Dr. Alexandra I. Cristea http://www.dcs.warwick.ac.uk/~acristea/

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• The internet - already there
• HTML programmers
• Search engines
• Core weight of interest
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I have a dream for the Web [in which computers] become capable of analyzing all the data on the Web –– the content, links, and transactions between people and computers.
...the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines.
Tim Berners-Lee (1999) Weaving the Web
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Scientific American, May 2001:
• Realising the complete “vision” is too hard for now
(probably)
• But we can make a start by adding semantic annotation to web resources
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[Hendler & Miller 02]
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• 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! Terminator 3 trailers!
• 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?
[Goble 03]
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Find images of Peter Patel-Schneider, Frank van Harmelen and Alan
Rector…
Rev. Alan M. Gates, Associate Rector of the
Church of the Holy Spirit, Lake Forest, Illinois
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• Complex queries involving background knowledge
– Find information about “animals that use sonar but are not either bats or dolphins”
, e.g., Barn Owl
• 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
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• Consider a typical web page:
• Markup consists of:
– rendering information
(e.g., font size and colour)
– Hyper-links to related content
• Semantic content is accessible to humans but not
(easily) to computers…
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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 7 th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event …
Speakers confirmed
Tim berners-lee
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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 7 th May Honolulu will provide
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<name> WWW2002
The eleventh international world wide webcon </name>
<location> Sheraton waikiki hotel
Honolulu, hawaii, USA </location>
<date> 7-11 may 2002 </date>
<slogan>
1 location 5 days learn interact </slogan>
<participants> Registered participants coming from australia, canada, chile denmark, france, germany, ghana, hong
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WWW2002
The eleventh international world wide webcon </conf>
Sheraton waikiki hotel
Honolulu, hawaii, USA </place>
7-11 may 2002 </date>
1 location 5 days learn interact </slogan>
<participants> Registered participants coming from australia, canada, chile denmark,
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< name > WWW2002
The eleventh international world wide webc </ name >
< location > Sheraton waikiki hotel
Honolulu, hawaii, USA </ location >
< date > 7-11 may 2002 </ date >
< slogan > 1 location 5 days learn interact </ slogan >
< participants > Registered participants coming from australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy,
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• What are you doing on Burns night?
– Google “burns”
– Wikipedia articles on Robert Burns
– Amazon listing of books by Burns
– Google Maps to look at birthplace of Burns
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Google Maps
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Combining one source with a service from another
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• A large and growing number of web data sources provide program-accessible interfaces (APIs).
• The web site http://www.programmableweb.com currently (October 2015) lists over 14123.
• Most popular Web APIs are:
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• The interfaces are non-uniform - REST, RPC
(e.g., SOAP) and hybrid
• The results are returned in variety of formats -
XML, JSON, Atom
• The data schemas tend to be providerspecific
• Militates against the development of portable, generic methods of accessing and using data.
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• 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:
“... 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.”
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…
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• Invented by Tim Berners-Lee and others.
W3C driving organisation.
– Web of machine-readable data
• What are the main aims of the SW?
– Automated query-answering
– Automated use of the data (reasoning, planning,acting, etc)
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• WWW is a web of documents
• SW is a web of data
• WWW documents are human readable
• SW data is machine readable (in theory at least)
• Shared AAA principle:
Anyone can say Anything, Anywhere.
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I don’t think [the Semantic Web is] a very good name but we’re stuck with it now. The word semantics is used by different groups to mean different things .
..I think we could have called it the Data Web. ...it connects all applications together or gives [people] access to data across the company ...
Tim Berners-Lee (2007), Interview in Business Week
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• Syntax / semantics distinction: long history in philosophy of language, linguistics, formal logic
• Syntax concerned with arrangement of symbols
• Semantics concerned with the relation between symbols strings and the world: what things actually mean.
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• Query answering:
• IBM’s Watson : beats human competitors at
Jeopardy
• but
• specifically trained for this task (including looking at decade’s worth of past Jeopardy answers)
• sort of cheating (reaction times means it always gets first go!)
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• Query answering:
• Wolfram-alpha : does complex queryanswering and solves mathematical problems
• but
• hand-curated database not the Semantic
Web
• hugely labour-intensive to develop and cannot take advantage of new knowledge
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• Query answering:
• Other systems:
– considerable progress
– current state-of-the-art is extremely useful
• but
• the general case is hard!
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• Automated use of data:
• works well in constrained circumstances:
– for example: Google maps can automatically combine information about maps, speed limits, current road usage, etc., to get estimates of journey time
• very hard in unconstrained circumstances:
– classic SW example of an automated travel agent still far from achievable
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What are the requirements of the Semantic Web?
• Large numbers of users to make their data:
– available
– in an appropriate machine-readable format
This is happening now: open government data (esp. in UK and US) and many other organisations and individuals: https://www.data.gov.uk/ https://www.data.gov/
>> find more open data repositories as homework!
• Good query-answering systems
• The ability to automatically interpret and use data
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• 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
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• Originally: a definitive account of what exists
(derived from metaphysics).
• Therefore, we can create a single ontology that describes the world –
• maybe dividing into smaller sub-ontologies as necessary.
• But this is completely misconceived!
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• Check as a homework other definitions of the word
‘ontologies’ via Google.
• Hence ‘Ontology merging’ a hot research area!
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• A way of encoding domain knowledge, linking the knowledge, which allows for reasoning with the data
• Dictionary/ Vocabulary 

Taxonomy


Ontology
• Ontologies allow for data integration and inference, for automated query-answering and automated use of data
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• data integration
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• data integration
• inference
William Burnes is the father of Robert Burns.
…
Father is a subclass of parent.
…
William
Burnes is the parent of
Robert Burns.
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• data integration
• Inference
• Automated query-answering
• Automated use of data
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Dublin Core
FOAF
TrackBack
MetaVocab
Basic Geo Vocabulary
BIO
RSS 1.0
VCard RDF
Creative Commons metadata
WOT
SIOC
GoodRelations
DOAP
Programmes Ontology
Language
RDF
OWL DL
RDF
RDF
RDF Schema
RDF
RDF Schema
RDF
RDF Schema
OWL DL
OWL DL
OWL DL
RDF Schema
OWL 2
Music Ontology
OpenGUID
Provenance Vocabulary
Pedagogical diagnosis
OWL 2
RDF Schema
OWL DL
OWL DL
DILIGENT Argumentation Ontology OWL 2
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Swoogle hits Revised
1,364,337 28 October 2006
1,194,871 27 July 2005
502,401
441,790 16 February 2002
248,130
220,228
1 February 2006
5 March 2004
6 December 2000
22 February 2001
201,786
181,962
112,216
97,292
42,911
5,000
1,442
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23 February 2004
11 April 2008
1 October 2011
5 November 2005
7 September 2009
14 February 2010
24 September 2008
25 August 2009
1 April 2012
13 September 2006 http://semanticweb.org/
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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_Elephant s weigh at least 2,000 kg
– All Elephant s are either African_Elephant s or
Indian_Elephant s
– No individual can be both a Herbivore and a Carnivore
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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
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• Given key role of ontologies in the Semantic Web, it is essential to provide tools and services to help users:
– Design and maintain high quality ontologies, e.g.:
• Meaningful — all named classes can have instances
• Correct — captured intuitions of domain experts
• Minimally redundant — no unintended synonyms
• Richly axiomatised — (sufficiently) detailed descriptions
– Store (large numbers) of instances of ontology classes, e.g.:
• Annotations from web pages
– Answer queries over ontology classes and instances, e.g.:
• Find more general/specific classes
• Retrieve annotations/pages matching a given description
– Integrate and align multiple ontologies (merging)
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Shared ontologies help to exchange data and meaning between web-based services
(Image by Jim Hendler)
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Tell me what wines I should buy to serve with each course of the following menu.
Books Agent
Wine Agent
I recommend
Chardonney or
DryRiesling
Grocery Agent
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• Provide shared data structures to exchange information between agents
• Can be explicitly used as annotations in web sites
• Can be used for knowledge-based services using other web resources
• Can help to structure knowledge to build domain models (for other purposes)
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• Wide variety of languages for “Explicit Specification”
– Graphical notations
• Semantic networks
• Topic Maps (see http://www.topicmaps.org/)
• UML
• RDF
– Logic based
• Description Logics (e.g., OIL, DAML+OIL, OWL )
• Rules (e.g., RuleML, Prolog)
• First Order Logic (e.g., KIF)
• Conceptual graphs
• (Syntactically) higher order logics (e.g., LBase)
• Non-classical logics (e.g., Flogic, Non-Mon, modalities)
– Probabilistic/fuzzy
• Degree of formality varies widely
– Increased formality makes languages more amenable to machine processing (e.g., automated reasoning)
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Many languages use “OO” model based on :
• Objects /Instances/Individuals
– Elements of the domain of discourse
– Equivalent to constants in FOL
• Types /Classes/Concepts
– Sets of objects sharing certain characteristics
– Equivalent to unary predicates in FOL
• Relations /Properties/Roles
– Sets of pairs (tuples) of objects
– Equivalent to binary predicates in FOL
• Such languages are/can be:
– Well understood
– Formally specified
– (Relatively) easy to use
– Amenable to machine processing
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• Existing Web languages extended to facilitate content description
– XML 
XML Schema ( XMLS )
– RDF 
RDF Schema ( RDFS )
• XMLS not an ontology language
– Changes format ~ DTDs (document schemas) for XML
– Adds an extensible type hierarchy
• Integers, Strings, etc.
• Can define sub-types, e.g., positive integers
• RDFS is recognisable as an ontology language
– Classes and properties
– Sub/super-classes (and properties)
– Range and domain (of properties)
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???
???
???

Semantics+reasoning

Relational Data

Data Exchange
?
?
• Relationship between layers is not clear
• OWL DL extends “DL subset” of RDF
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• Isn’t just about putting data on the Web
• It’s about making links
• Web of Hypertext -> Web of Data
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1. Use URIs as names for things.
2. Use HTTP URIs so that people can look up those names.
3. When someone looks up a URI, provide useful information, using the standards
(RDF*, SPARQL).
4. Include links to other URIs, so that they can discover more things.
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• Globally unique names
– can be created in a decentralised fashion by domain name owners;
– no central naming authority is required.
• Not just a name, but a means of accessing information describing the identified entity. (URL)
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Homepage of the Department of Computer Science http://www.dcs.warwick.ac.uk/
Homepage of Alexandra Cristea http://www2.warwick.ac.uk/fac/sci/dcs/people/Alexandra_Cristea
• These URIs point to web documents - or in the terminology of WebArch, information resources .
– by definition, all its essential characteristics can be conveyed in a message
• Web clients request a representation of a resource
• One and the same resource might have different representations; e.g., text in English, Greek, Chinese, etc.
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• HTTP clients send HTTP headers with each request to indicate what kinds of documents they prefer.
• Client can say prefers language X over Y.
• Or prefers RDF over HTML.
• Servers inspect headers and select an appropriate response.
Header of GET Requests
GET /fac/sci/dcs/people/Alexandra_Cristea HTTP/1.1
Host: www2.warwick.ac.uk
Accept: text/html, application/xhtml+xml
Accept Language: en, gr, cn
Servers Response
HTTP/1.1 200 OK
Content -Type: text/html
Content-Language: en
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• We need mechanisms to ensure that when URIs are dereferenced ,
– real-world objects are not confused with documents that describe them, and
– humans as well as machines can retrieve appropriate representations.
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• RDF is standardly used for Linked Data. Advantages include:
– Easy to insert RDF links between data from different sources .
– Information from different sources can be combined by graph merging .
– Information using different schemas can be expressed in a single graph, i.e., by mixing different vocabularies .
– Data can be tightly or loosely structured.
• Features of RDF that are avoided:
– Reification (hard to query with SPARQL)
– Collections and containers (ditto). Use multiple triples with same predicate instead.
– Blank nodes : makes merging less effective.
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• Relationship Links
– related things in other data sources.
≈ hyperlinks in a web document.
– e.g. foaf:based_neardbpedia:Edinburgh
• Identity Links
– URI aliases of other data sources for the same (realworld/abstract) object.
• Vocabulary Links
– definitions of vocabulary terms used to represent the data.
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• different URIs may refer to same real-world object.
– Standard for equivalence: http://www.w3.org/2002/07/owl#sameAs.
• Motivations for this approach:
– Different aliases can be dereferenced to different description of same
resource ( AAA principle
).
– Support provenance : trace back to publisher of URI.
– canonic > centralised naming authority > barrier to spread web of data.
• Potential problems:
– Identity may be context dependent
– Facts vs. opinions
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★
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• Structured data
– available on web (i.e. open) in many formats:
– CSV, Excel, HTML Microdata(e.g. http://schema.org/), web APIs, PDF tables (shudder), ...
• Advantages of Linked Data :
– A unifying data model (RDF)
– A standardised data access mechanism (HTTP)
– Hyperlink-based data discovery : links connect all Linked Data into a single global data space and enable Linked Data applications to discover new data sources at run-time.
– Self-descriptive data: vocabulary definitions are recoverable like other data, and vocabulary terms can be linked to one another.
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• Linked data adopts perspective of data integration .
– Not (necessarily) interested in reasoning aspect of
Semantic Web.
• http://blog.paulwalk.net/2009/11/11/linked-opensemantic/:
– Data can be open, while not being linked.
– Data can be linked, while not being open.
– Data which is both open and linked is increasingly viable.
– The Semantic Web can only function with data which is both open and linked.
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• Linked Data principles
– Naming things with URIs
– Making URIs dereferenceable
– Providing useful RDF information
– Including links to other things
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Thanks to various people from whom I “borrowed” material:
– Jeen Broekstra
– Carole Goble
– Frank van Harmelen
– Austin Tate
– Raphael Volz
And thanks to all the people from whom they borrowed it

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• Course website and recommended reading
• Do your homeworks!
• There is lots of relevant literature online – try to explore it
• Also a lot of informal discussion on Twitter, newsgroups, YouTube, etc.
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