Semantic Web

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Semantic Web
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What is semantic web?
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What is semantic web

• "The Semantic Web is an extension of the current
  web in which information is given well-defined
  meaning, better enabling computers and people to
  work in cooperation."
• -- Tim Berners-Lee, James Hendler, Ora
  Lassila, The Semantic Web, Scientific American,
  May 2001
• 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 automation, integration and
  reuse of data across various applications.
• --W3C 2003

Scientific American, May 2001
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Todays Web

• What we use todays web for
• Browse (our course web site)
• Search (Google)
• B2C (Amazon)
• B2B

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Search

• High recall, low precision
• Searching for semantic web in google returns
  10,800,000 pages (in 2005).
• Results are highly sensitive to vocabulary
• If you search for faculty member, you wont be
  able to find professors.
• Results are single web pages
• You will not be able to find professors who are
  teaching semantic web in Canada
• Current search engines cant integrate related
  web pages in different places

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B2C E-Commerce

• A typical scenario user visits one or several
  online shops, browses their offers, selects and
  orders products
• Ideally humans would visit all, or all major
  online stores but too time consuming
• Web agents such as Shopbots are proposed to
  automate the process.

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Technical difficulties with todays web

• Searching information
• Keyword-based search engines
• Extracting information
• Human involvement necessary for browsing,
  retrieving, interpreting, combining
• Maintaining information
• Inconsistencies in terminology
• Outdated information.
• E.g., A person can not teach and take a course
  at the same time
• Integrating information

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Key problem in todays web

• The meaning of Web content is not
  machine-accessible lack of semantics
• It is simply difficult to distinguish the meaning
  between these two sentences
• I am a professor of computer science.
• I am a professor of computer science, you may
  think. Well, . . .

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The semantic web approach

• Represent web content in a form that is more
  easily machine-processable.
• Use intelligent techniques to take advantage of
  these representations.
• The Semantic Web will gradually evolve out of the
  existing Web, it is not a competition to the
  current WWW.

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Semantic web technologies

• Explicit Metadata
• Ontologies
• Logic and Inference
• Web service
• Data integration
• Intelligent software agents

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HTML

• lth1gt Agilitas Physiotherapy Centre lt/h1gt
• Welcome to the home page of the Agilitas
  Physiotherapy Centre. Do
• you feel pain? Have you had an injury? Let our
  staff Lisa Davenport,
• Kelly Townsend (our lovely secretary) and Steve
  Matthews take care
• of your body and soul.
• lth2gt Consultation hours lt/h2gt
• Mon 11am - 7pm ltbrgt
• Tue 11am - 7pm ltbrgt
• Wed 3pm - 7pm ltbrgt
• Thu 11am - 7pm ltbrgt
• Fri 11am - 3pm ltpgt
• But note that we do not offer consultation during
  the weeks of the
• lta href". . ."gtState Of Origin lt/agt games.
• Markups are for formatting or presentation
• Web contents are for humans instead of programs

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Problems with HTML

• Humans have no problem with this.
• Machines (software agents) do.
• How distinguish therapists from the secretary
• How determine exact consultation hours
• They would have to follow the link to the State
  Of Origin games to find when they take place.

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A better representation

• ltcompanygt
• lttreatmentOfferedgtPhysiotherapylt/treatmentOffered
  gt
• ltcompanyNamegtAgilitas Physiotherapy Centre
  lt/companyNamegt
• ltstaffgt
• lttherapistgtLisa Davenportlt/therapistgt
• lttherapistgtSteve Matthewslt/therapistgt
• ltsecretarygtKelly Townsendlt/secretarygt
• lt/staffgt
• lt/companygt

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Explicit Metadata

• This representation is far more easily
  processable by machines
• Metadata data about data
• Metadata capture part of the meaning of data
• Semantic Web does not rely on text-based
  manipulation, but rather on machine-processable
  metadata
• Meta data is not enough

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Ontology

• Long history coming from Philosophy, introduced
  by Aristotle's
• An ontology is a formal, explicit specification
  of a shared conceptualization
• -- Gruber

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Web Ontology Languages

• RDF Schema
• RDF is a data model for objects and relations
  between them
• RDF Schema is a vocabulary description language
• Describes properties and classes of RDF
  resources
• Provides semantics for generalization hierarchies
  of properties and classes.
• OWL
• A richer ontology language
• More relations between classes
• e.g., disjointness
• Cardinality
• e.g. exactly one
• Richer typing of properties
• Characteristics of properties (e.g., symmetry)

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Tradeoff between Expressive Power and
Computational Complexity

• The more expressive a logic is, the more
  computationally expensive it becomes to the
  inferences
• Drawing certain conclusions may become impossible
  if non-computability barriers are encountered.

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Software agent

• Software agents work autonomously and proactively
  
• They evolved out of object oriented and
  component-based programming
• For example, a personal agent on the Semantic Web
  will
• receive some tasks and preferences from the
  person
• seek information from web sources, communicate
  with other agent
• compare information about user requirements and
  preferences, make certain choices
• give answers to the user

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Agent technologies

• Further technologies (orthogonal to ontology)
• Agent communication languages
• Formal representation of beliefs, desires, and
  intentions of agents
• Creation and maintenance of user models.

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The semantic web layer cake

• The development of the Semantic Web proceeds in
  steps
• Each step building a layer on top of another
• Principles
• Downward compatibility
• Upward partial understanding

OWL
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Semantic Web Layers

• XML layer
• Syntactic basis
• RDF layer
• RDF basic data model for facts
• RDF Schema simple ontology language
• Ontology layer
• More expressive languages than RDF Schema
• Current Web standard OWL
• Logic layer
• Enhance ontology languages further
• Application-specific declarative knowledge
• Proof layer
• Proof generation, exchange, validation
• Trust layer
• Digital signatures
• Recommendations, rating agencies .

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The semantic web wave
OWL-S
HTML
Latex
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Semantic Web and Web Service (SW WS)
SWS, Intelligent Web Agent
Semantic Web (RDF, RDFS, OWL, )
Web Service (WSDL, SOAP, UDDI, )
WWW (HTML, HTTP, URI, )