lecture 1: introduction
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the semantic web vision
today’s web (1)
web content – for human consumption
(no structural information)
people search for information, keep in touch with
other people, make purchases, look for
entertainment … minimal support by software tools
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the semantic web vision
today’s web (2)
keyword-based search engines … with some
problems:
 high recall & low precision – too many documents retrieved
 low/no recall – no relevant documents found
 results sensitive to vocabulary – similar words not considered
 results are single web pages – “distributed” information not
retrieved
 human needed for interpretation, no other software tools use the
result
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the semantic web vision
today’s web (3)
a problem with semantics …
so
… a need for different representation of information,
and intelligence that takes advantage of that
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the semantic web vision
… the future (1)
knowledge management
 key activity of large businesses (knowledge seen
as intellectual asset)
 information is in a weakly structured form
 problems with: sharing, extracting, marinating,
viewing
Semantic Web -> knowledge organized, tools for
knowledge maintenance, query answering tools
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the semantic web vision
… the future (2)
business-to-customer electronic commerce
 browsing on-line shops, selecting the best
alternative/offer -> time and effort consuming
activity
 decisions making based on limited/partial
information
Semantic Web -> software “shopping” agents able to
interpret the product information and the terms of
service, and conduct negotiations
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the semantic web vision
… the future (3)
business-to-business electronic commerce
 data exchange using the Electronic Data Interchange
(EDI) approach (complex, isolated)
 lack of standards
Semantic Web -> differences in terminology resolved
(abstract domain models), automatic translation of
services, auctioning, negotiations, and drafting of
contracts
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the semantic web vision
… the future (4)
wikis
 collections of pages that allow users to add content
(collaborative knowledge creation)
Semantic Web -> usage of semantic technologies
(enriching structured text and untyped hyperlinks with
semantic annotation referring to an underlying model
of the captured knowledge)
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the semantic web vision
… the future (5)
personal agents: a future scenario
Michael has some neck pain, he asked his
Semantic Web agent to arrange for him physical
therapy sessions which were suggested by
Michael’s physician …
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semantic web technologies
metadata (1)
HTML is the predominant language used for writing web
pages
humans have no problem reading it
machines are not able to distinguish different people, things,
follow links to find out more about topics – simple they have
no clue what a given text is about
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semantic web technologies
metadata (2)
<company>
<companyName>… </companyName>
<staff>
<director> … </director>
<viceDirector> … </viceDirector>
</staff>
</company>
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semantic web technologies
metadata (3)
HTML is replaced by a language that carries information
about a content
metadata – data about data, capture part of the
meaning of data (tags that are “defined” in a
systematic way)
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semantic web technologies
ontology (1)
study of nature of existence, how to describe things
that actually exist
world is made up of specific objects that can be
grouped into abstract classes based on shared
properties
it describes a domain of interest
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semantic web technologies
ontology (2)
consists of a finite list of terms and the relationships
between them
terms denote concepts (classes of objects) of the
domain
relationships include hierarchies of classes
+ properties of objects, value restrictions, logical
relationships between objects
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semantic web technologies
ontology (3)
provide “a shared understanding of a domain”
overcome differences in terminology
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semantic web technologies
ontology languages
RDF – is a data model for objects and relations between
them
RDF Schema – a description language for describing
properties and classes of RDF resources, provides a
semantics for generalization hierarchies
OWL – a rich language for describing properties and
classes, and relations between them
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semantic web versus AI
logic (1)
provides principles of reasoning
provides well-understood formal semantics
“unlocks” automated reasoners
leads to uncovering ontological knowledge given
implicitly
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semantic web versus AI
logic (2)
used by intelligent agents for making decisions and
selecting courses of action
provides explanations for conclusions
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semantic web versus AI
logic (3)
SWRL – semantic web rule language for constructing
rules based on ontology classes and relationships
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semantic web versus AI
agents (1)
software agents work autonomously and proactively
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semantic web versus AI
agents (2)
tasks of personal software agent in SW:
 receive tasks and preferences from users
 seek information on the web, communicate with other
agents
 compare information from different sources, make choices
 give answer to users
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semantic web versus AI
agents (3)
metadata
 identify and extract information
ontology
 web search, information interpretation
 communication with other agents
logic
 information retrieval, conclusion derivation
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a layered approach
development of SW in steps
each step building a layer on the top of another
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a layered approach
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a layered approach
alternative stack
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a layered approach
XML layer
 syntactic basis
RDF layer
 basic data model for facts
 RDF Schema simple ontology language
ontology layer
 more expressive languages - OWL
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a layered approach
logic layer
 enhance ontology, application specific knowledge
proof layer
 proof generation, validation
trust layer
 digital signature, rating agents …
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the semantic web vision
… the present (1)
linked data
a new paradigm built on one of the layers of SW –
RDF core
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the semantic web vision
… the present (2)
linked data
each piece of information is linked to other pieces
different types of links
different sources of data
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the semantic web vision
… the present (3)
linked data
every piece of information presented as a triple:
subject-property-object
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the semantic web vision
… the present (4)
linked data
a vast, interconnected web of triples (pieces of
information)
easy to query with SPARQL – a special query
language for RDF
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the semantic web vision
…
linked data
linked data
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future web …
intelligent representation
and processing of data
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