and Ora
Lassila, The Semantic Web, Scientific American
Magazine, May 2001 http://www.scientificamerican.com/article.cfm?id=the-semantic-web
The Future Internet: Service Web 3.0 http://www.youtube.com/watch?v=off08As3siM
Resource Description Framework (RDF) http://www.w3.org/RDF/
Thomas B. Passin, Explorer's Guide to the Semantic
Web, Manning Publications, March 2004
Beat Signer - Department of Computer Science - [email protected] 41November 28, 2014
References ...
Linked Data http://linkeddata.org
2 December 2005
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