1. 1 ICS-FORTH & Univ. of Crete Paris January 2000 Community Webs (C-Web): Functionality and Architecture Issues V. Christophides Computer Science Department, University of Crete Institute for Computer Science - FORTH Heraklion, Crete

2. 2 ICS-FORTH & Univ. of Crete Paris January 2000 What is C-Web ? l Set-up methodologies and infrastructure for fast deployment and easy management of knowledge-intensive Web applications in communities requiring: u effective knowledge assimilation, elicitation,... u efficient query answering C-Web education health commerce workplace

3. 3 ICS-FORTH & Univ. of Crete Paris January 2000 C-Web Main Idea: Virtual XML Warehouse l Main Goal: to provide a generic platform for describing, organizing and querying various XML resources according to a concept taxonomy shared by a specific community Single Point of Access Files Virtual XML Warehouse Documents Databases Web Knowledge

4. 4 ICS-FORTH & Univ. of Crete Paris January 2000 C-Web Objectives l Reuse existing knowledge structures (e.g. ontologies, thesauri) l Integrate easily heterogeneous XML resources (e.g. data, documents) l Provide an intelligent information access (i.e. conceptual querying and browsing) l Support collaboration facilities & expertise management (e.g. annotations) l Enable automatic generation of new information resources (e.g. e-books)

5. 5 ICS-FORTH & Univ. of Crete Paris January 2000 C-Web Functionality: Current Status l Support for creating community conceptual models u integration of existing ontologies and thesauri u definition different viewpoints l Support for describing and integrating resources u resource content description metadata (CDM) u resource structure mapping metadata (SMM) l Support for conceptual browsing and querying u High level property-centric queries to resources u Querying both conceptual schemata and related instances l Support for collaborative resource annotation l Support for intelligent information publishing

6. 6 ICS-FORTH & Univ. of Crete Paris January 2000 The main C-Web Requirement: Interoperability l Heterogeneity is not a drawback, but a feature of autonomous information resources in large scale distributed systems  Interoperability : the ability to uniformly share, interpret and manipulate data and documents from heterogeneous resources domain & data models vocabularies communication protocols transaction processing security policies data formats abstraction & aggregation details Semantic Structure Functional System Syntactic viewpoints contexts query language dialects

7. 7 ICS-FORTH & Univ. of Crete Paris January 2000 Sculptor Artist Artifact Museum Painter Sculpture Painting Fine-ArtArcheological Impressionism Neo-Impressionism Pointillism BT Conceptual Logical Physical C-Web Design Principle: Repository Independence Source 1: XML enabled DBMS XML SQL XSQL Servlet Source 2: XML Repository <!ATTLIST MusArtifact material CDATA #IMPLIED size CDATA#IMPLIED>... XQL Xpath Servlet Domain Model <elementTypeRef name=”Creator" minOccur="1"/> ….

8. 8 ICS-FORTH & Univ. of Crete Paris January 2000 W3C C-Web & Related W3C Standards l Semantic Interoperability: Content Description & Metadata Standards u ontologies (e.g. ICOM/CIDOC), thesauri (e.g., ULAN, TGN, AAT), metadata element sets (e.g. CIMI/Aquarelle Z39.50 profile) u Resource Description Framework (RDF) for expressing semantics l Structural Interoperability: Schema languages for specifying logical structure of Web resources u DTDs, XML Schema l Syntactic Interoperability: Markup languages for exchanging (semi-) structured data over the Web u XML, XLL,... l Functional Interoperability: Data Manipulation languages for (semi-) structured data over the Web u XPath, XQL, XSL,...

9. 9 ICS-FORTH & Univ. of Crete Paris January 2000 From RDF Schemata to XML resources RDF schema RDF/XML metadata XML Resources artist:Artist artist:Painter artist:Sculptor s about #August_Rodin artist:lives_in d rdfs:Literal Paris artist:Sculpture d r artist:sculpts r #The Burghers of Calais #The Gates of Hell s s : rdfs:subclassOf t : rdf:type ttt d: rdfs:domainr: rdfs:range artist:lives_in artist::sculpts artist:sculpts artist:material artist:Material Iron artist::material r d www.artist.gr/august_rodin August Rodin Paris The Gates of Hell Iron ……..

10. 10 ICS-FORTH & Univ. of Crete Paris January 2000 XML Resources and C-Web Metadata Artist NameLivesWork TitleMaterialStyle Museum Object Natural Object Artifact isa Period of period has_style Style String Material consists of title C-Web Schema XML Structure August Rodin Paris The Gates of Hell Iron …….. <rdf:RDF xmlns:rdf="...#” xmlns:rdfs="...#" xmlns:s=”mycweb.forth.gr/...#"> … C-Web Resource Description Interface August Rodin Paris The Gates of Hell Iron …….. August Rodin Paris The Gates of Hell Iron ……..

11. 11 ICS-FORTH & Univ. of Crete Paris January 2000 The C-Web Architecture Query Engine Session Manager URL Resolver Metadata Store Painter Museum Painting XML Wrapper Resources XML Logical Middle Tier CWEB/APP Server Other docs news, reports on the Intranet e.g. mails, Well-formed XML docs on the Web XML XML enabled DBMS Client Tier XML/XSLRDF/XML Schema Editor Virtual Document Render RDF/XML Loader XML/XSL Processor Artist URL Resource Description Interface Query Browsing Interface Resource Annotation Interface Artist RDF/XML Middleware APIs http

12. 12 ICS-FORTH & Univ. of Crete Paris January 2000 C-Web Middleware: Main Features ÊGenericity: capture any XML structure (various DTDs), any form of XML semantics (DTDs, XML Schema), any XML access interface/protocol (XQL, XLL) ·Scalability: w.r.t. the volume of XML resources, the number of XML repositories, network and server load, etc. ¸Extensibility: evolution of XML resources semantics and structure does not affect the main processing components and interfaces ¹Openness: rely on standards & APIs allowing to plug and play the same components & services in various applications, domains, etc.

13. 13 ICS-FORTH & Univ. of Crete Paris January 2000 The C-Web Architecture: Pending Issues l Schema Editor: Standalone application or client of the Middleware? u Where are stored large thesauri/ontology before their integration? u Who is responsible for Schema Validation (from scratch vs. integrated)? u What communication protocol we need with the C-Web Middleware? l Resource Description Interface: Loose or Tight coupled with the Middleware? u How C-Web Schema browsing/querying is implemented? u Where we can find the XML DTDs/Schemata of resources? u Who is responsible for Resource Description Validation? u What communication protocol we need with the C-Web Middleware? l Metadata Store: What persistence support we need? u What is an efficient RDF storage model (indexing & clustering)? u Did we also need to support updates/versions (versioning model)? u What are the authentication/security policies (RDF/XML with signatures)? u What is the result form of a C-Web query (triples, statements or objects)?

14. 14 ICS-FORTH & Univ. of Crete Paris January 2000 C-Web Communication Protocol: 3 Alternatives ClientServer ClientServer ClientServer Query Reply Query Handle Next Reply Subscribe Synchronous: a blocking query waits for an expected reply Asynchronous: a nonblocking subscribe results in replies Server maintains state; replies sent individually when requested

15. 15 ICS-FORTH & Univ. of Crete Paris January 2000 Towards a C-Web Physical Architecture Metadata Store CWEB/APP Server Schema Editor Resource Description Interface RDF/XML Parser Loader Metadata Store Metadata Store RDF/XML Query Engine Query Browsing Interface Session Manager NM1 Ontologies NM2 Thesauri NM3 C-Web Schema & Instances Internet Ethernet RDF/XML Schema RDF/XML Descriptions RDF-QL Persistent Namespace Service