Semantic Web

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22 Οκτ 2013 (πριν από 3 χρόνια και 7 μήνες)

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JOSH FLECK

Semantic Web

What is Semantic Web?


Movement led by W3C that promotes common
formats for data on the web


Describes things in a way that computer applications
can understand it


Describes the relationship between things and
properties of things


Tries to organize and structure the current Web’s
documents into a logical group or web of data

What is Semantic Web?


"If HTML and the Web made all the online
documents look like one huge book, RDF, schema,
and inference languages will make all the data in the
world look like one huge database“
-

Tim Berners
-
Lee, Weaving the Web, 1999


Uses Linked Data


Semantic Web Stack

Linked Data


Uses the Web to create links between data from
different sources


Refers to data published on the Web in way that is
machine
-
readable, its meaning is explicitly defined,
it is linked to other external data sets, and it can be
linked to from external data sets


Allows applications to grab large amounts of related
data


Is created by using URIs and RDF

Uniform Resource Identifier (URI)


String of characters that represents a resource


Used as an identifier so that interactions can take
place


Can be classified as a locator (URL), name (URN), or
both


Name provides a resource’s identity and locator
provides an address


URN example: “
XMLSchema



URL example:
http://www.w3.org/2001/XMLSchema

Resource Definition Framework (RDF)


Standard built on top of XML to describe
information about resources on the Web


Intended for representing metadata about Web
resources ex: title, author, data of a Web page


Intended to be used by applications rather than
being seen by users


Puts information of a resource into triple expressions

Triple Expressions


Extensible Markup Language (XML)


Used to encode the RDF


Two types of XML nodes in a RDF/XML document


Resource Nodes


Property Nodes

RDF Schema (RDFS)


Set of classes with certain properties using RDF


Provides basic elements for the description of
ontologies
, used to structure RDF resources


These resources can be saved in a triple to reach
them with the query language SPARQL

Core Components of RDFS Classes


rdfs:Resource
: All things described by RDF are called
resources, and are instances of the class
rdfs:Resource


rdfs:Class
: This is class of resources that are RDF
classes


rdfs:Literal
: The class of literal values such as strings
and integers


rdfs:Datatype
: The class of data
-
types


rdf:XMLLiteral
: The class of XML literal values


rdf:Property
: The class of RDF Properties


Core Components of RDFS Properties


rdfs:range
: Used to declare the class or data
-
type of the
object in a triple


rdfs:domain
: Used to declare the class of the subject in a
triple


rdfs:type
: Used to state that a resource is an instance of a
class


rdfs:subClassOf
: Used to state that all resources related
by one property are also related by another


rdfs:label
: Used to provide a human
-
readable version of
a resource’s name


rdfs:comment
: Used to provide a human
-
readable
description of a resource


Ontology


Also known as RDF vocabularies


Defines the terms, data, and relationships of data


Most common standard is Web Ontology Language
(OWL)

Components of Ontology


Individuals: instances or objects (the basic or "ground
level" objects)


Classes: sets, collections, concepts, classes in
programming, types of objects, or kinds of things


Attributes: aspects, properties, features, characteristics,
or parameters that objects (and classes) can have


Relations: ways in which classes and individuals can be
related to one another


Function terms: complex structures formed from certain
relations that can be used in place of an individual term
in a statement


Components of Ontology


Restrictions: formally stated descriptions of what
must be true in order for some assertion to be
accepted as input


Rules: statements in the form of an if
-
then
(antecedent
-
consequent) sentence that describe the
logical inferences that can be drawn from an
assertion in a particular form


Components of Ontology


Axioms: assertions (including rules) in a logical form
that together comprise the overall theory that the
ontology describes in its domain of application


Events: the changing of attributes or relations


SPARQL


Able to retrieve and manipulate data stored in RDF


Allows for a query to consist of triple patterns,
conjunctions, disjunctions, and optional patterns


Implementations for multiple programming
languages exist

SPARQL Queries


SELECT Query: results are returned in a table format


CONSTRUCT Query: results are returned in RDF
form


ASK Query: results are either True or False


DESCRIBE Query: returns a RDF graph containing
RDF data about resources

SPARQL

Rule Interchange Format


Originally envisioned as a rules layer for the
semantic web


Instead, it recognizes that there are many rule
languages and what is needed to exchange rules
between them

Future of the Web


Gives information on the Web meaning


Gathers information from different sources


Rather than just having the details together on the
screen, they will have a relationship in the code

Challenges


Vastness


Vagueness


Uncertainty


Inconsistency


Deceit

Disadvantages of Semantic Web


The Web currently uses HTML while Semantic Web
uses RDF


Semantic web is mostly unknown and there are few
people that know how to write a web page in RDF


Censorship


Doubling output formats

Examples of Semantic Web


DBpedia


FOAF


Digital music archives


SAPPHIRE


Relfinder

DBpedia


Allows users to find answers to questions that are
spread across many different Wikipedia pages


http://wiki.dbpedia.org/FacetedSearch?v=pjv

Friend of a Friend (FOAF)


Uses RDF to describe the relationships people have
to other people and things around them


Lets intelligent agents make sense of the thousand of
connections people have with each other, their jobs,
and items important to their lives


Example of how Semantic Web attempts to make use
of the relationships in a social context

Digital Music Archive


Digitize the huge music material at the Norwegian
National Broadcaster (NRK)


Use the repository asset in new productions, with
better search and access


Semantic Web is used to manage the huge amount
of metadata, and provide easy and quick access to
the asset




SAPPHIRE


An integrated
biosurveillance

system; integrates data
from multiple sources


Data can be viewed from many different perspectives
(disease surveillance, environmental protection,
biosecurity

and bioterrorism, veterinary surveillance,
etc.)


SAPPHIRE receives reports every 10 minutes on
emergency room cases, patients’ symptoms, health
records, and clinicians’ notes from other hospitals in
the area



RelFinder


http://www.visualdataweb.org/relfinder/relfinder.p
hp

Conclusion


Web of Data


Stores meaning

Questions?


References


Christian
Bizer
, T. H.
-
L. (2009).
Linked Data
-

The Story So Far.

Retrieved
March 25, 2012, from Tom Heath: http://tomheath.com/papers/bizer
-
heath
-
berners
-
lee
-
ijswis
-
linked
-
data.pdf


Lee
Feigenbaum
, I. H. (2009, January 19).
The Semantic Web in Action
.
Retrieved March 25, 2012, from Scientific American:
http://people.cs.kuleuven.be/~danny.deschreye/SemanticWebAction.pdf


Mirhaji
, P. (2007, March).
Semantic Web Use Cases and Case Studies
.
Retrieved March 25, 2012, from W3C:
www.w3.org/2001/sw/sweo/public/UseCases/UniTexas


Ontology (information science)
-

Wikipedia, the free encyclopedia
. (
n.d
.).
Retrieved April 15, 2012, from Wikipedia, the free encyclopedia:
en.wikipedia.org/wiki/Ontology_(
information_science
)


RDF Schema
. (
n.d
.). Retrieved April 15, 2012, from W3C:
www.w3.org/TR/rdf
-
schema/#ch_properties


Semantic Web
. (
n.d
.). Retrieved March 25, 2012, from W3C:
http://www.w3.org/standards/semanticweb/

References


Semantic Web
-

Wikipedia, the free encyclopedia
. (2012). Retrieved
March 2012, 8, from Wikipedia, the free encyclopedia:
http://en.wikipedia.org/wiki/Semantic_Web


SPARQL Query Language for RDF
. (2008, January 15). Retrieved
March 25, 2012, from W3C: http://www.w3.org/TR/rdf
-
sparql
-
query/


Tauberer
, J. (2008, January).
What is RDF and what is it good for?

Retrieved March 25, 2012, from Resource Description Framework:
http://www.rdfabout.com/intro/


The Semantic Web
. (
n.d
.). Retrieved March 25, 2012, from
w3schools.com: www.w3schools.com/web/web_semantic.asp


Tønnesen
, D. R. (2007, September).
Case Study: A Digital Music
Archive (DMA) for the Norwegian National Broadcaster (NRK)
using Semantic Web techniques
. Retrieved March 25, 2012, from
W3C: http://www.w3.org/2001/sw/sweo/public/UseCases/NRK/