declarative languages for querying portal catalogs

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ICS-FORTH & Univ. of Crete Christophides Vassilis December 2000

Declarative Languages for QueryingPortal Catalogs

V. ChristophidesD. Plexousakis

G. KarvounarakisS. Alexaki

Computer Science Department, University of CreteInstitute for Computer Science - FORTH

Heraklion, Crete

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What is a Community Web ?

n A group of people sharing a domain of discourse and a set of information resources (e.g., data, documents, services) and having some common interests

gCommerce, Education, Health

n The main requirement is to provide a single point of useful, ubiquitouscomprehensive, and integrated accessto various information resources

gWeb Portals

C-Web

Education

HealthCommerce

Workplace

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Portals Classification

On-line Communities

Existing Communities

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Portals Classification

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Generating new knowledge

Accessing knowledge from external sources

Representing knowledge in documents and databases

Embedding knowledge inservices and processes

Dissemination of knowledge within organisation

Using knowledge in decision making

Knowledge Processes in Corporate Communities

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Advanced Knowledge Schemas

(ontologies, thesauri)

<tag1><tag2><tag3>

</tag1>

<tag1><tag2><tag3>

</tag1>

Complexity and diversity

of information resources

Heterogeneous

resource descriptions

Community Web Portals: Main Features

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What we need?

n Flexible Modeling of Community Web Portal Catalogsu Exploit existing forms of community knowledge

• Ranging from simple vocabularies to formal ontologies

v Describe in various ways community information resources• Administration, Classification, Content Rating, Channels, ….

n Secondary Storage Management of Portal Metadatau Large Schemas: e.g., 100 Mbytes of ODP Topics (the Art Hierarchy

contains 20000 terms)

v Voluminous Description Bases: e.g., 700 Mbytes of ODP indexed URLs

n Declarative Query Languages for Portal Catalogsu Interleave schema with data querying

v Optimize access to Portal Catalogs

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Our Approach

High-level Access to

community information

Archives

Virtual XML Warehouse

Documents

Databases

Web

RDF

Å Use W3C Standards to describe (RDF/S) & exchange (XML) information

Å Our Contribution: Declarative Languages for Browsing & Querying

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Outline

n Example of a Portal Catalog for Cultural Communities

n Describing and Querying Community ResourcesgA Formal Data Model for RDF/SgThe RDF Query Language (RQL)

n ArchitecturegCore Middleware (RDF Store, Parser/Loader, Query Interpreter)

n Build Community Web PortalsgCreate/Extract Resource MetadatagDevelop Specific Applications for CommunitiesgOptimize RDF Storage and Queries

n Summary

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Building a Cultural Community Web Portal using RDF

r2: museoreinasofia.mcu.es/guernica.jpg

r1:www.rodin.fr/thinker.gif

PortalSchema

PortalResourceDescriptions

ExtResource

last_modified title

StringDate

“oil on canvas”technique

exhibited

“Reina Sofia Museum”

title2000/06/09

last_modified

&r3

&r1

&r2

&r4

Artist

Sculptor

StringArtifact

Sculpture

Painting

sculpts

createsfname

lname

paints

StringMuseumexhibited

techniqueStringPainter

paints

creates

&r5

&r6

fname

lname

lname

paints

“Pablo”

“Picasso”

“Rodin”

2000/01/02last_modified

r4:museoreinasofia.mcu.esr3:www.artchive.com/woman.jpg

Web Resources

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Resource Description Framework (RDF/S)

n RDF: Resource Descriptions gData Model: Directed Labeled Graphs

• Nodes: Resources (URIs) or Litterals• Edges: Properties – Attributes or Relationships• Labels: Nodes (Class names) and Edges (Property names)• Statement: assertion of the form resource, property, value• Description: collection of statements concerning a resource

gXML syntaxn RDF Schema (RDFS): Schema Vocabularies

gSpecialization of both classes & properties (simple & multiple)gMultiple classification under several classesgUnordered, optional, and multi-valued properties gDomain and range polymorphism of properties

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RDF/XML Serialization: Data<rdf:RDF xml:lang="en"

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:rdfs="http://www.w3.org/TR/2000/PR-rdf-schema-20000327#"xmlns="">

….

<Painter rdf:id=“picasso132"><fname>Pablo</fname><lname>Picasso</lname><paints>

<Painting rdf:about="http://museoreinasofia.mcu.es/guernica.gif"><exhibited>

<Museum rdf:about="http://museoreinasofia.mcu.es"/></exhibited ><technique>oil on canvas</technique>

</Painting></paints><paints>

<Painting rdf:about="http://www.artchive.com/woman.jpg”/></paints>

</Painter><ExtResource rdf:about="http://museoreinasofia.mcu.es">

<title>ReinaSophia Museum</title ><lastmodified>2000/06/09</lastmodified>

<Sculptor rdf:id="rodin424" lname="Rodin “><creates>

<Sculpture rdf:about="http://www.rodin .fr/thinker.gif"/></creates>

</Sculptor></rdf:RDF>

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RDF/XML Serialization: Schema<rdf:RDF xml:lang="en"

xmlns:rdf="http://www.w3.org/1999/02/ 22-rdf-syntax-ns#"

xmlns:rdfs="http://www.w3.org/TR/2000/ PR-rdf-schema-20000327#"><rdfs:Class rdf:ID="Artist"/><rdfs:Class rdf:ID="Artifact"/><rdfs:Class rdf:ID="Style"/><rdfs:Class rdf:ID="Sculptor"><rdfs:Class rdf:ID=“Museum">

<rdfs:subClassOf rdf:resource="#Artist"/> </rdfs:Class><rdfs:Class rdf:ID="Painter">

<rdfs:subClassOf rdf:resource="#Artist"/> </rdfs:Class><rdfs:Class rdf:ID="Sculpture">

<rdfs:subClassOf rdf:resource="#Artifact"/> </rdfs:Class><rdfs:Class rdf:ID="Painting">

<rdfs:subClassOf rdf:resource="#Artifact"/> </rdfs:Class><rdf:Property rdf:ID="creates ">

<rdfs:domain rdf:resource="#Artist"/><rdfs:range rdf:resource="#Artifact"/>

</rdf:Property>

<rdf:Property rdf:ID="paints"><rdfs:domain rdf:resource="#Painter"/><rdfs:range rdf:resource="#Painting"/><rdfs:subPropertyOf rdf:resource="#creates"/>

</rdf:Property><rdf:Property rdf:ID="sculpts">

<rdfs:domain rdf:resource="#Sculptor"/><rdfs:range rdf:resource="#Sculpture"/><rdfs:subPropertyOf rdf:resource="#creates"/>

</rdf:Property><rdf:Property rdf:ID=“exhibited ">

<rdfs:domain rdf:resource="#Painting"/><rdfs:range rdf:resource=“#Museum"/>

</rdf:Property><rdf:Property rdf:ID=" technique">

<rdfs:domain rdf:resource="#Painting"/><rdfs:range rdf:resource="http://www.w3.org/

TR/1999/PR-rdf-schema-19990303#Literal"/></rdf:Property><rdf:Property rdf:ID="title">

<rdfs:domain rdf:resource="#ExtResource"/><rdfs:range rdf:resource= "http://www.w3.org/

TR/1999/PR-rdf-schema-19990303#Literal"/></rdf:Property> ….</rdf:RDF>

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RDF/S vs. Well-Known Formalisms

n Relational or Object Database Models (ODMG, SQL)g Classes don’t define table or object typesg Instances may have associated quite different propertiesg Collections with heterogeneous members

n Semistructured or XML Data Models ( Ï Å Ì, UnQL, YAT, XML Schema)

g Labels only on nodes or edgesg Class and property subsumption is not capturedg Heterogeneous structures reminiscent to SGML exceptions

n KR Languages (Telos, DL, F-Logic)g Absence of complex values and n-ary relationships (bags, sequences)g Inadequate reasoning support

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A Formal Data Model for RDF

n Ç(Í,<) is a well-defined hierarchy of classes/properties iff:

gc ∈ C => c < Class

gp ∈ P => p < Property

gp1,p2 ∈ P and p1 < p2 => domain(p1) ≤ domain(p2) and range(p1) ≤ range(p2)

n Type System:

τ = τL | τU | {τ} | [τ] | (1:τ + 2:τ + … + n:τ)

n Interpretation Function:gLiteral types, [[ τL ]] = dom(τL)

gBag types, [[ {τ} ]] = {ν1, ν2,…, νn}, ν1, ν2,…, νn ∈ V are values of type τ

gSeq types, [[ [τ] ]] = {ν1, ν2,…, νn}, ν1, ν2,…, νn ∈ V are values of type τgAlt types, [[ (1:τ1 + 2:τ2 +…+ n:τn ) ]] = νI, νi ∈ V, 1<i<n is a value of type τi

gc ∈ C, [[c]] = {ν | ν ∈ π(c)}∪{π(c’) | c’ < c}

gp ∈ P, [[p]] = {[ν1, ν2] | ν1 ∈ [[domain(p)]], ν1 ∈ [[range(p)]]}∪{π(p’) | p’ < p}

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n An RDF schema is a 5-tuple: RS = (VS, ES, H, ψ, λ)gVS a set of nodesgES a set of edgesgÇ = (Í,<) a well-formed hierarchy of names

gλ a labeling function: VS ∪ ES → Í ∪Ôgψ an incidence function: Es → Vs×Vs

n An RDF description base, instance of a schema RS, is a 5-tuple: RD = (VD, ED, ψ, ν, λ)

gVD a set of nodesgED a set of edges

gψ an incidence function: ED → VD×VD

gν a valuation function: VD → Vgλ a labeling function: VD ∪ ED →2 Í∪Ô:

• ∀ u ∈ VD, λ → n ∈ C∪T: ν(u) ∈[[n]]• ∀ e ∈ ED [u,u’], λ → p

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resources

URI

U V

λλ

T

[[ . ]]

PropertyClass< <

ττCττL ττP

ψψ

ππ{[val,val}]

container

[[ . ]]

νν

λλN

H

S

val

ττ{} ττ[]

ννliterals

νν

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The RDF Query Language

n Declarative query language for RDF description basesgrelies on a typed data model (literal & container types + union types)gfollows a functional approach (basic queries and filters)gadapts the functionality of semistructured or XML query languages to

RDF, but also: • treats properties as self-existent individuals• exploits taxonomies of node and edge labels • allows querying of schemas as semistructured data

n Relational interpretation of schemas & resource descriptionsgClasses (unary relations)gProperties (binary relations)

gContainers (n-ary relations)

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Browsing Portal Catalogs with RQL

n Simple set queries on class and property extents:gFind the resources in the extent of the property creates

createsØ {{ [www.portal.gr/rodin424, www.rodin.fr/thinker.gif],

[www.portal.gr/picasso132, museoreinasofia.mcu.es/guernica.gif],[www.portal.gr/picasso132, www.artchive.com/woman.jpg] }}

gFind the resources of type painter and sculptorExtResource intersect Sculpture

Ø {{ www.rodin.fr/thinker.gif }}

n Schema constructs used as query terms & support for automatic

query expansion (similar to thesauri-based IRS)

gUseful to query resources with minimal schema knowledge

Includes paints & sculpts

Multiply classified resources

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Personalizing Portal Catalogs with RQL

n Navigational queries on semistructured resource descriptionsgFind the Museum resources that have been modified in year 2000.select xfrom Museum{x}.last_modified{y}where y >= 2000/01/01

Ø {{museoreinasofia.mcu.es}}

hSimilar functionality to semistructured or XML query languages (Lorel,UnQL, XQL, XML-QL, XML-GL)§ Useful in the absence of schema information or when multiple

schemas are used to describe resources

Data paths not foreseen in the schema

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Querying Portal Catalogs with Large Schemas

n Filtering both resource descriptions and schemasgFind the paintings having as technique “oil on canvas” that have

been created by a neo-impressionist painter

select yfrom {:$X}creates{y:Painting}.technique{z}where $X <= neo-impressionist and z = “oil on canvas”

Data filtering with schema information

Schema Filtering on Class hierarchies

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Querying Portal Schemas with RQL

n Pure schema queriesgFind the properties which specialize the property creates and may

have as domain the class Painter along with their corresponding range classesselect @P, $Yfrom {:Painter}@P{:$Y}where @P <= creates

Ø {{ [creates, Artifact],[creates, Painting],[creates, Sculpture],[paints, Painting] }}

Schema filtering onproperty hierarchies

All Properties defined orinherited in class Painter

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RQL: Examples

ns1#creates

ns1#Painter

ns1#Artifact

ns1#Painting ns1#Sculpture

ns1#paints

ns1#Painter ns1#Painting ns1#Sculpture

ns1#paints

ns1#creates

ns1#Artist

ns1#Painter ns1#Sculptor

String

Stringns1#Artifact

ns1#Painting ns1#Sculpture

ns1#Style

String

ns1#paints

ns1#creates ns1#has_style

ns1#has_material

ns1#fname

ns1#lname

ns1#sculpts odp#ExtPagedc#last_modified

Date

ns1#Impressionist

ns1#PostImpressionist

ns1#Painter ns1#Painting ns1#Sculpture

ns1#paints

ns1#creates

h Similar functionality to DBMS schema QLs (SchemaSQL, XSQL)§ Useful for large schemas (integrating ontologies and thesauri)

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Putting it all Together

n Nested schema and data queriesgFind the resources modified after 2000/01/01 which can be reached

by a property applied to the class Painting and its subclassesselect R, yfrom (select @P

from {:$X}@Pwhere $X <= Painting){R}.{y}last_modified{z}

where z >= 2000/01/01

Ø {{ [exhibited, museoreinasofia.mcu.es] }}

n Subcommunities may use different schemas while sharing the same description base

R ranges over the labelsof type property

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RQL:Examples

PortalSchema

PortalResourceDescriptions

“oil on canvas”technique

exhibited

&r3

&r2

&r4

Painting

Museumexhibited

techniqueString



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Putting it all Together

n Schema and data queriesgFind all metadata about the resources of the site museoreinasofia.mcu.es

select x,$$Y,$P,z,$$Wfrom {x:$$Y}$P{z:$$W}where x like “*museoreinasofia.mcu.es*” or

y like “*museoreinasofia.mcu.es*”

Ø {{[www.portal.gr/picasso132, Painter, paints, museoreinasofia.mcu.es/guernica.gif, Painting],

[museoreinasofia.mcu.es/guernica.gif, Painting, exhibited, museoreinasofia.mcu.es, Museum],[museoreinasofia.mcu.es/guernica.gif, Painting, technique, “oil on canvas”, string], [museoreinasofia.mcu.es, ExtResource, title, “Reina Sophia Museum”, string], [museoreinasofia.mcu.es, ExtResource, last_modified, 2000/06/09, date], ….}}

n Subcommunities may use both different schemas and description bases

URLs’ pattern matching

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The Core Portal Middleware

Parser

VRP InternalRDF Model

Validator

RD

F Lo

ader

Load

ing

RD

F Ja

va A

PIsICS-VRP

JDBC

Class Property

ORDBMS

DBM

S RD

F qu

ery

API

SQ

L3+

SP

I fun

ctio

ns

LIBC++

p_namedomain range

Artist creates Artifact

c_name

Artist

URI

creates

subcl

Painter

supcl

Artist

subpr

paints

suppr

creates

SubClassSubProperty

source

paints

target

creates

Artist creates

SQL3 SQL3

ICS-RQL Interpreter

Typing

Evaluation

GraphConstructor

Parser

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The ICS-FORTH R&D Activitieshttp://www.ics.forth.gr/proj/isst/RDF

n The Validating RDF Parser (VRP): Karsten Tolle Diploma Thesis

gThe First RDF Parser supporting semantic validation of both resource descriptions and schemas

n The RDF Schema Specific DataBase (RSSDB): Sophia Alexaki Ms. Thesis

gThe First RDF Store using schema knowledge to automatically generate an Object-Relational (SQL3) representation of RDF metadata and load resource descriptions

n The RDF Query Language (RQL): Greg Karvournarakis Ms. Thesis

gThe First Declarative Language for uniformly querying RDF schemas and resource descriptions

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Architecture of Community Web Portals

Query Engine

Session Manager

URL ResolverMetadata

Store

Painter

Museum

Painting

XML WrapperResourcesXMLXML

Logical Middle Tier

CWEB/Application Server

Other docs

news, reports

on the Intranete.g. mails,

Well-formedXML docson the Web

XML

XML enabledDBMS

Client Tier

SchemaGenerator

RDF/XMLLoader

XML/XSLProcessor

ResourceDescription

Interface

Query BrowsingInterface

Artist

XML/XSL

Middleware APIs

http

http

Artist

URL

RDF/XMLSchema

RDF/XMLDescriptions

RQL

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Describing Community Information Resources

Automatic AutomaticAutomaticManagement(all kinds)

Manual Manual ManualStructure Descriptive(semistructured,

structured)

Automatic Query MediationQuery MediationManualContent Descriptive(unstructured,semistructured,

structured)

CollectionStatic Dynamic

IndividualMetadata TypeResources Nature

Sem

antic

sS

ynta

xS

yste

m

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Related Work

n Information Integration Systemsg YAT (INRIA Verso) www-rocq.inria.fr/~simeon/YATg MIX (San Diego) www.db.ucsd.edu/projects/MIXg TSIMMIS (Stanford) www-db.stanford.edu/tsimmisg GARLIC (IBM) www.almaden.ibm.com/cs/garlicg DISCO (INRIA Caravel) rodin.inria.fr/Eprototype_Disco.htmlg DIOM (Alberta, Canada) ugweb.cs.ualberta.ca/~diomg Nomenclator (Bell Labs) cm.bell-labs.com/cm/cs/what/nomenclatorg MANIFOLD (AT&T) www.research.att.com/~levy/imhome.htmlg Picsel (ORSAY) www.lri.fr/~picselg CoBase (California) cobase-www.cs.ucla.edug Momis (Modena, Italy) sparc20.dsi.unimo.it/Momisg InfoHarness & InfoQuilt (Georgia) lsdis.cs.uga.edu/proj/proj.htmlg Infomaster (Stanford) infomaster.stanford.edu/infomaster-info.htmlg InfoSleuth (MCC,Texas) www.mcc.com:80/projects/infosleuthg Ariadne (Southern California) www.isi.edu/ariadneg SIMS (Southern California) www.isi.edu/simsg HERMES (Maryland, College Park) www.cs.umd.edu/projects/hermesg Carnot (MCC,Texas) www.mcc.com:80/projects/carnot

n Main Focus on structured and semi-structured data integration

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Related Work

n Ontology-based Information SystemsgOn-To-Knowledge (IST-1999-10132) www.ontoknowledge.org

gIBROW (IST-1999-19005) www.swi.psy.uva.nl/projects/ibrow/home.html

gOntoSeek (Padova, Italy) www.ladseb.pd.cnr.it/infor/ontology/ontology.html

gObserver (Basque Country, Spain) siul02.si.ehu.es/~jirgbdat/OBSERVER

gOntological Mediation (New York at Buffalo) www.cs.buffalo.edu/~aec/OM

n Main Focus on knowledge integration

n Ontology-driven Document Annotation SystemsgOntobroker (Karlsruhe, Germany) ontobroker.aifb.uni-karlsruhe.de

gSHOE (Maryland, College Park) www.cs.umd.edu/projects/plus/SHOE

gWebKB (Griffith, Australia) meganesia.int.gu.edu.au/~phmartin/WebKB

gOHTML, XAL

n Main Focus on intelligent document access

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Related Work

n Corporate Knowledge Management and Ontological Engineering gCommonKADS (ESPRIT P5248) www.swi.psy.uva.nl/projects/CommonKADS

gCyc (MCC,Texas) www.mcc.com:80/projects/cyc

gTOVE (Toronto) www. eil.utoronto.ca/eil.html

gEnterprise (DTI, ISIP Programme) www.aiai.ed.ac.uk/~entprise

gKactus (ESPRIT Project 8145) www.swi.psy.uva.nl/projects/Kactus/home.html

gKRAFT (Liverpool , U.K.) www.csc.liv.ac.uk/~kraft

gO-Plan (Edinburgh , U.K.) www.aiai.ed.ac.uk/~oplan

gGeneralized Upper Model (GMD) www.darmstadt.gmd.de/publish/komet/gen-um/newUM.html

gONTOINT (CNR, Rome, Italy) saussure.irmkant.rm.cnr.it/onto/ontoint.html

gPlanetOnto (Open University, U.K.) kmi.open.ac.uk/projects/planetonto

n Main Focus on domain modeling and knowledge representation

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Related Work

n Digital LibrariesgElectronic Environmental DL (Berkeley) elib.cs.berkeley.edugInformedia (Carnegie-Mellon) www.informedia.cs.cmu.edugInterspace (Illinois) dli.grainger.uiuc.edugUMDL (Michigan) www.si.umich.edu/UMDLgDL Technologies (Stanford) www-diglib.stanford.edugAlexandria (Santa Barbara) alexandria.sdc.ucsb.edugADEPT (Georgia) lsdis.cs.uga.edu/~adeptgERCIM DELOS DL (Europe) www.ercim.org/delosgUKOLN (U.K.) www.ukoln.ac.ukgCIDL (Canada) www.nlc-bnc.ca/cidlgWaikato (New Zealand) www.cs.waikato.ac.nz/cgi-bin/nzdlbeta/gw

n Main Focus on system infrastructure for global information sharing

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Summary and Future Work

n Our contribution:gFirst declarative language for uniformly querying RDF schemas and

resource descriptionsgFormal model for RDF/S (+ typed, operational semantics)

n Functionality evaluation:gDeveloped in the context of the EC project C-Web (http://cweb.inria.fr)gAccepted for use in the ongoing EC projects:

• MesMuses (http://aquarelle.inria.fr/mesmuses)• Ontoknowledge (http://www.ontoknowledge.org)

n Performance evaluation:gTestbed: Open Directory RDF dump

• 321,988 Topics (~100M), 2,123,382 Sites (~700M)gOptimization opportunities:

• Schema and Data Indexing Techniques (transitive closure queries)

• Heuristics for Algebraic Transformations (schema and data queries)