foundations of the semantic web rocky dunlap college of computing georgia tech advisors: spencer...

Foundations of the Semantic Web

Rocky DunlapCollege of ComputingGeorgia Tech

Advisors:Spencer RugaberLeo Mark

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?

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

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

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/

Demo

http://cdp.ucar.edu:28080/query/queryESC.htm

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

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

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> ....

(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>

??

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

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>

Semantic Links

<html>

</html>

hasReview

hasPhotoAlbum

hasNewVersion

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/

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

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

RDF Statements

“The Curator meeting is at GFDL.”

Curatormeeting GFDL

hasLocation

subject predicate object

RDF Statements

“The Curator meeting is Oct 18-19.”

Curatormeeting GFDL

“18 Oct 2007”

“19 Oct 2007”

hasLocation

starts

ends

resource

literal

RDF Statements

“Balaji works at GFDL.”

Curatormeeting GFDL

“18 Oct 2007”

“19 Oct 2007”

Balaji

hasLocationworksAt

starts

ends

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>

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)

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

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

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

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

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

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

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

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

In the ABox

Assertions about individuals

Pizza(p1)Pizza(p2)CheeseTopping(mozzarella)CheeseTopping(goatCheese)hasTopping(p1, mozzerella)hasTopping(p1, goatCheese)hasTopping(p2, goatCheese)

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?

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

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)

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

Discussion

Implications for LogicBlox?

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/

foundations of the semantic web rocky dunlap college of computing georgia tech advisors: spencer...

Documents

semantic webnot

content rockys pizzeria

useful description

existing webwebbased

model configuration

content meansone relationship

theoretical foundations

climate datasets