foundations of the semantic web rocky dunlap college of computing georgia tech advisors: spencer...
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Foundations of the Semantic Web
Rocky DunlapCollege of ComputingGeorgia Tech
Advisors:Spencer RugaberLeo Mark
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Things we can talk about
Earth System CuratorIncluding a short demo
Semantic Web......versus today’s Web...theoretical foundations...application areas
Implications for LogicBloxHow could SW technologies be useful
for LogicBlox?
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The short story on Curator
Problem statement Model-generated datasets in the climate community
lack metadata that is required for understanding and analyzing the dataset
Premise The descriptors used for comprehensively specifying
a model configuration are also needed for a scientifically useful description of the model output data
Solution Develop a standardized metadata formalism for
describing climate datasets that is based on the model configuration used to generate the dataset
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The Google Way
Keyword search...• Good for expert users who are familiar with the datasets
But...• Many details of what went into the dataset left out• Not machine-readable (e.g., by analysis tools)• Limited standardization• Not semantic or conceptual in nature
10 lines of metadataRun script: 1500+ lines plus input files
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NASA GEOS-5 Model
GEOS-5
surface fvcore gravi ty_wave_drag
history agcm
dynamics physics
chemistry moist_processes radiation turbulence
infrared solar lake land_ice data_ocean land
vegetation catchment
coupler
coupler coupler
coupler
coupler
coupler
coupler
http://gmao.gsfc.nasa.gov/systems/geos5/
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Demo
http://cdp.ucar.edu:28080/query/queryESC.htm
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Demo
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Beyond Curator
Curator is a representative projectE-science communities are emerging
in many areas of science Prediction
Scientific data management -- an emerging area that will continue to grow
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Today’s Web
Primarily intended for human consumption
Lots of content, but very little about what the content means
One relationship: the hyperlinkNo semantics really
HTML is almost completely about presentation
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HTML<html> <body> <h1>Rocky’s Pizzeria</h1> <h2>Where you make your own pizza pie!</h2>
<b>Crust options:</b> <ul> <li>Deep Pan</li> <li>Thin and Crispy</li> </ul>
<br/>
<b>Toppings:</b> <ul> <li>Mozzarella</li> <li>Anchovies</li> ....
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(Non-semantic) Hyperlinks
<html>
</html>
<html>
</html> <html>
</html>
<html>
</html>
<html>
</html>
<html>
</html>
<html>
</html>
<html>
</html> <html>
</html>
<a href=“http://www.logicblox.com/”>Home Page</a>
??
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The Semantic Web
Not a new webA layer on top of the existing web
Web-based content should be annotated with explicit semantics
Intended primarily for machine-consumption, i.e., “intelligent agents”
Markup for describing meaning of content, not just presentation
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Giving meaning to content<restaurants> <restaurant> <name>Rocky’s Pizzeria</name> <description>Where you make your own pizza pie!</description> <phone>404-123-4567</phone> <address>123 Peachtree Street</address>
<menu choice=“crust”> <option>Deep Pan</option> <option>Thin and Crispy</option> </menu>
<menu choice=“toppings”> <option>Mozzarella</option> <option>Anchovies</option> </menu> <restaurant></restaurants>
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Semantic Links
<html>
</html>
hasReview
hasPhotoAlbum
hasNewVersion
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SW Application Areas
Semantic interoperability and data integration health care, drug industry, e-science
Semantic search Can we outsmart Google?
Specific areas: Geographic Information Systems B2B Mediation Legal Automobile diagnostics and repair
http://www.w3.org/2001/sw/sweo/public/UseCases/
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SW Technology Stack
HTTP, URIs
Internet
XML, XML Schema
RDF(S)/OWL
Rules
Reliable transport
Hypertext transfer
Structured data transfer
Conceptual descriptions
Technology What it provides
Advanced reasoning
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SW Ontology Languages
Resource Description Framework (RDF)1
Provides the ability to make statements (propositions) about resources on the web
Web Ontology Language (OWL)2
More expressive features than RDFStrong theoretical basis on
Description Logics
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RDF Statements
“The Curator meeting is at GFDL.”
Curatormeeting GFDL
hasLocation
subject predicate object
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RDF Statements
“The Curator meeting is Oct 18-19.”
Curatormeeting GFDL
“18 Oct 2007”
“19 Oct 2007”
hasLocation
starts
ends
resource
literal
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RDF Statements
“Balaji works at GFDL.”
Curatormeeting GFDL
“18 Oct 2007”
“19 Oct 2007”
Balaji
hasLocationworksAt
starts
ends
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RDF XML Representation
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:esc="http://www.earthsystemcurator.org">
<rdf:Description rdf:about=“http://....#OctCuratorMeeting"><esc:hasLocation rdf:resource=“http://....#GFDL”/><esc:starts>18 Oct 2007</esc:starts><esc:ends>19 Oct 2007</esc:ends>
</rdf:Description>
<rdf:Description rdf:about=“http://....#Balaji"><esc:worksAt rdf:resource=“http://....#GFDL”/>
</rdf:Description>
</rdf:RDF>
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RDF Schema
Define a domain specific data model for RDFIncludes classes and properties (along
with subclasses and subproperties)Properties are first class (they are not
defined as part of a particular class)
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RDF Schema
ClassesProperties
Event
MeetingFlight
Person
hasLocation domain: Event range: Place
starts domain: Event range: date
Place
ends domain: Event range: date
worksAt domain: Person range: Place
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OWL (Web Ontology Language)
Motivations Expressive ontology language Precise semantics
• Understanding of formal properties such as decidability and complexity of inferencing
Ease of use for a wide audience Influences
DAML+OIL (existing language) Description Logics Frames paradigm
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Description Logics
“A formal language for representing knowledge and reasoning about it.”3
“Description”Primary facilities are concept and role
descriptions “Logics”
Equipped with a FOL-based formal semantics
Inference procedures reveal implied knowledge
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DL Knowledge Base
TBoxContains the terminology, i.e., the
vocabulary of an application domain, i.e., concepts and roles
Think database schema ABox
Contains the assertions about named individuals
Think database data
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In the TBox
Two symbols atomic concepts (A, B) atomic roles (R)
Complex descriptions through concept constructors (C, D) role constructors
Concept and role constructors determine: The expressiveness of the DL Decidability/complexity of reasoning
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C A | (atomic concept)
| (universal concept)
| (bottom concept)
A | (atomic negation)
C D | (intersection)
R.C | (value restriction)
R. (limited existential quant.)
DL Language ALA
E
Grammar for concept construction
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DL Language AL
Atomic concepts: Food, Pizza, CheeseToppingAtomic role: hasTopping
“Non-pizza foods”Food Pizza
“Pizza with only cheese toppings”Pizza hasTopping.CheeseTopping
“Pizza with some topping”Pizza hasTopping.
A
E
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Name Syntax Symbol
Union C D U
Existential quant. R.C E
Unqual. cardinality restriction ≥ n R, ≤ n R, = n R N
Qual. cardinality restriction ≥ n R.C, ≤ n R.C, = n R.C Q
Role hierarchy R S H
Inverse properties R- I
Functional properties F
Nominals (enumeration) O
DL Concept/Role Constructors
E
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Pizza(x) y.hasTopping(x,y) CheeseTopping(y)
Pizza(x) y.hasTopping(x,y)
Pizza(x) y.hasTopping(x,y) CheeseTopping(y)
Pizza hasTopping.CheeseTopping
Food(x) Pizza(x)
Food Pizza
FOL Representations
A
A
Pizza hasTopping.
E
E
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In the ABox
Assertions about individuals
Pizza(p1)Pizza(p2)CheeseTopping(mozzarella)CheeseTopping(goatCheese)hasTopping(p1, mozzerella)hasTopping(p1, goatCheese)hasTopping(p2, goatCheese)
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Reasoning on the KB
TBox Concept satisfiability
• Are there possible instances?
Concept subsumption• Is concept C almost more general than D?
Concept equivalence ABox
Instance checking• Is individual X an instance of concept C?
Consistency checking• Is individual X a possible model of the TBox?
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From DL to OWL
OWL has three “species” or dialects OWL-DL equivalent to DL SHOIN(D) OWL-Lite equivalent to DL SHIF(D) OWL-Full -- messy...
Must adhere to constraints of the Web Standard XML syntax URIs for identifying concepts, roles, and
individuals Concrete datatypes based on XML Schema
Protégé Demo4
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Adding Rules to OWL
Semantic Web Rule Language (SWRL)5
hasParent(?x,?y) hasBrother(?y,?z) hasUncle(?x,?z)
Artist(?x) artistStyle(?x, ?y) Style(?y) creator(?z,?x) style/period(?z, ?y)
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Semantic Web Apps
DBPedia Convert Wikipedia articles into RDF
Freebase Wikipedia + semantic links
Twine Social networking + semantic web
GeoNames Ontology of geospatial semantic information
WordNet Ontology RDF/OWL representation of WordNet
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Discussion
Implications for LogicBlox?
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References
[1] Manola, et. al. RDF Primer. http://www.w3.org/TR/rdf-primer/
[2] McGuiness, et al. OWL Web Ontology Language Overview. http://www.w3.org/TR/owl-features/
[3] Baader, et. al. The Description Logic Handbook, 2007.
[4] Horridge, at. al. A Practical Guide To Building OWL Ontologies Using the Protégé-OWL Plugin and CO-ODE Tools, Edition 1.0., 2004. http://www.co-ode.org/resources/tutorials/ProtegeOWLTutorial.pdf
[5] Horrocks, et. al. SWRL: A Semantic Web Rule Language Combining OWL and RuleML. http://www.w3.org/Submission/SWRL/
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AE