Transcript Semantic Web - ????????
Semantic Web
Dr. Mohsen Kahani [email protected]
http://web.um.ac.ir/~kahani/
SW Scenario
“At the doctor's office, Lucy instructed her Semantic Web agent through her handheld Web browser. The agent promptly retrieved information about Mom's prescribed treatment from the doctor's agent, looked up several lists of providers , and checked for the ones insurance within a 20- mile radius in-plan for Mom's of her home and with a rating of excellent or very good on trusted rating services. It then began trying to find a match between available appointment times (supplied by the agents of individual providers through their Web sites) and Pete's and Lucy's busy schedules.” (The emphasized keywords indicate terms whose semantics, or meaning, were defined for the agent through the Semantic Web.) Scientific American: The Semantic Web: May 2001 < http://www.sciam.com/2001/0501issue/0501berners-lee.html>
Doctor’s appointment
“The Semantic Web”,
Scientific American, May 2001 Insurance Co.
Rating Provider sites Mom Physician’s Agent
required treatment in-plan?
close-by?
Specialist?
Schedule appointment Driving schedule
Lucy’s Agent Pete’ Agent
“Most of the Web's content today is designed for humans to read, not for computer programs to manipulate meaningfully.”
Berners Lee, T, Hendler, J & Lassila, O ‘The semantic web’,
Scientific American
, May 2001
Where we are Today: the Syntactic Web
Current Web
500 million user more than 8 billion pages
Static
WWW
URI, HTML, HTTP
The vision
The World Wide Web is a big and impressive success story, both in terms of the amount of available information and the growth rate of human users It starts to penetrate most areas of our daily life and business.
This success is based on its simplicity the restrictivenss of HTTP and HTML allowed software developers, information providers and users to make easy access of the new media helping it to reach a critical mass
The Vision
However this simplicity may hamper the further development of the Web What we see currently is the very first version of the web and the next version will probably even more bigger and much powerful compared to what we have now.
Semantic Web
Serious Problems in information
•
finding
•
extracting
•
representing
•
interpreting
•
and maintaining
Static
WWW
URI, HTML, HTTP
Semantic Web
RDF, RDF(S), OWL
Semantic Web Technology
Tim Berners-Lee has a vision of a Semantic Web which
has machine-understandable semantics of information, and
millions of small specialized reasoning services that provide support in automated task achievement based on the accessible information
The Syntactic Web is…
A hypermedia, a digital library
A library of documents called (web pages) interconnected by a hypermedia of links
A database, an application platform
A common portal to applications accessible through web pages, and presenting their results as web pages
A platform for multimedia
BBC Radio 4 anywhere in the world! Terminator 3 trailers !
A naming scheme
Unique identity for those documents
A place where computers do the presentation (easy) and people do the linking and interpreting (hard). Why not get computers to do more of the hard work?
What is the Problem?
Markup consists of: rendering information (e.g., font size and colour) Hyper-links to related content Semantic content is accessible to humans but not (easily) to computers…
What information can we see…
WWW2002 The eleventh international world wide web conference Sheraton waikiki hotel Honolulu, hawaii, USA 7-11 may 2002 1 location 5 days learn interact Registered participants coming from australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire Register now On the 7 th May Honolulu will provide the backdrop of the eleventh international world wide web conference. This prestigious event … Speakers confirmed Tim berners-lee Tim is the well known inventor of the Web, … Ian Foster Ian is the pioneer of the Grid, the next generation internet …
What information can a machine see…
WWW2002 The eleventh international world wide web conference Sheraton waikiki hotel Honolulu, hawaii, USA 7-11 may 2002 1 location 5 days learn interact Registered participants coming from australia, canada, chile denmark, france, germany, ghana, hong kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire Register now On the 7 th May Honolulu will provide the backdrop of the eleventh international world wide web conference This prestigious event Speakers confirmed Tim berners-lee Tim is the well known inventor of the Web, Ian Foster Ian is the pioneer of the Grid, the next generation internet
Solution: XML markup with “meaningful” tags?
That is, structure and semantics of documents are interwoven
Agree upon the meaning of tags through the use of namespaces
XML Is Not Enough!
XML: Should be used Is extensible (DC qualifiers)
mean
?) The meaning may be agreed & understood within DC applications – but this does not allow for
extensibility
Similar applications may be described using different XML DTDs: e.g. is
Scenario – Buying A Car
User
You live in London and want to buy a car locally. You can afford up to £500. The car must be red.
Honest EuroJoe’s Used Car Web Site
Joe uses:
Result
• Car not found – even though structured information is provided. • A human would know that this was a valid match, because it understands the meanings and relationships.
• The Semantic Web aims to solve this problem.
We Need Extensibility!
We can see a progression from Web sites which are: •
Joe’s Used Cars
Ford Escort
This maroon car costs €400
Buying Car On The Semantic Web
Motor Trade schema database model Scottish Motor Trade schema Mapping service Joe’s Used Car Web Site Ford dealers schema vehicle-type Wordnet Joe is part of the motor trade association, which has defined its own schema for selling cars.
The Scots use a different schema, as do the car manufacturers (which mainly sell new cars).
A mapping service provides a mapping between these machine understandable schemata.
Wordnet maps relationships between words (e.g. red and maroon)
The Semantic Web
A Vision Of Possibilities
“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 and Ora Lassila, The Semantic Web, Scientific American, May 2001
Scenario – Buying A Car (2)
We’ve seen how this query can be answered:
Find me a red car in London for < £500.
How about this maroon Escort in Brixton for €400?
The Semantic Web will be extensible enabling interactions with other services which may use different XML DTDs:
Give me the AA’s report on this type of car.
OK here it is
Check the DVLA details for the reg. no.
OK – the car is registered correctly
Model For Buying A Car
Motor Trade schema database Scottish Motor Trade schema Ford dealers schema AA Web site Mapping service AA vehicle schema Joe’s Used Car Web Site Value-added services DVLA schema With machine-understandable data it becomes easier to extend services
Need to Add “Semantics”
External agreement on meaning of annotations
E.g
.,
Dublin Core
• • • • • Agree on the meaning of a set of annotation tags
Title
: A name given to the resource.
Creator
: An entity primarily responsible for making the
Subject
: The topic of the content of the resource.
Description
: An account of the content of the resource . ….
Problems with this approach
• Inflexible • Limited number of things can be expressed
Need to Add “Semantics” (Cont.)
Motivation toward RDF(S), DAML+OIL, OWL,…
Establish a widely accepted standard for representing expressive declarative knowledge on the Web.
Knowledge Representation Knowledge sharing Communication Language for query
Representation Language (RL)
Representation means that we encode the description in a way that enables someone to use it
Some representational languages are:
- UML - RDF(S) - Topic Maps - DAML+OIL - OWL …..
Levels of Representation Needed for Models
Syntax
- An XML document is syntactically correct or not
Structure
Validating an XML document with respect to DTD or XML Schema language
Semantic
- Mapping between some structured subset of data and a model of some set of objects in the domain
Pragmatics
- Has to do with the intent of the semantics and actual semantic usage
• • •
RDF (
Resource Description Framework
)
RDF provides a way of describing resources via metadata (data about data) It restricts the description of resources to
triplets (subject,predicate,object)
It provides interoperability between applications that exchange machine understandable information on the Web.
The original broad goal of RDF was to define a mechanism for describing resources that makes no assumptions about a particular application domain, nor defines (a priori) the semantics of any application domain. • • Uses XML as the interchange syntax. Provides a
lightweight
ontology system.
The formal specification of RDF is available at: http://www.w3.org/TR/REC-rdf-syntax/
RDF (cont
’
d)
An example of RDF using the Dublin Core language
RDF Syntax
Subject, Predicate and Object Triplets (Tuples) • Subject: The resource being described.
• Predicate: A property of the resource • Object: The value of the property A combination of them is said to be a Statement (or a rule) John Doe http://foo.bar.org/index.html
A web page being described Author A property of the web page (author) [Subject] [Predicate] The value of the predicate (here the author) [Object]
RDF Example
is “John Doe” In this way, we can have different objects (resources) pointing to other objects (resources) You can also make statements about statements – reification Ex: ‘xyz’ says that ‘ The Author of http://foo.bar.org/index.html
is John Doe’
RDF Schema
• A schema defines the terms that will be used in the RDF statements and gives specific meanings to them.
http://www.w3.org/TR/rdf-schema/
Example:
subclass
of MotorVehicle
Example (cont..)
Multiple Inheritance
Domain
of a property
Range
of a property
Ontology
Ontology
is a term borrowed from philosophy that refers to the science of describing the kinds of entities in the world and how they are related An
OWL ontology
may include descriptions of
classes
,
properties
and their instances.
What is Ontology…...
an ontology is a formal, explicit specification of a shared conceptualization – Gruber
‘Conceptualization
’ refers to an abstract model of phenomena in the world by having identified the relevant concepts of those phenomena .
‘
Explicit
’ means that the type of concepts used, and the constraints on their use are explicitly defined.
‘
Formal
’ refers to the fact that the ontology should be machine readable.
‘
Shared
’ reflects that ontology should capture consensual knowledge accepted by the communities
Example: Cars Ontology with RDF Schema Semantics
} @cars { xyz:MotorVehicle[rdfs:subClassOf -> rdfs:Resource].
xyz:PassengerVehicle[rdfs:subClassOf -> xyz:MotorVehicle].
xyz:Truck[rdfs:subClassOf -> xyz:MotorVehicle]. xyz:Van[rdfs:subClassOf -> xyz:MotorVehicle].
xyz:MiniVan[ rdfs:subClassOf -> xyz:Van; rdfs:subClassOf -> xyz:PassengerVehicle]. FORALL X < X[rdfs:subClassOf -> xyz:MotorVehicle]@cars.
FORALL X < X[rdfs:subClassOf -> xyz:MotorVehicle]@rdfschema(cars).
xyz:Van xyz:MotorVehicl e xyz:Truc k xyz:PassengerVehicl e xyz:MiniVan
X = xyz:Van X = xyz:Truck X = xyz:PassengerVehicle X = xyz:Van X = xyz:Truck X = xyz:PassengerVehicle X = xyz:MiniVan
OIL
OIL adds a simple Description Logic to RDF Schema It allows to define axioms that logically describe classes, properties and their hierarchies OIL enables to define necessary and sufficient conditions that define class membership of instances
O
IL
OIL Developed in the Ontoknowledge project www.ontoknowledge.org
Core language contains consensus primitives, extensions add aditional expresiveness Layered architecture: • Applications are not forced to work with a language more complex and expresive than required • Applications that can only process a low level of complexity are able to catch the aspects of the ontology • Applications aware of higher level of complexity can still understand a simpler ontology language
Description Logic
: Formal Semantics & Reasoning support
OIL Web languages
: XML- and RDF-based syntax
Frame-based systems
: Epistemological Modeling Primitives
DAML+OIL
DAML+OIL
Semantic markup language Joint efford of the American and European communities DAML+OIL = DAM-ONT + OIL Designed to describe the structure of a domain in terms of classes and objects Supports full range of datatypes in XML
An Example (from www.daml.org)
Start of an
ontology (about = “” implies ‘this’ document)
The label is not used for logical interpretation
This class of animals is illustrative of a number of ontological idioms.
Can explicitly specify the set of Females to be disjoin The Person class is defined later To be read t with the set of Males conjunctively ‘Person’ and a ‘Male’ . A man is a sub-class of
Example (contd..)
Restrictions on the property hasParent (only for the Person class – Local scope, as opposed to rdfs:range) A person can have only another Person as it’s parent A Person can have only 1 Father
Example (contd..)
Classes: intersectionOf (a daml:collection), unionOf (a daml:collection), sameClassAs, complementOf, etc.
OWL
OWL Under development of W3C Web Ontology Working Group DAML+OIL based Offers: • More accurate web searches • Intelligent agents • Knowledge management Abstract syntax that provides: • Higher level way of writing ontologies • Clear statement of semantics • Compound axioms resembling frames OWL-lite OWL sublanguage OWL-lite = RDFs + 0/1 cardinality Suites well to express light weight ontologies Limited expresiveness power • Some fields require a full-fledged semantic web modeling language
OWL Example
unionOf rdf:parseType="Collection">
adjacentRegion
rdf:resource="
#SonomaRegion
" />
Event:title
Title “WWW 2002…” TimBL rdf:type w3c-ont:person; name “Tim Berners … 11”, Lee” g/ontologies/swrc-onto-2000-09 10.daml#Event"/> Claims can be verified if there is supporting evidence from another (trusted) source We only believe that someone is a professor at a university if the university also claims that person is a professor, and the university is on a list I trust. believe(c1) :- claims(x, c1) ^ predicate(c1, professorAt) ^ arg1(c1, x) ^ arg2(c1, y) ^ claims(c2, y) ^ predicate(c2, professorAt) ^ arg1(c2, x) ^ arg2(c2, y) ^ AccreditedUniversity(y) AcknowledgedUniversity(u) :- link-from( “ http://www.cs.umd.edu/university-list” , u) Notice this one A QL defines primitives for queries and answers - A query can be a set of sentences containing some variables - Adding the ability of representing variables into different RLs different QLs; produces - QL is usually related to a RL; Some query languages are: SiLRI (Simple Logic-based RDF Interpreter) - RDQL (RDF Query Language) - TRIPLE - DQL (DAML Query Language) finds resources from given URI having age more than 24 SELECT ?resource WHERE (?resource info:age ?age) AND ?age >= 24 USING info FOR finds the family name and given name from any vcards with formatted name (FN) "John Smith". SELECT ?family , ?given WHERE (?vcard vcard:FN "John Smith") (?vcard vcard:N ?name) (?name vcard:Family ?family) (?name vcard:Given ?given) USING vcard FOR “http://www.w3.org/2001/vcard-rdf/3.0#” User browser query agent Index data base web page rules Knowledge representation scheme RSS “How many train lines are there in Tokyo?” 73 answers found Google document search finds 235,312 possible page hits. Http://www…jp/JRTrains.html claims the answer is 27 A database entitled “ JRTLDB” can be queried for the answer, but you will need “Japanese Railroad Access Code.” A computer program that can compute that number is offered by the Tokyo Digital City information analysis, program. click here to run ... RDF Site Summary (RSS) is a lightweight multipurpose extensible metadata description and syndication format. RSS is an XML application An RSS summary, at a minimum, is a document describing a "channel" consisting of URL-retrievable items . Each item consists of a title, link , and brief description . "Rich Site Summary“ Version .91 "RDF Site Summary“ Version 1.0 "Really Simple Syndication" Version 2.0 RSS Blogs – summaries of daily blog posts Newsletters – synopses of newsletters alerting users that a new newsletter is available Weather Alerts – notification of severe weather Press Announcements – new product announcements Specials or Discounts – weekly deals or discount offers for customers Calendars – listings of upcoming events, deadlines or holidays Semantic Web Application Platform British Telecom Call Center (ontoShare) Swiss Life Application EnerSearch Applications finding and comparing numerous and heterogeneous data formats numerous and heterogeneous business logics … Web of Trust
Query Languages
RDQL Examples
How it may work
Semantic Web - Language tower
Applications
Web Query
(RDF Site Summary)
Knowledge Management
Electronic Commerce
Pervasive Computing
Web queries - for real!!
* Query processed:
RSS
RSS History
RSS Example
Common uses for
Knowledge Management
SWAP
On-to Knowledge
Electronic Commerce
Mechanized support is needed in
vendors and their offers.
Mechanized support is needed in dealing with
.
Mechanized support is needed in dealing with
.
Services off the desktop
Or perhaps on different desktops
The Semantic Web: What is it?
Many things to many people..
Thank you for the attention!
Questions?