1. CSIT600f: Introduction to Semantic Web
Dickson K.W. Chiu
PhD, SMIEEE
Text: Antoniou & van Harmelen: A Semantic Web Primer
Ref: Ivan Herman: Tutorial on Semantic Web Technology

2. Towards a Semantic Web WWW is an impressive success:
amount of available information (> 1 Giga-page)
number of human users (> 200 Mega-user)
The current Web represents information using
natural language (English, Hungarian, Chinese,…)
graphics, multimedia, page layout
Humans can process this easily
can deduce facts from partial information
can create mental associations
are used to various sensory information
(well, sort of… people with disabilities may have serious problems on the Web with rich media!)
Dickson Chiu 2006

3. Need for understanding Web info
Tasks often require to combine data on the Web:
hotel and travel infos may come from different sites
searches in different digital libraries
etc.
Again, humans combine these information easily
even if different terminologies are used!
Dickson Chiu 2006

4. However… However: machines are ignorant! …
partial information is unusable
difficult to make sense from, e.g., an image
drawing analogies automatically is difficult
difficult to combine information
is <foo:creator> same as <bar:author>?
how to combine different XML hierarchies? …
Dickson Chiu 2006

5. Example: Searching The best-known example…
Google et al. are great, but there are too many false hits
adding descriptions to resources should improve this
Dickson Chiu 2006

6. Where we are Today: the Syntactic Web
[Hendler & Miller 02]
Dickson Chiu 2006

7. The Syntactic Web is… A hypermedia, a digital library
A library of documents called (web pages) interconnected by a hypermedia of links
A database, an application platform
A common portal to applications accessible through web pages, and presenting their results as web pages
A platform for multimedia
BBC Radio 4 anywhere in the world!
Peer-to-peer sharing (BT, edonkey, PPLive, …)
A naming scheme
Unique identity for those documents
A place where computers do the presentation (easy) and people do the linking and interpreting (hard).
Why not get computers to do more of the hard work?
Dickson Chiu 2006

8. Hard using the Syntactic Web…
Finding the image of something
Find pictures that contain red birds with blue background
Complex queries involving background knowledge
Find information about “animals that use sonar but are not either bats or dolphins”
Locating information in data repositories
Travel enquiries
Prices of goods and services
Results of human genome experiments
Finding and using “web services”
Visualise surface interactions between two proteins
Delegating complex tasks to web “agents”
Book me a holiday next weekend somewhere warm, not too far away, and where they speak French or English
Dickson Chiu 2006

9. What is the Problem? Consider a typical web page: Markup comprise
rendering information (e.g., font size and colour)
Hyper-links to related content
Semantic content is accessible to humans but not (easily) to computers…
Consider a typical web page:
Dickson Chiu 2006

10. What information can we see…
WWW2002
The eleventh international world wide web conference
Sheraton waikiki hotel
Honolulu, hawaii, USA
7-11 may 2002
1 location 5 days learn interact
Registered participants coming from
australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire
Register now
On the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event …
Speakers confirmed
Tim berners-lee
Tim is the well known inventor of the Web, …
Ian Foster
Ian is the pioneer of the Grid, the next generation internet …
Dickson Chiu 2006

11. Information a machine may see…
WWW2002
The eleventh international world wide web conference
Sheraton waikiki hotel
Honolulu, hawaii, USA
7-11 may 2002
1 location 5 days learn interact
Registered participants coming from
australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire
Register now
On the 7th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event …
Speakers confirmed
Tim berners-lee
Tim is the well known inventor of the Web, …
Ian Foster
Ian is the pioneer of the Grid, the next generation internet …
Dickson Chiu 2006

12. Solution: XML markup with “meaningful” tags?
<name>WWW2002
The eleventh international world wide webcon</name>
<location>Sheraton waikiki hotel
Honolulu, hawaii, USA</location>…
How about…
<conf>WWW2002
The eleventh international world wide webcon</conf>
<place>Sheraton waikiki hotel
Honolulu, hawaii, USA</place>
Then how about…
<会议>WWW2002
The eleventh international world wide webcon</会议>
<地点>Sheraton waikiki hotel
Honolulu, hawaii, USA</地点>
Dickson Chiu 2006

13. What Is Needed? A resource should provide information about itself
also called “metadata”
metadata should be in a machine processable format
agents should be able to “reason” about (meta)data
metadata vocabularies should be defined
Dickson Chiu 2006

14. What Is Needed (Technically)?
To make metadata machine processable, we need:
unambiguous names for resources (URIs)
a common data model for expressing metadata (RDF)
and ways to access the metadata on the Web
common vocabularies (Ontologies)
The “Semantic Web” is a metadata based infrastructure for reasoning on the Web
It extends the current Web (and does not replace it)
Dickson Chiu 2006

15. Adding “Semantics” External agreement on meaning of annotations
E.g., Dublin Core (
Agree on the meaning of a set of annotation tags
Problems with this approach
Inflexible
Limited number of things can be expressed
Use Ontologies to specify meaning of annotations
Ontologies provide a vocabulary of terms
New terms can be formed by combining existing ones
Meaning (semantics) of such terms is formally specified
Can also specify relationships between terms in multiple ontologies
Dickson Chiu 2006

16. History of the Semantic Web
Web was “invented” by Tim Berners-Lee (amongst others), a physicist working at CERN
TBL’s original vision of the Web was much more ambitious than the reality of the existing (syntactic) Web:
TBL (and others) have since been working towards realising this vision, which has become known as the Semantic Web
E.g., article in May 2001 issue of Scientific American…
“... a goal of the Web was that, if the interaction between person and hypertext could be so intuitive that the machine-readable information space gave an accurate representation of the state of people's thoughts, interactions, and work patterns, then machine analysis could become a very powerful management tool, seeing patterns in our work and facilitating our working together through the typical problems which beset the management of large organizations.”
Dickson Chiu 2006

17. Berner-Lee’s Architecture
???
 Semantics+reasoning ?
 Relational Data ?
 Data Exchange
Relationship between layers is not clear
OWL DL extends “DL subset” of RDF
Dickson Chiu 2006

18. Disjointness, Inverse, part-of…
A Spectrum of Ontology
Thesauri
“narrower
term”
relation
Frames
(properties)
Formal
is-a
General
Logical
constraints
Catalog/ ID
Informal
is-a
Formal
instance
Disjointness, Inverse, part-of…
Terms/
glossary
Value Restrs.
Dickson Chiu 2006

19. Ontology: Origins and History
Ontology in Philosophy - a philosophical discipline—a branch of philosophy that deals with the nature and the organization of reality
Science of Being (Aristotle, Metaphysics, IV, 1)
studies being or existence as well as the basic categories thereof
trying to find out what entities and what types of entities exist
has strong implications for the conceptions of reality.
Dickson Chiu 2006

20. Ontology in Linguistics
Referent
Form
Stands for
Relates to
activates
Concept
[Ogden, Richards, 1923] ?
“Tank“
Dickson Chiu 2006

21. Ontology in Computer Science
An ontology is an engineering artifact [Neches91]:
defines basic terms and relations comprising the vocabulary of a topic area
the rules for combining terms and relations to define extensions to the vocabulary
“An explicit specification of a conceptualization” [Gruber93]
Formal specification of a shared conceptualization (of a certain domain) [Borst 97]:
Shared understanding of a domain of interest
Formal and machine manipulable model of a domain of interest
Dickson Chiu 2006

22. Structure of an Ontology
Ontologies typically have two distinct components:
Names for important concepts in the domain
Elephant is a concept whose members are a kind of animal
Herbivore is a concept whose members are exactly those animals who eat only plants or parts of plants
Adult_Elephant is a concept whose members are exactly those elephants whose age is greater than 20 years
Background knowledge/constraints on the domain
Adult_Elephants weigh at least 2,000 kg
All Elephants are either African_Elephants or Indian_Elephants
No individual can be both a Herbivore and a Carnivore
Dickson Chiu 2006

23. Ontology Elements Concepts (classes) + their hierarchy
Concept properties (slots / attributes)
Property restrictions (type, cardinality, domain, etc.)
Relations between concepts (disjoint, equality, etc.)
Instances
E-R diagram / UML diagram ???
Note: “Property”  “Slot”  “Relation”  “Relationtype”  “Attribute”  Semantic link type”
Dickson Chiu 2006

24. A Semantic Web — First Steps
Make web resources more accessible to automated processes
Extend existing rendering markup with semantic markup
Metadata annotations that describe content/function of web accessible resources
Use Ontologies to provide vocabulary for annotations
“Formal specification” is accessible to machines
A prerequisite is a standard web ontology language
Need to agree common syntax before we can share semantics
Syntactic web based on standards such as HTTP and HTML
Dickson Chiu 2006

25. More Example: Automatic Assistant
Your own personal (digital) automatic assistant
knows about your preferences
builds up knowledge base using your past
can combine the local knowledge with remote services:
hotel reservations, airline preferences
dietary requirements
medical conditions
calendaring
etc
It communicates with remote information (i.e., on the Web!)
Dickson Chiu 2006

26. Example: Database Integration
Databases are very different in structure, in content
Lots of applications require managing several databases
after company mergers
combination of administrative data for e-Government
biochemical, genetic, pharmaceutical research
etc.
Most of these data are now on the Web
The semantics of the data(bases) should be known
how this semantics is mapped on internal structures is immaterial
Dickson Chiu 2006

27. Example: Digital Libraries
It is a bit like the search example
It means catalogs on the Web
librarians have known how to do that for centuries
goal is to have this on the Web, World-wide
extend it to multimedia data, too
But it is more: software agents should also be librarians!
help you in finding the right publications
Dickson Chiu 2006

28. Example: Semantics of Web Services
Web services technology is great
But if services are ubiquitous, searching issue comes up, for example:
“find me the most elegant Schrödinger equation solver”
what does it mean to be
“elegant”?
“most elegant”?
mathematicians ask these questions all the time…
It is necessary to characterize the service
not only in terms of input and output parameters…
…but also in terms of its semantics
Dickson Chiu 2006

29. How Simple Ontologies Help
not as costly to build and potentially
more importantly, many are available
provide a controlled vocabulary
website organization and navigation support
support expectation setting (e.g. user interface)
“umbrella” structures from which to extend content (e.g., UNSPSC)
searching support
sense disambiguation support (e.g., terms belong to different categories)
Deborah McGuinness. Ontologies Come of Age. The Semantic Web: Why, What and How, MIT Press, (MS-Word)
Dickson Chiu 2006

30. How Structured Ontologies Help
more structure => more power
consistency checking
completion (of unspecified attributes and relations)
interoperability support
validation and verification testing or even encode entire test suites
structured, comparative, and customized search
“intelligence” in application, e.g., system configuration support
Dickson Chiu 2006

31. Benefits of Semantic Web
Communication between people
Interoperability between software agents
Reuse of domain knowledge
Make domain knowledge explicit
Analyze domain knowledge
Dickson Chiu 2006

32. The Semantic Web is Not “Artificial Intelligence on the Web”
although it uses elements of logic…
… it is much more down-to-Earth (we will see later)
it is all about properly representing and characterizing metadata
of course: AI systems may use the metadata of the SW
but it is a layer way above it
“A purely academic research topic”
SW is out of the university labs now
lots of applications exist already (see examples later)
big players of the industry use it (Sun, Adobe, HP, IBM,…)
of course, much is still be done!
Building an ontology is not a goal in itself
Dickson Chiu 2006