1 ics-forth london 25/01/02 christophides vassilis on community web portals and the semantic web: a...
TRANSCRIPT
Christophides Vassilis
1
ICS-FORTH London 25/01/02
On Community Web Portals and the Semantic Web:
A Database Perspective
Vassilis Christophides Computer Science Department, University of Crete
Institute for Computer Science - FORTHHeraklion, Crete
Christophides Vassilis
2
ICS-FORTH London 25/01/02
Portalmania!
Christophides Vassilis
4
ICS-FORTH London 25/01/02
Elements of Comparison
Gateways to WWW resources with the aim of making information/service research simpler and more effective
Horizontal Portals Vertical or Thematic Portals
E-marketplaces
Scope Internet-oriented Subject-oriented Industry-oriented
Mission reference points for the general user
promote access to information
promote economic activity
Methods voluntary registration; human or robot-driven resource collection
expert selection of resources
voluntary participation by companies
Christophides Vassilis
6
ICS-FORTH London 25/01/02
Common Objectives/Goals Community Knowledge Management
Ranging from simple vocabularies to formal ontologies Aggregation/Integration of Community Content
Ranging from unstructured (documents) to semi-structured (web sites) and structured information (data)
Collaboration & MessagingRanging from simple to advanced task management (synchronous/
asynchronous) System Integration & Security
Front end to application servers/ workflow systems User Personalization (“pull”) & Syndicated Content Subscription (“push”)
role-based access controlinformation filtering (contexts/viewpoints)customizable information rendering location/time specific information
Christophides Vassilis
7
ICS-FORTH London 25/01/02
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: Knowledge Management
Christophides Vassilis
12
ICS-FORTH London 25/01/02
Community Web Portals: A Broader Functional View
Presentation ServicesPresentation Services
Access and Integration ServicesAccess and Integration Services
Information ServicesInformation Services Personalization ServicesPersonalization Services Collaboration ServicesCollaboration Services
ClassificationMetadata
Content Syndication
SecurityNetwork
TaskManagement
Application Integration
SystemManagement
Description, SearchDocs Repositories
Messaging Workflow
Annotations, Recommendations
Multiple Style SheetsVirtual Documents
Christophides Vassilis
17
ICS-FORTH London 25/01/02
On the Semantic Web
Main infrastructure for supporting Community Webs
groups of people sharing a domain of discourse and a set of information resources (e.g., data, documents, services) and having some common interests/objectives
Higher Quality Web Information Services
having data and programs described in a way that facilitates their reuse and integration by machines across applications
Semantic Web
Education
HealthCommerce
Workplace
Christophides Vassilis
18
ICS-FORTH London 25/01/02
Metadata exists for Almost Anything/Everywhere
Physical Objects, Places,
People,
Devices, Networks,
Infrastructure,
Digital Documents, Data,
Programs,
User Profiles, Preferences,
<tag1> <tag2> <tag3></tag1>
<tag1> <tag2> <tag3></tag1>
Christophides Vassilis
19
ICS-FORTH London 25/01/02
RDF Objectives
Enables communities to define their own semantics of resource descriptions
we can disagree about semantics, but share the same infrastructure (syntax, editors, query languages, databases, etc.)
Imposes structural constraints on the expression of metadata in various application contexts
for consistent encoding, exchange and processing of metadata on the Web
Facilitates development of metadata vocabularies without central coordination
mechanisms for reusing descriptions of resources, concepts, etc.
Focus on DBMS technology for RDF metadataRelated W3C efforts on XML data management
Christophides Vassilis
20
ICS-FORTH London 25/01/02
Looking at existing RDF Applications
Publishing/News: BiblinkScholarly Link Specification (Slinks)Rich Site Summary (RSS)
Education/ Academic:Common European Research
Information Format (CERIF)Mathematics InternationalUniversal IMS Global Learning Consortium
Cultural Heritage/ Archives/ Libraries:Inter. Committee for Documentation
Reference Schema (CIDOC)Research Support Libraries – Colle
ction Level Description (RSLP-CLD) EUropean Libraries & Electronic
Resources in Mathematical Sciences (Euler)
Audio-visual: Internet Movie DataBase (IMDB)
Ubiquitous/Mobile/Grid ComputingComposite Capability/Preference
Profile (CC/PP)RDF Calendar Task ForceScheduler Allocation Ontology(SAO)
E-commerceBasic Semantic Registry (BSR)Real Estate Data ConsortiumUniversal Standard Products and
Services Classification (UNSPSC) Geospatial/ Environmental:
Geography Markup Language(GML) Costal Zone Management Ontology
Biology/MedecineGene Ontology
Cross-domain
Christophides Vassilis
21
ICS-FORTH London 25/01/02
Semantic Depth of Resource Descriptions
Dictionaries and Vocabularies: the schemas developed at this level define simple lists of concepts
and their definitions Taxonomies:
their characteristic is that the main relation they define between concepts is that of specialization
Thesauri: besides defining relations among broader/narrower terms through
the definition of hierarchies, a thesaurus also declares relations of equivalence, association and synonymy
Reference Models:comprise a representation vocabulary for referring to the concepts
in the subject area and the logical statements that describe the nature of the terms, the relations among the terms and the way the terms can or cannot be related to each other
Christophides Vassilis
23
ICS-FORTH London 25/01/02
A First Classification of RDF Schemas
Application Domain Dictionary/ Vocabulary
Taxonomy Thesaurus Reference Model
Cultural Heritage/Archives/Libraries
EulerRSLP-CLD
CIDOC
Educational/
Academic
IMSUniversal
Mathematics International
CERIF
Publishing/ News BibLinkSLinkSRSS
Audio-Visual IMDB
Geospatial/ Environmental CZM GML
Biology/ Medicine Gene
E-Commerce BSRUNSPSC
RED
Ubiquitous/ Mobile/Grid Computing
CC/PP RDF CalendarSAO
Cross-Domain CERES/NBIIDublin CoreWordNet
Metanet Limber ThesaurusTop Level Ontology
Christophides Vassilis
24
ICS-FORTH London 25/01/02
Outline
Database issues for RDF metadata managementThe Data Independence IssueThe Query Language IssueThe Model Issue
RDF Query Language: RQLQuerying Large RDF SchemasFiltering/Navigating Complex RDF
descriptions Storing Voluminous RDF descriptions
Alternative DB representationsPerformance Figures
The ICS-FORTH RDFSuite Conclusions and remaining issues
Christophides Vassilis
25
ICS-FORTH London 25/01/02
The Data Independence Issue
Conceptual Level: Describing resources
using one or several RDF schemas
Logical Level: How RDF descriptions
and schemas are physically stored
Logical-schema: Data organization
using tables, objects, etc.
Physical-schema: Data organization
using files, records, indices, etc.
RDF data independence is crucial for
ensuring scalability of real-scale
Semantic Web applications
Christophides Vassilis
26
ICS-FORTH London 25/01/02
The Query Language Issue
Querying the
Structure(Squish)
Querying the
Semantics(RQL)
Querying the
Syntax(XQuery)XML
Repository
Find description elements whose attribute value contains ….
Triple Database
Find statements whose subject is … and object is …
Description Graphs
Find resources classified under … whose property value is ….
Christophides Vassilis
27
ICS-FORTH London 25/01/02
Why a Data Model for RDF ?
As support for physical/logical independenceRDF can be stored in files, a native repository, a relational databaseRDF can be virtual, as a view of a repository, integrated sourcesRDF can be in memory, using data structures in C, C++, Java, etcRDF can be streamed between processes
To describe information content of RDF Statementsto agree and reason about information content, preservation
To define semantics of a data manipulation language: A query language describes in a declarative fashion, the mapping
between an input instance of the data model to an output instance of the data model
Christophides Vassilis
28
ICS-FORTH London 25/01/02
<rdf:Description rdf:ID=“picasso132" fname=Pablo lname=Picasso> <paints rdf:resource="http://museoreinasofia.mcu.es/guernica.gif"/> <paints rdf:resource="http://www.artchive.com/woman.jpg”/> <rdf:type>Painter</rdf:type></rdf:Description> <rdf:Description rdf:about ="http://museoreinasofia.mcu.es/guernica.gif"> <rdf:type>Painting</rdf:type> <created>1937</created> </rdf:Description> <rdf:Description rdf:about =" http://www.artchive.com/woman.jpg"> <rdf:type>Painting</rdf:type> <created>1904</created> </rdf:Description>
<Painter rdf:ID=“picasso132"> <fname>Pablo</fname> <lname>Picasso</lname> <paints> <Painting rdf:about="http://www.artchive.com/woman.jpg”/> <created>1904</created> </paints> <paints> <Painting rdf:about="http://museoreinasofia.mcu.es/guernica.gif"> <created>1937</created> </Painting> </paints></Painter>
But RDF has specifics: Serialization syntax
&r3
&r2paints
&r6
fname
lnamepaints
“Pablo”
“Picasso” 1904created
1937created
r2: museoreinasofia.mcu.es/guernica.jpgr3:www.artchive.com/woman.jpg
r6: picasso132
PaintingPainter
rdf:type rdf:type
XML attributes vs elements for RDF properties fname, lname
XML flat vs nested structures of RDF statements Description vs. Painter elements
RDF properties are unordered, optional, and multivalued 2 paints and 0 creates
One more motivation for a data model :isolate the user from syntactic aspects of RDF/XML
Christophides Vassilis
29
ICS-FORTH London 25/01/02
<rdfs:Class rdf:ID="Artist"/><rdfs:Class rdf:ID="Artifact"/> <rdfs:subClassOf rdf:resource="#Artist"/> </rdfs:Class><rdfs:Class rdf:ID="Painter"> <rdfs:subClassOf rdf:resource="#Artist"/> </rdfs:Class><rdfs:Class rdf:ID="Painting"> <rdfs:subClassOf rdf:resource="#Artifact"/> </rdfs:Class><rdf:Property rdf:ID="fname"> <rdfs:domain rdf:resource="#Painting"/> <rdfs:range rdf:resource=“ http://www.w3.org/rdf- datatypes.xsd#String"/></rdf:Property>
<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="created"> <rdfs:domain rdf:resource="#Painting"/> <rdfs:range rdf:resource=“ http://www.w3.org/rdf- datatypes.xsd#Date"/></rdf:Property>
Distinguish between labels of nodes and edges Painter vs. paints
Class and properties are organized in subsumption hierarchiesPainter <= Artist
Properties are inherited&r6 may also have a creates property
References are typed&r2 should be of class <= Painting
Literal values are typed1937 is not a string but a date value !
But RDF has specifics: Schema Semantics
ArtistString
Artifact
Painting
createsfname
lname
paints
String
createdDatePainter
Christophides Vassilis
30
ICS-FORTH London 25/01/02
But RDF has specifics: Superimposed Descriptions
Resources may belong to multiple (unrelated though isa) classes &r2 is both a Painting and an ExtResource
Heterogeneous descriptions reminiscent of SGML exceptions What is the structure of Painting resources?
&r3
&r2paints
&r6
fname
lnamepaints
“Pablo”
“Picasso”
1904created
1937created
rdf:type rdf:type
ExtResourcefile_size
title String
Int
ArtistString
Artifact
Painting
createsfname
lname
paints
String
createdDatePainter
rdf:type
“Guernica”
4
title
file_size
Christophides Vassilis
31
ICS-FORTH London 25/01/02
RDF/S vs. Well-Known Formalisms
Relational or Object Database Models (ODMG, SQL) Classes don’t define table or object types Instances may have associated quite different properties Collections with heterogeneous members
Semistructured or XML Data Models (OEM, UnQL, YAT, XML Schema) Labels only on nodes or edges Class and property subsumption is not captured Heterogeneous structures reminiscent to SGML exceptions
Knowledge Representation Languages (Telos, DL, F-Logic) Absence of complex values and n-ary relationships (bags, sequences)
Christophides Vassilis
32
ICS-FORTH London 25/01/02
A Semistructured Data Model for RDF
Graph based, unordered, edge/node-labeled (in the style of OEM) But what about sequences (ordered)?
&r2
paints
&r6
fname lname paints
“Pablo” “Picasso”
1904
created
1937
created
“Guernica”4
titlefile_size&r3
Painter
PaintingExtresource
PaintingExtresourceString String
Date DateInt String
friends
&seq1
&r10
1 2fname lname
“XXXX” “YYYY”String String
Painter
Seq
Christophides Vassilis
33
ICS-FORTH London 25/01/02
Towards a Formal Data Model for RDF
An RDF schema is a 5-tuple: RS = (VS, ES, H, , )VS a set of nodesES a set of edgesΗ = (Ν,<) a well-formed hierarchy of names an incidence function: Es VsVs
a labeling function: VS ES Ν Τ An RDF description base, instance of a schema RS, is a 5-tuple: RD =
(VD, ED, , , )VD a set of nodesED a set of edges an incidence function: ED VDVD a valuation function: VD V a labeling function: VD ED 2ΝΤ :
u VD, n CT: (u) [[n]] e ED [u,u’], p
Christophides Vassilis
34
ICS-FORTH London 25/01/02
Why a Type System for RDF ?
For error detection & safety: to verify that statements comply to what the application expectsto make sure that the application accesses valid statements to enforce safe operations (e.g., don’t do float arithmetic on classes!)to check that compositions of operations make sense
For performance:to design storage (saving space, improving clustering, etc.)to process queries (algebraic laws, rewriting path expressions, etc.)
We need a full-fledged Data Definition Language for RDF !RDF Schema is viewed more as an ontology & modeling tool
Christophides Vassilis
35
ICS-FORTH London 25/01/02
Towards a Type System for RDF
Type System:
= L | U | {} | [] | (1: + 2: + … + n:)
Interpretation Function:Literal types, [[ L ]] = dom(L)
Bag types, [[ {} ]] = {1, 2,…, n}, 1, 2,…, n V are values of type Seq types, [[ [] ]] = {1, 2,…, n}, 1, 2,…, n V are values of type Alt types, [[ (1:1 + 2:2 +…+ n:n ) ]] = I, i V, 1<i<n is a value of type i
c C, [[c]] = { | (c)}{(c’) | c’ < c}
p P, [[p]] = {[1, 2] | 1 [[domain(p)]], 2 [[range(p)]]}{(p’) | p’ < p}
Christophides Vassilis
39
ICS-FORTH London 25/01/02
Querying RDF Descriptions: An Introduction to RQL
Christophides Vassilis
40
ICS-FORTH London 25/01/02
The RDF Query Language (RQL)
Declarative query language for RDF description basesrelies on a typed data model (literal & container types + union types)follows a functional approach (basic queries and filters)adapts the functionality of XML query languages to RDF, but also:
treats properties as self-existent individualsexploits taxonomies of node and edge labels allows querying of schemas as semistructured data
Relational interpretation of schemas & resource descriptionsClasses (unary relations)Properties (binary relations)Containers (n-ary relations)
Christophides Vassilis
41
ICS-FORTH London 25/01/02
A Cultural Community Resource Description Example
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
StringMuseum
exhibited
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
Christophides Vassilis
42
ICS-FORTH London 25/01/02
Querying Large RDF Schemas with RQL
Basic Class Queriestopclasssubclassof(Artist)subclassof^(Artist)superclassof(Painter)superclassof^(Painter)
Basic Property Queriestoppropertysubpropertyof(creates)subpropertyof^(creates)superpropertyof(paints)superpropertyof^(paints)domain(creates)range(creates)
Querying the RDF/S meta-schemaClassPropertyLiteral
Christophides Vassilis
43
ICS-FORTH London 25/01/02
Class & Property Querying
Which classes can appear as domain and range of property creates select $X, $Y from {:$X}creates{:$Y} or
select X, Y from Class{X}, Class{Y}, {:X}creates{:Y}
Find all properties defined on class Painting and its superclasses
select @P, range(@P) from {:Painting}@P orselect P, range(P) from Property{P} where domain(P)>=Painting
Find the domain and range of the property creates
seq ( domain(creates), range(creates) ) while thanks to functional composition we can express
subclassof ( seq ( domain(creates), range(creates) ) [0] ) or select X from subclassof(seq(domain(creates), range(creates))[0]) {X}
Christophides Vassilis
44
ICS-FORTH London 25/01/02
Schema Navigation using RQL
Iterate over the subclasses of class Artist
select $X from Artist{:$X} or select X from subclassof(Artist){X}
Find the ranges of the property exhibited which can be reached from a class in the range of property creates
select $Y, $Z from creates{:$Y}.exhibited{:$Z}
Find the properties that can be reached from a range class of property creates, as well as, their respective ranges
select * from creates{:$Y}.@P{:$$Z} orfrom Class{Y}, (Class union Literal){Z}, creates{:Y}.@P{:Z}
Christophides Vassilis
45
ICS-FORTH London 25/01/02
Exporting Schemas using RQL Queries
Find Leaf Classes (i.e., classes without subclasses)
select C1 from Class{C1} where not ( C1 in (select C1 from Class{C2} where C2 < C1) )
Find all schema information (i.e., group related superclasses and properties for each class)
select C, superclassof^(C), (select P, range(P) from Property{P} where domain(P) = C) from Class{C}
Christophides Vassilis
46
ICS-FORTH London 25/01/02
Querying Complex RDF Descriptions with RQL
Find all resources Resource
Find the resources in the extent of the property creates creates or
select * from {X}creates{Y}
Find the resources of type ExtResource and Sculpture ExtResource intersect Sculpture
ExtResource minus SculptureExtResource union Sculpture
Christophides Vassilis
47
ICS-FORTH London 25/01/02
Navigating in Description Graphs using RQL
Find the Museum resources that have been modified after year 2000 (i.e., data path with node and edge labels)
select X from Museum{X}.last_modified{Y} where Y >= 2000-01-01
Find the resources that have been created and their respective titles (i.e., data path using only edge labels)
select X, Z from creates{Y}.title{Z}
Find the titles of exhibited resources that have been created by a Sculptor (i.e., multiple data paths)
select Z, W from Sculptor.creates{Y}.exhibited{Z}, {Z}title{W}
Christophides Vassilis
48
ICS-FORTH London 25/01/02
Using Schema to Filter Resource Descriptions
Find the Painting resources that have been exhibited as well as the related target resources of type ExtResource (i.e., restrict multiply classified property target values using node labels)
select X, Y from {X:Painting}exhibited{Y}.ExtResource
Note the difference with the following path exression
select X, Y from {X:Painting}exhibited{Y:ExtResource}
Find modified resources which can be reached by a property applied to the class Painting and its subclasses (i.e., restrict property source values using edge labels)
select @P, Y, Z
from {:$X}@P.{Y}last_modified{Z}
where $X <=Painting
Christophides Vassilis
49
ICS-FORTH London 25/01/02
Discover the Schema of RDF Descriptions
Find the description of a resource with URI “http://www.museum.es”select $X, (select @P, Y from {Z : $Z} @P {Y} where X = Z and $X = $Z)from $X {X} where X = &http://www.museum.es Find the descriptions of resources whose URI match “www.museum.es”select X, (select $W, (select @P, Y from {Z : $Z} @P {Y} where W = Z and $W = $Z) from $W {W} where W = X) from Resource {X} where X like "*www.museum.es*"
Christophides Vassilis
50
ICS-FORTH London 25/01/02
And if you still like triples …
Find the description of resources which are not of type ExtResource
( (select X, @P, Y from {X} @P {Y}) union (select X, type, $X from $X {X}))minus( (select X, @P, Y from {X:ExtResource}@P{Y}) union (select X, type, ExtResource from ExtResource {X}))
Christophides Vassilis
56
ICS-FORTH London 25/01/02
Storing RDF Descriptions: RSSDB Preliminary Performance Results
Christophides Vassilis
57
ICS-FORTH London 25/01/02
Modeling the ODP Catalog with RDF/S
Class related
ns1: http://www.dmoz.org/topic.rdf
rdf: http://www.w3.org/1999/02/22-rdf-syntax-ns#rdfs: http://www.w3.org/2000/01/rdf-schema# typeOf(instance)
subClassOf(isA)attribution
Regional Recreation
Lodging
Vacation-Rentals
related
ns2: www.oclc.org/dublincore.rdfs
Ext.Resource
stringtitle
description
string
date
file_size
last_modifiedIle-de-France
Paris
Travel
Hotel Directories
Hotel
&r1 &r3&r2 &r4
title title title
Notre-Dame
HotelSiteofficielde DisneylandParis
Disneyland
Officialsiteof DisneylandParis
title
description description
Danube OrsaySunScale
&r1: http://www.sunscale.com/france/paris/index.htm
Christophides Vassilis
58
ICS-FORTH London 25/01/02
ODP Statistics
ODP Version: 16-01-2001
170 Mbytes of class hierarchies
700 Mbytes of resource descriptions
337,085 topics
16 hierarchies with
max depth: 13 ( 6.86 on average)
max # subclasses: 314 ( 4.02 on average)
2,342,978 URIs
Christophides Vassilis
59
ICS-FORTH London 25/01/02
Generic Representation
id: int1
uri: texthttp://www.dmoz.org/topics.rdfs#Hotel
Resources
3 http://www.oclc.org/dublincore.rdfs#title2 http://www.dmoz.org/topics.rdfs#Hotel Directories
9 r1
4 http://www.dmoz.org/schema.rdf#Ext.Resource
predid: int6
Triplessubid: int
2objid: int
15 3 75 1 8
objvalue: text
5 http://www.w3.org/1999/02/22-rdf-syntax-ns#type6 http://www.w3.org/2000/01/rdf-schema#subClassOf
7 http://www.w3.org/1999/02/22-rdf-syntax-ns#Property
5 9 2
8 http://www.w3.org/2000/01/rdf-schema#Class
3 9 SunScale
Christophides Vassilis
60
ICS-FORTH London 25/01/02
Specific Representation
subid: int11
13
SubClass superid: int
1
12
subid: int16
SubPropertysuperid: int
1412 1
Namespace
Type
id: int11
rangeid: int4412
13
id:int1
uri: texthttp://www.w3.org/2000/01/rdf-schema#
3 http://www.oclc.org/dublincore.rdfs#4 http://www.dmoz.org/topics.rdfs#
id: int1
nsid: int1
lpart: textResource
2 2 Bag2 http://www.w3.org/1999/02/22-rdf-syntax-ns#3 2 Seq4 String
Classnsid: int
5lpart: text
Ext.Resource 1415
Propertynsid: int
33
lpart: texttitledescription
domainid: int114 Hotel
4 Hotel Directories
id: int
16 5 title 11 4
subtable
t12
URI: textt1
source: textt15
target: text
URI: textr1
t11URI: text
r2
URI: textr1
t13r2
source: text target: text
source: textr1
t14target: text
SunScaler2 Pulitzer Opera
t16
classid: int11
1311
uri: textr1
r1
Instances
r2
r2 12
Christophides Vassilis
61
ICS-FORTH London 25/01/02
DBMS Size vs. Schema Triples
DBMS size scales linearly with the number of schema triples
SpecRepr GenRepr
Aver. triple size (with indexes)
0.086 KB (0.1734 KB)
0.1582 KB (0.3062 KB )
Aver. triple storage time (with indexes)
0.0021 sec (0.0025) sec
0.0025 sec (0.0032 sec)
Christophides Vassilis
62
ICS-FORTH London 25/01/02
DBMS Size vs. Data Triples
DBMS size scales linearly with the number of data triples
SpecRepr GenRepr
Aver. triple size (with indexes)
0.123 KB (0.2566 KB)
0.123 KB (0.2706 KB )
Aver. triple storage time (with indexes)
0.0033 sec (0.0043) sec
0.0039 sec (0.00457 sec)
Christophides Vassilis
63
ICS-FORTH London 25/01/02
Query Templates for RDF description bases
Pure schema queries
Q1 Find the range (or domain) of a property
Q2 Find the direct subclasses of a class
Q3 Find the transitive subclasses of a class
Q4 Check if a class is a subclass of another class
Queries on resource descriptions using available schema knowledge
Q5 Find the direct extent of a class (or property)
Q6 Find the transitive extent of a class (or property)
Q7 Find if a resource is an instance of a class
Q8 Find the resources having a property with a specific (or range of) value(s)
Q9 Find the instances of a class having a given property
Schema queries for specific resource descriptions
Q10 Find the properties of a resource and their values
Q11 Find the classes under which a resource is classified
Christophides Vassilis
64
ICS-FORTH London 25/01/02
Execution Time of RDF Benchmark Queries
Christophides Vassilis
65
ICS-FORTH London 25/01/02
Comparison
Specific Representation permits the customization of the database representation of RDF metadata
Specific Representation outperforms the Generic Representation for all types of queries
Q1, Q2, Q5, Q7, Q10, Q11: by a factor up to 3.73Q3, Q4, Q6: by a factor up to 2.8Q8, Q9: by a factor up to 95,538
Generic representation pays severe penalty for maintaining large tables (Triples, Resources)
e.g., queries Q8, Q9 require (self-) joins of Triples, Resources
Christophides Vassilis
66
ICS-FORTH London 25/01/02
Other Issues
RDF Metadata Generation from Legacy Repositories:need to capture schemas from heterogeneous resources
RDF Schema Evolution and Metadata Revision: to support the dynamics of resource descriptions
RDF Repositories Distribution:for integration with WebDAV or LDAP-like architectures
RDF Query Languages Optimization:for real-scale Semantic Web applications
Christophides Vassilis
67
ICS-FORTH London 25/01/02
The ICS-FORTH R&D Activities on the Semantic Web
Christophides Vassilis
68
ICS-FORTH London 25/01/02
The C-Web Project
EC IST Project (13479) 1999-2000 Overall Aim: Set-up methodologies and
infrastructure for fast deployment and easy management of Web Portals for communities requiringeffective knowledge
assimilation,elicitationefficient query answering
Partners: INRIA(FR), FORTH(GR), EDW(IT)
Running Application Scenario: Learning
Portals for intranets or the InternetCorporate Knowledge Servers (e.g.,
automobile, telecommunications)Memory Organizations (e.g., museums,
libraries, archives)
Christophides Vassilis
69
ICS-FORTH London 25/01/02
Project “MESMUSES”Programme:(IST) KAIII.1.4. Multimedia
Content and Tools (Access to digital collections of cultural and scientific content)
Contract: IST-2000-26074 (02/2001 – 07/2003)
Partners: INRIA (France),
FINSIEL - Multimedia Services (Italy),
ICS-FORTH (Hellas),
ENSTB - Ecole Nationale Supérieure des Télécommunications - Bretagne (France), VALORIS - Group, Paris (France)
IMSS - Istituto e Museo di Storia della Scienza, Firenze (Italy)
CSI - Cité des Sciences et de l'Industrie, Paris (France)
EDW International, Milano (Italy) DET-UNIFI - University of Florence (Italy)
Christophides Vassilis
88
ICS-FORTH London 25/01/02
Christophides Vassilis
89
ICS-FORTH London 25/01/02
University Portals
Most of the Corporate Portal features apply to higher educationuPortal is bridging the gap between corporate portals and the
needs of Higher Education Institutions One of the most complex portal applications is instruction. Several
information channels have to be synchronized together to:present learning materials and assessmentsmonitor the learner’s progress and adapt the presentation to the
learner’s knowledgeaudit the progression through contentand perhaps even simulate a process
Christophides Vassilis
90
ICS-FORTH London 25/01/02
The Evolving Campus
Christophides Vassilis
91
ICS-FORTH London 25/01/02
The 21Century Campus in the .com World
Christophides Vassilis
92
ICS-FORTH London 25/01/02
The Higher Education Web World
Christophides Vassilis
93
ICS-FORTH London 25/01/02
uPortal Hierarchy
Christophides Vassilis
94
ICS-FORTH London 25/01/02
uPortal Interfaces
AuthenticationProving your identity
AuthorizationDeciding what you can access
Directory servicesSuch as populating
EduPerson User preferences
Profiles, structure, themes, skins
Channel informationAvailability and configuration