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WWW was born at European Nuclear Research Center, CERN 1990
Authors
JCR Licjlider
Robert Taylor
Larry Roberts
02 Limits of the current web
WEb is supposed to be used by humans
HTML describes
how information is presented
how information is linked
but not what information means
03 Importance of Meaning
Semantic
Pertains to the character, the study of meaning.
It is the study of interpretations of signs or symbols as used by agents or communitites.
The semantics of a message depends on context and pragmatics.
Syntax
Arragngement, ordering as in grammatics denotes the study of principles and processes by which sentences are constructed in a particular language.
Context
denotes the surrounding of a symbol in an expression.
It is neccessary to make sense of the semantics, to determine the meaning.
-Pragmatics
reflects the intention by which the language is used to comminicate a message. It also denotes the intended purpose of the speaker.
Successful Communication
information has to be correctly transmittted (Syntax)
meaning (Semantics) of information must be intepreted correctly
understanding depends on the
context of both sender and receiver
pragmatics of the sender
contest of sender and receiver depends on the
experience of the sender and receiver
04 The limits of the web
Problem 1: Information Retrieval
traditional keyword-based search does not fild all results
synonyms and metaphors
Polusemy - missing context definition
Problem 2: Information Extraction
can only be solved correctly bu a human agent
heterogeneous distribiution and order of information
Problem 3: Maintanance
syntatic and semantic consitency
correctness
timeliness
Personalization
adaptaion of the presented information content to personal requirements
Data is locked in small data islands.
Other applications usually cannot access this data
Apply semantiv technologies with RDF and OWL to link data between the islands.
linked Data Principles
Use URI's as names for things
Use HTTP URI's so that people can look up those names
For each URI, provide useful information using the standards (RDF, SPARQL)
Include links to related URI's and other objects.
Explanation
Use HTTP URI's so that people can look up those names
Use http content negotiation to differentiate resource for machine/humans
-- application/rdf+xml or application/text+html
For each URI, provide useful information using the standards (RDF, SPARQL)
make all rui in the rdf graph deferencable.
avoid rdf constructs that cause problem in linked data context
-- rdf reification
-- rdf collections and containers
-- unnamed blank nodes - because they are not accessible from outside.
Include links to related URI's and other objects.
relationship links
identity links
vocabulary links
Semantic Maships
Are applications that use linked RDF data from varous data sources.
enables navigation
helps crawlers
Linked data engineering 2
OWL
owl:same as -> connect identical indiciduals
owl:equivalentClass -> connect equivalent class
It cannot connect almost similar classes -: limitation
Unbel Ontologies
Upper Mapping and Binding Exchange Layer
Subset of OpenCyc
as RDF Tribles based on SKOS and OWL2
Upper ontology with 28,000 ontologies
SKOS
Simple Knowledge Organization System
bsed on RDF and RDFS
Concept, Symbol and Object
Concept symbolizes Symbol which stands for an object. Concept refers to object.
URI - Uniform Resource Identifier defines a simple and extensible schema for worldwide unique identification of abstract or phisycal resources.
Designator, Designatum
Designatiror showcases and discusses the real world object - designatum.
A resource can be described (designated) via Metadata
Resouce representation might be available that describes the resource sufficiently from the web server.
URI
URI combines
Address (Locator)
URL
might change during life cycle
Identity (Name)
URN
persistant identifyer for web resouce
remains unchanged during life cycle
Seperate URI for designator and designatum
02 How to Represent Facts
Resource Description Framework
Intuitive knowledge representation with directed graphs
Level 1 (objects) : XML
Level 2 (knowledge about objects): RDF and RDFSchema
Level 3 (entire world): OWL and Rules (web ontology language)
RDF
Resource
can be anything
must be uniqly identifiable
Description
desc of resouces
via representation properties and relationships among resouces
relattionships can be representated as graphs
Framework
made of web frameworks
based on formal semantic models
knowledge in rdf is expressed as a list of statements
Subject -> Property -> object
RDF-TRIPLE:
Resouce + Property + Object/Value
Constituents of RDF graphen
URI / Another Resource
LITERALS
BLANK NODES
RDF representations
NodeEdge - NodeTriple
N3 Notation
{ SUBJECT_URI,
SUBJECT_URL#Property,
OBJECT_URI
}
Turtle (Turse RDF Triple Language)
<subject><property><object> . <= for uri
<subject><property>"object" . <= for literals
or can use prefix
@prefix mail: <sayoojsamuel@gmail.com>
We also have RDF xml serializarion to make it compatable with xml framework
03 | How to Represent facts Part 2
RDF with xml example
<xmlversion="1.0"encodin="utf-8">
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns# "
xmlns:pers="http://hpi-web.de/Personal#"
xml:base="http://hpi-web.de/Lecturer">
<rdf:Descriptionrdf:about="#HaraldSack" // rdf:ID="HaraldSack" is an alternative without #
pers:hasPhoneNumber="++123456789">
<pers:writesBlogrdf:resource="http://block.com"/>
</rdf:Description>
<rdf:RDF>