Declarative Languages for Querying Portal Catalogs

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1 Declarative Languages for Querying Portal Catalogs V. Christophides D. Plexousakis G. Karvounarakis S. Alexaki Computer Science Department, University of Crete Institute for Computer Science - FORTH Heraklion, Crete 1 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, ubiquitous comprehensive, and integrated access to various information resources gweb Portals Workplace Commerce C-Web Education Health 2 1 1

2 Portals Classification Existing Communities On-line Communities 3 Portals Classification 4 2 2

Knowledge Processes in Corporate Communities Generating new knowledge Accessing knowledge from external sources Representing knowledge in documents and databases Embedding knowledge in services and

3 Knowledge Processes in Corporate Communities Generating new knowledge Accessing knowledge from external sources Representing knowledge in documents and databases Embedding knowledge in services and processes Dissemination of knowledge within organisation Using knowledge in decision making 5 Community Web Portals: Main Features Advanced Knowledge Schemas (ontologies, thesauri) Heterogeneous resource descriptions <tag1> <tag1> <tag2> <tag2> <tag3> <tag3> </tag1> </tag1> Complexity and diversity of information resources 6 3 3

4 What we need? n Flexible Modeling of Community Web Portal Catalogs ❶ Exploit existing forms of community knowledge Ranging from simple vocabularies to formal ontologies ❷ Describe in various ways community information resources Administration, Classification, Content Rating, Channels,. n Secondary Storage Management of Portal Metadata ❶ Large Schemas: e.g., 100 Mbytes of ODP Topics (the Art Hierarchy contains terms) ❷ Voluminous Description Bases: e.g., 700 Mbytes of ODP indexed URLs n Declarative Query Languages for Portal Catalogs ❶ Interleave schema with data querying ❷ Optimize access to Portal Catalogs 7 Our Approach RDF Virtual XML Warehouse High-level Access to community information Documents Databases Archives Web Use W3C Standards to describe (RDF/S) & exchange (XML) information Our Contribution: Declarative Languages for Browsing & Querying 8 4 4

5 Outline n Example of a Portal Catalog for Cultural Communities n Describing and Querying Community Resources ga Formal Data Model for RDF/S gthe RDF Query Language (RQL) n Architecture gcore Middleware (RDF Store, Parser/Loader, Query Interpreter) n Build Community Web Portals gcreate/extract Resource Metadata gdevelop Specific Applications for Communities goptimize RDF Storage and Queries n Summary 9 Building a Cultural Community Web Portal using RDF String String Portal Schema fname lname Sculptor Artist Painter sculpts creates paints Artifact Painting exhibited Museum Sculpture technique String Date String last_modified title ExtResource Portal Resource Descriptions r2: museoreinasofia.mcu.es/ guernica.jpg Web Resources Rodin Pablo Picasso lname fname &r5 lname &r6 creates paints paints r1: thinker.gif &r1 &r2 exhibited technique last_modified &r3 &r4 last_modified title oil on canvas 2000/01/02 r3: woman.jpg 2000/06/09 Reina Sofia Museum r4:museoreinasofia.mcu.es

6 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 syntax n RDF Schema (RDFS): Schema Vocabularies gspecialization of both classes & properties (simple & multiple) gmultiple classification under several classes gunordered, optional, and multi-valued properties gdomain and range polymorphism of properties 11 RDF/XML Serialization: Data <rdf:rdf xml:lang="en" xmlns:rdf=" xmlns:rdfs=" xmlns="">. <Painter rdf:id= picasso132"> <fname>pablo</fname> <lname>picasso</lname> <paints> <Painting rdf:about=" <exhibited> <Museum rdf:about=" </exhibited > <technique>oil on canvas</technique> </Painting> </paints> <paints> <Painting rdf:about=" /> </paints> </Painter> <ExtResource rdf:about=" <title>reinasophia Museum</title > <lastmodified>2000/06/09</lastmodified> <Sculptor rdf:id="rodin424" lname="rodin > <creates> <Sculpture rdf:about=" </creates> </Sculptor> </rdf:rdf>

7 RDF/XML Serialization: Schema <rdf:rdf xml:lang="en" xmlns:rdf=" 22-rdf-syntax-ns#" xmlns:rdfs=" PR-rdf-schema #"> <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=" TR/1999/PR-rdf-schema #Literal"/> </rdf:property> <rdf:property rdf:id="title"> <rdfs:domain rdf:resource="#extresource"/> <rdfs:range rdf:resource= " TR/1999/PR-rdf-schema #Literal"/> </rdf:property>. </rdf:rdf> 13 RDF/S vs. Well-Known Formalisms n Relational or Object Database Models (ODMG, SQL) g Classes don t define table or object types g Instances may have associated quite different properties g Collections with heterogeneous members n Semistructured or XML Data Models ( ÏÅÌ, UnQL, YAT, XML Schema) g Labels only on nodes or edges g Class and property subsumption is not captured g 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

8 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 gp 1,p 2 P and p 1 < p 2 => domain(p 1 ) domain(p 2 ) and range(p 1 ) range(p 2 ) n Type System: τ = τ L τ U {τ} [τ] (1:τ + 2:τ + + n:τ) n Interpretation Function: gliteral types, [[ τ L ]] = dom(τ L ) gbag types, [[ {τ} ]] = {ν 1, ν 2,, ν n }, ν 1, ν 2,, ν n V are values of type τ gseq types, [[ [τ] ]] = {ν 1, ν 2,, ν n }, ν 1, ν 2,, ν n V are values of type τ galt types, [[ (1:τ 1 + 2:τ n:τ n ) ]] = ν I, ν i V, 1<i<n is a value of type τ i gc C, [[c]] = {ν ν π(c)} {π(c ) c < c} gp P, [[p]] = {[ν 1, ν 2 ] ν 1 [[domain(p)]], ν 1 [[range(p)]]} {π(p ) p < p} 15 A Formal Data Model for RDF n An RDF schema is a 5-tuple: RS = (V S, E S, H, ψ, λ) gv S a set of nodes ge S a set of edges gç = (Í,<) a well-formed hierarchy of names gλ a labeling function: V S E S Í Ô gψ an incidence function: E s V s V s n An RDF description base, instance of a schema RS, is a 5-tuple: RD = (V D, E D, ψ, ν, λ) gv D a set of nodes ge D a set of edges gψ an incidence function: E D V D V D gν a valuation function: V D V gλ a labeling function: V D E D 2 Í Ô : u V D, λ n C T: ν(u) [[n]] e E D [u,u ], λ p

9 A Formal Data Model for RDF H < Class Property < [[. ]] val n literals l t L t C t P n p U URI y resources l [[. ]] {[val,val}] t {} t [] n container N T V S 17 The RDF Query Language n Declarative query language for RDF description bases grelies 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 descriptions gclasses (unary relations) gproperties (binary relations) gcontainers (n-ary relations)

10 Browsing Portal Catalogs with RQL n Simple set queries on class and property extents: gfind the resources in the extent of the property creates creates Includes paints & sculpts {{ [ [ museoreinasofia.mcu.es/guernica.gif], [ }} gfind the resources of type painter and sculptor ExtResource intersect Sculpture {{ }} Multiply classified resources 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 19 Personalizing Portal Catalogs with RQL n Navigational queries on semistructured resource descriptions gfind the Museum resources that have been modified in year select x from Museum{x}.last_modified{y} where y >= 2000/01/01 Data paths not {{museoreinasofia.mcu.es}} foreseen in the schema 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

11 Querying Portal Catalogs with Large Schemas n Filtering both resource descriptions and schemas gfind the paintings having as technique oil on canvas that have been created by a neo-impressionist painter Schema Filtering on Class hierarchies Data filtering with schema information select y from {:$X}creates{y:Painting}.technique{z} where $X <= neo-impressionist and z = oil on canvas 21 Querying Portal Schemas with RQL n Pure schema queries gfind the properties which specialize the property creates and may have as domain the class Painter along with their corresponding range classes $Y from {:Painter}@P{:$Y} <= creates All Properties defined or inherited in class Painter {{ [creates, Artifact], [creates, Painting], [creates, Sculpture], [paints, Painting] }} Schema filtering on property hierarchies

12 RQL: Examples String String ns1#fname ns1#creates ns1#has_style ns1#artistns1#creates ns1#createsns1#artifact ns1#style ns1#lname ns1#has_material ns1#creates ns1#painterns1#sculptor ns1#painting ns1#sculpture String dc#last_modified ns1#paints ns1#sculpts odp#extpage Date ns1#impressionist ns1#postimpressionist h Similar functionality to DBMS schema QLs (SchemaSQL, XSQL) Useful for large schemas (integrating ontologies and thesauri) 23 Putting it all Together n Nested schema and data queries gfind the resources modified after 2000/01/01 which can be reached by a property applied to the class Painting and its subclasses select R, y from from {:$X}@P where $X <= Painting){R}.{y}last_modified{z} where z >= 2000/01/01 {{ [exhibited, museoreinasofia.mcu.es] }} R ranges over the labels of type property n Subcommunities may use different schemas while sharing the same description base

13 RQL:Examples Portal Schema Museum exhibited technique Painting String &r2 exhibited technique &r4 last_modified oil on canvas 2000/06/09 Portal Resource Descriptions last_modified &r3 2000/01/02 25 n Schema and data queries Putting it all Together gfind all metadata about the resources of the site museoreinasofia.mcu.es select x,$$y,$p,z,$$w URLs pattern matching from {x:$$y}$p{z:$$w} where x like *museoreinasofia.mcu.es* or y like *museoreinasofia.mcu.es* {{[ 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

14 The Core Portal Middleware ICS-VRP Parser Validator VRP Internal RDF Model RDF Loader Loading RDF Java APIs JDBC SQL3 Class c_name Artist subcl Painter Artist URI creates ORDBMS Property domainp_name range Artist creates Artifact SubClass SubProperty supcl Artist subpr suppr paints creates creates source target paints creates SQL3+ SPI functions LIB C++ SQL3 DBMS RDF query API ICS-RQL Interpreter Typing Evaluation Graph Constructor Parser 27 The ICS-FORTH R&D Activities 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

15 Architecture of Community Web Portals Schema Generator Artist Painting Painter RDF/XML Schema Museum Query Browsing Interface RQL XML/XSL CWEB/Application Server Artist URL http RDF/XML Descriptions Resource Description Interface Middleware APIs Client Tier Metadata Store RDF/XML Loader Session Manager Query Engine URL Resolver XML/XSL Processor Logical Middle Tier http XML XML XML XML Wrapper Resources XML enabled DBMS Well-formed XML docs on the Web Other docs on the Intranet e.g. mails, news, reports 29 Describing Community Information Resources Semantics Metadata Type Resources Nature Content Descriptive (unstructured, semistructured, structured) Individual Manual Static Automatic Collection Dynamic Query Mediation Syntax Structure Descriptive (semistructured, structured) Manual Manual Manual System Management (all kinds) Automatic Automatic Automatic

16 Related Work n Information Integration Systems g YAT (INRIA Verso) www-rocq.inria.fr/~simeon/yat g MIX (San Diego) g TSIMMIS (Stanford) www-db.stanford.edu/tsimmis g GARLIC (IBM) g DISCO (INRIA Caravel) rodin.inria.fr/eprototype_disco.html g DIOM (Alberta, Canada) ugweb.cs.ualberta.ca/~diom g Nomenclator (Bell Labs) cm.bell-labs.com/cm/cs/what/nomenclator g MANIFOLD (AT&T) g Picsel (ORSAY) g CoBase (California) cobase- g Momis (Modena, Italy) sparc20.dsi.unimo.it/momis g InfoHarness & InfoQuilt (Georgia) lsdis.cs.uga.edu/proj/proj.html g Infomaster (Stanford) infomaster.stanford.edu/infomaster-info.html g InfoSleuth (MCC,Texas) g Ariadne (Southern California) g SIMS (Southern California) g HERMES (Maryland, College Park) g Carnot (MCC,Texas) n Main Focus on structured and semi-structured data integration 31 Related Work n Ontology-based Information Systems gon-to-knowledge (IST ) gibrow (IST ) gontoseek (Padova, Italy) gobserver (Basque Country, Spain) siul02.si.ehu.es/~jirgbdat/observer gontological Mediation (New York at Buffalo) n Main Focus on knowledge integration n Ontology-driven Document Annotation Systems gontobroker (Karlsruhe, Germany) ontobroker.aifb.uni-karlsruhe.de gshoe (Maryland, College Park) gwebkb (Griffith, Australia) meganesia.int.gu.edu.au/~phmartin/webkb gohtml, XAL n Main Focus on intelligent document access

17 Related Work n Corporate Knowledge Management and Ontological Engineering gcommonkads (ESPRIT P5248) gcyc (MCC,Texas) gtove (Toronto) www. eil.utoronto.ca/eil.html genterprise (DTI, ISIP Programme) gkactus (ESPRIT Project 8145) gkraft (Liverpool, U.K.) go-plan (Edinburgh, U.K.) www. aiai.ed.ac.uk/~oplan ggeneralized Upper Model (GMD) 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 33 Related Work n Digital Libraries gelectronic Environmental DL (Berkeley) elib.cs.berkeley.edu ginformedia (Carnegie-Mellon) ginterspace (Illinois) dli.grainger.uiuc.edu gumdl (Michigan) gdl Technologies (Stanford) www-diglib.stanford.edu galexandria (Santa Barbara) alexandria.sdc.ucsb.edu gadept (Georgia) lsdis.cs.uga.edu/~adept gercim DELOS DL (Europe) gukoln (U.K.) gcidl (Canada) gwaikato (New Zealand) nzdlbeta/gw n Main Focus on system infrastructure for global information sharing

18 Summary and Future Work n Our contribution: gfirst declarative language for uniformly querying RDF schemas and resource descriptions gformal model for RDF/S (+ typed, operational semantics) n Functionality evaluation: gdeveloped in the context of the EC project C-Web ( gaccepted for use in the ongoing EC projects: MesMuses ( Ontoknowledge ( 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)

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