Semantic Web

1
Semantic Web

• Steve Cayzer, Hewlett-Packard Laboratories
• Guest Lecture for Nottingham University
• 12 March 2004

2
Introduction

• HTML for presentation
• XML for data
• RDF for meaning

A new form of Web content that is meaningful to
computers will unleash a revolution of new
possibilities
3
The Official Definition
Definition The Semantic Web is the
representation of data on the World Wide Web. It
is a collaborative effort led by W3C with
participation from a large number of researchers
and industrial partners. It is based on the
Resource Description Framework (RDF), which
integrates a variety of applications using XML
for syntax and URIs for naming.

• http//www.w3.org/2001/sw/

4
The current web is not enough

• Homogeneous resources
• Semantically empty
• Needs human interpretation

5
Why do we care?

• Data integrationBuilding a global knowledge
  base
• Knowledge managementDecentralized Aggregation
• Social networksAnalysing community structures
• Intelligent web searchFind the concept not the
  keyword

6
Why do we care?

• Data integrationBuilding a global knowledge
  base
• Knowledge managementDecentralized Aggregation
• Social networksAnalysing community structures
• Intelligent web searchFind the concept not the
  keyword

7
Its about the data, stupid
Sean Palmer The Semantic web is a mesh of
information linked up in such a way as to be
easily processable by machines, on a global
scale. You can think of it as being an efficient
way of representing data on the World Wide Web,
or as a globally linked database.
Aaron Swartz the idea is to get everyone sharing
their vast databases of information in RDF with
each other. Then we can write programs that put
this data together to answer questions and take
actions to make our lives easier.
8
Core concepts

• URIs You must name something before you can use
  it
• Triples subject, predicate, object. The basis
  for all communication!
• RDF Model Nodes and arcs
• RDF serialization Graph, RDF/XML, N3
• Ontologies RDF Schema, OWL

9
RDF is not XML, though it can be expressed in XML

• The semantic web is about data modelling
• RDF describes this model
• The model can be expressed in XML (or N3, or
  drawn as a graph)
• XML Schema is all about syntax and so has limited
  use for RDF
• RDF Schema is all about the model

10
The semantic web stack
11
FOAFa semweb case study
The Friend of a Friend (FOAF) project is about
creating a Web of machine-readable homepages
describing people, the links between them and the
things they create and do. Distributed RDF/XML
records describing people, who they know,
projects they work on
12
FOAF - motivations

• Augment e-mail filtering by prioritizing mails
  from trusted colleagues
• Locate people with interests similar to yours
• Find an expert in knowledge communities
• Social network analysis
• Photo co-depiction

13
A simple foaf model
foafPerson
rdftype
foafname
Michael Souris
foafmbox
mailtomm_at_example.com
14
.. which can be serialized in XML
df-syntax-ns" xmlnsfoaf"http//xmlns.com/foaf/
0.1/" Michael
Souris rdfresource"mailtomm_at_example.com" /

15
.. and N3
_at_prefix rdf tax-ns _at_prefix foaf
a foafPerson foafname Michael Souris
foafmbox .
16
A more complex foaf model
foafPerson
foafPerson
rdftype
rdftype
foafname
foafname
foafknows
Donald Canard
Michael Souris
foafmbox
foafmbox
mailtomm_at_example.com
mailtodd_at_example.com
17
A more complex foaf example
Michael
Souris rdfresource"mailtomm_at_example.com"
/
ple.com" / Donald
Canard

18
Moving on up RDFS and OWL

• RDF Schema (RDFS) for class and property
  hierarchies, domain and range
• Web Ontology Language (OWL) extends RDF Schema to
  allow ontologies with more complex relationships
• limit the properties of classes with respect to
  number and type
• means to infer that items with various properties
  are members of a particular class
• a well-defined model for property inheritance

19
Inferencing

• If-then rules
• RDFS
• relfriendOf rdfssubPropertyOf foafknows .
• OWL
• foafmbox rdftype
  .
• Historical note DAMLOIL

20
Semantic web related technologies

• Topic mapsAlternative data model to RDF
• XFMLFacet Mapping in XML
• UMLTraditional modelling maps to RDF
• Description LogicTheoretical basis for RDF models

21
Take home message

• The semantic web is about globally sharing,
  processing and integrating information.
• RDF is a model.
• RDF is not XML, though it may be serialized in
  XML
• Not everyone believes in the semantic web.
  Everybody believes in XML.

22
Questions

• (Resources follow check handouts)

23
Resources tutorials

• Official page http//www.w3.org/2001/sw/
• RDF primer http//www.w3.org/TR/2004/REC-rdf-prime
  r-20040210/
• N3 primer http//www.w3.org/2000/10/swap/Primer
  and http//www.w3.org/2000/10/swap/doc/
• OWL guide http//www.w3.org/TR/2004/REC-owl-guide-
  20040210/
• Sean Palmer programmers intro (2001) dated but
  quite nice http//infomesh.net/2001/swintro/
• Morbus Iff (creator of Amphetadesk) The Semantic
  Web 1-2-3 good overview http//disobey.com/deterg
  ent/2002/sw123/

24
Resources - books

• Practical RDF. (2003) RDF/XML focused but well
  written and highly recommended http//www.oreilly.
  com/catalog/pracrdf/
• The Semantic Web A Guide to the Future of XML,
  Web Services and Knowledge Management  Michael C.
  Daconta et al. Complementary alternative
  http//www.amazon.co.uk/exec/obidos/ASIN/047143257
  1/
• Knowledge Transformation for the Semantic Web
  Omelayenko Klein. (Much) more advanced
  http//www.amazon.co.uk/exec/obidos/ASIN/047143257
  1  

25
Resources - articles

• See list of W3C articles http//www.w3.org/2001/sw
  /pub
• But especially
• The Semantic Web, Scientific American, May 2001,
  Tim Berners-Lee, James Hendler and Ora Lassila
• Integrating applications on the Semantic WebJim
  Hendler, Tim Berners-Lee and Eric Miller, Journal
  IEE Japan, 122(10)676-680, 2002.

26
Resources software tools

• Jena the swiss army knife of the semantic
  web, produced by Hewlett-Pckard Laboratories in
  Bristol and Palo Altohttp//www.hpl.hp.com/semweb
  /jena.htmTry the Jena tutorial to get a first
  introduction to semweb developmenthttp//jena.sou
  rceforge.net/tutorial/RDF_API/index.html
• Protégé Easy ontology creation, from Stanford
  Universityhttp//protege.stanford.edu/
• TAP semantically assisted Google!http//tap.sta
  nford.edu/ Online demo at http//ontap.stanford.e
  du/sail

27
Resources interviews and presentations

• W3C list http//www.w3.org/2001/sw/events
• Aaron Swartz interview January 23 2004
  http//iron.wootest.net/aaron_swartz.php
• Eric Miller (W3C semantic web activity lead)
  talk, early 2004http//www.w3.org/2004/Talks/0120
  -semweb-umich/slide1-0.html
• The Semantic Web, Tim Berners-Lee 2002

28
Additional Slides