Semantic Web Presentation

schoolmistInternet and Web Development

Oct 22, 2013 (4 years and 18 days ago)

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The W3C’s Semantic Web




Kyle Mosack

The Semantic Web


"The Semantic Web is not a separate Web
but an extension of the current one, in
which information is given well
-
defined
meaning, better enabling computers and
people to work in cooperation." It is a
source to retrieve information from the web
(using the web spiders from RDF files) and
access the data through Semantic Web
Agents or Semantic Web Services.”


Source: "The Semantic Web" by Tim Berners
-
Lee, James Hendler, and Ora Lassila, Scientific
American, 2001

What It Could Be


Machine Readable Data View


Having data on web be defined an linked in a way that
can be read by machine for automation, integration,
and re
-
use across different applications


Intelligent Agent View


Agents retrieve and manipulate pertinent information


Distributed Data View


Provide sufficient flexibility to be able to represent all
databases and logic rules to link them together


Automated Infrastructure View


Current web lacks an easy automation framework

What it Could Be


Servant of Humanity View


Enable Web applications to automatically collect ,
integrate, and process information and interoperate
with other applications


Better Annotation View


Annotations expressed in a machine
processable

form
and linked together


Improved Searching View


Access Web content by concepts instead of keywords


Web Services View


Expand services from existing web by automating
services with Web agents


Semantic Web Layer Cake


Semantic Web Layer Cake


Readable Description Framework


Designed for specific data about specific
subjects


Can represent Data and Metadata


Moves proprietary data to a form
computers can analyze


Recommendation from W3C for
Semantic Web

RDF



To be successful RDF must be able to



Describe most kinds of data that will be
available



Describe structural design of data sets



Describe relationships between bits of data

RDF


Creates a data model with triplets


Subject, predicate (property), object (property
value)


These are statements about resources


Identified by URI


Easily convertible


Not limited by predefined database values


Flexible

RDF Graph with Anonymous Nodes


RDF Applications


Mozilla


Uses XUL (extensible user interface language)


Uses RDF as a source for listings and other control
information that defines which XUL files to use for
specific XUL interfaces


RSS (Really Simple Syndication)


Helps spread summaries of personal blogs cheaply and
easily


Uses
RDF’s

XML exchange format


One of the few RDF applications that is distributed
over the Web rather than being used locally, unlike
Mozilla application


Can be seen as an early, maybe primitive, Semantic Web Application

RDF Applications


RDF for annotations:
Annotea


Experimental scheme by W3C for annotating
Web pages


Bibliographic meta data: Dublin Core


Provides practical standard terms applicable to
nearly any published work


Webscripter
: Fusing Information


DAML (DARPA Agent Markup Language)


Ability to make up web pages so that information
about the page can be extracted in a uniform way
and combined with other web pages

RDF and the Semantic Web


Abilities beyond conventional database


Combine data with different data sets that don’t follow
the same data models


Add data that doesn’t fit the table structures


Exchange data with any other application that can
handle RDF


Use an RDF processor that can do logical reasoning to
discover unstated relationships


Use someone else’s ontology to learn more about own
data


Add statements about publications and references that
have been defined somewhere else on the Web


Do all these things using well defined standards, so
wide range of applications can process the data

RDF


Potential Problems



Many stem from nature of the Web


Incomplete information


Contradictory or unreliable information


Full first order logic requires an ability to
generate general statements about the
whole table


No way to negate statements


May not be powerful enough

Ontology


Study of existence or being


The kinds of things that can be talked
about in a system or context


Provides the means to classify these
properties


Name and label them


Kinds of organization include


Lists, hierarchies, and trees

Ontology


The ontology of a complicated semantic
system can capture enough knowledge so
a computer can perform everyday
knowledge


To define a set of classes that together cover
a domain of interest


Framework provides syntax, vocabulary,
and some pre
-
defined terms


Framework is an ontology for constructing
ontology


Ontology Considerations


Merging Ontology


Terms and classes can by understood by more
than one ontology


Can be accomplished by using same system
(like OWL)


Even if able to merge, inconsistencies could
jeopardize reliability


Imports of second ontology should be kept
simple and be done so in small sections

Merging Ontology

Ontology Considerations


Problems with importing a large
Ontology


Vocabulary may change over time once
ontology is developed


Already committed to the vocabulary that is
distributed


Can be limited by designer but no solutions
have been made available

Ontology Languages


Frameworks with Web
-
like uses


RDFS



Resource Description Framework Schema
Specification


Base RDF language for describing ontology


Built on top of RDF


RDF makes statements about resources, making assertions
about a subject


Every RDFS statement is a legal RDF Statement


RDF classes and properties


Together with standard classes, possible to give basic
characteristics of classes for an ontology


Not enough power to express many constraints or logical
properties

Ontology Languages


OWL (Web Ontology Language)


Final Recommendation by W3C


Built to standardize a more capable Ontology
Framework than RDFS



Need to restrict Cardinality


Express optionally


Combine classes



Ontology Summary


To be useful for the semantic Web, an ontology
l
anguage must be:


Able to reference concepts defined elsewhere on
Web


Sharable over the Web


Be able to work with one or more languages


Able to merge several different
ontologies


Widely accepted as a standard


Expressive enough for serious use


Support logical functions that are needed to conduct
business of the semantic Web


Last two points are questioned abilities of OWL

Logic


Uses in the Semantic Web


Applying and evaluating rules


Inferring facts that haven’t been explicitly stated


Explaining why a particular conclusion has been reached


Detecting contradictory statements and claims


Specifying ontology and vocabulary of all kinds


Representing knowledge


Describing the kinds of things that may be said about a subject


How those statements are to be understood


The statement and execution of queries to obtain
information from stores of data


Combining information from distributed sources in a
coherent way

Logic


There is considerable risk that an
open

system

will absorb contradictory or
incorrect information


Most reasoning systems can not capture
explanations


Ones that are able to can not do so in a uniform,
easy to read way


More current versions of RDF define ways
to understand a collection of RDF
statements that can deal with the possibility
of contradictory information


Requires more computing power

Logic


Logic and Ontology


Ontology defines concepts and terms


Logic provides ways to make statements that
define the use of concepts and terms


To reason about collections of statements that use
the concepts and terms

Logic


Logic and Representing Knowledge


Logic is a formal discipline dealing mostly with
formal language that can express a subset of
everything that can be articulated using
natural language


Formal description of data and information
naturally involves the use of logic

Logic


Queries


Logical descriptions of information to be
retrieved from a database


Queries will need to operate across
distributed sources of data to be effective in
the Semantic Web


Needs to reconcile the differences in ontology and
deal with problems of contradictory data

Logic


Problems of Semantic Web logic looks to
deal with


When trying to decide what data should be
imported from remote database


Size of the knowledge base might be too large and
overwhelm resources


Importing data without duplicating knowledge


How much is interconnected?


Don’t want to import automatically because of a
formation of any new data


Importing unreliable information


Contaminate good data

Trust


With development in utility of Web, trust
needs to be established between system
and user


Trust


Identity: Who are you?


Why should I trust you?


Who else trusts you?


How much should I trust you?


How do I know that you said what you
claimed you have said?

Trust


Belief


How much confidence should I place in what
you say?


What should I believe when different facts
don’t agree


How much should my prior beliefs influence
my confidence in what you say?


How can I establish the correct degree of
belief for a given set of information?

Tools of Trust


Keys


Private and Public


Digests


Special summary of a document or message
that can not be reversed to the original, no
key needed


Slight differences in messages amount to large
differences in digest


Similarity of digests can not be used to
predict similarity in messages

Tools of Trust


Public Key Infrastructure (PKI)


Widespread system


Certificate Authority (CA) issues digital certificate


CA trustworthy source


CA signs certificate for other
CAs


Creates chain of certifications, eventually amounting
to a size that alleviates issues of trust


Potential problems


If CA private key compromised, entire chain untrustworthy


Large cross
-
certified chains can become unmanageable


CAs

may have different standards


Human error and fraud


Digital Signatures


Authenticated by CA or CA chain

Video





The Semantic Web


Work Cited

Passin
, T. B.
Explorer's guide to the semantic web
. Manning Publications,
2004. Print.


http://www.w3schools.com/web/web_semantic.asp


http://www.semanticfocus.com/media/insets/semantic
-
web
-
layer


cake
-
2.pnghttp://www.xml.com/2003/02/05/graphics/graph1.gif


http://www.codeproject.com/KB/books/GuideSemanticWeb/img002.jp
g


http://
searchsoa.techtarget.com
/definition/Semantic
-
Web


http://
semanticweb.org/wiki/Semantic_Web