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Z39.50, RDF and the Web

Z39.50, RDF and the Web ZIG Tutorial August 1999 Poul Henrik Jørgensen, Danish Library Centre, www.dbc.dk Contents WWW Benefits and Limitations Z39.50 Benefits and Limitations Resource Description Framework, RDF Web Harvesters

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Z39.50, RDF and the Web

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  1. Z39.50, RDF and the Web ZIG Tutorial August 1999 Poul Henrik Jørgensen, Danish Library Centre, www.dbc.dk

  2. Contents • WWW Benefits and Limitations • Z39.50 Benefits and Limitations • Resource Description Framework, RDF Z39.50 & Web / DBC-PHJ

  3. Web Harvesters • Web Harvesters follow links to find HTML documents on selected Web Servers • Fetches documents and extracts words from the text • Meta tags are (sometimes) ignored • Maintains databases of words with URLs of corresponding Web pages Z39.50 & Web / DBC-PHJ

  4. Web Search Overview • Displays search-form in a Web browser • Search-words are submitted to index- database • List of Web pages with hyperlinks is returned to Web browser • User clicks on URLs to fetch original HTML documents from the source Z39.50 & Web / DBC-PHJ

  5. Web Search Architecture Web Har-vester Web Server Source Docu-ments 1. Fetch words 3. Fetch documents Web Index 2. Search index Index Search Web Server Web Browser Z39.50 & Web / DBC-PHJ

  6. Web Search Example Z39.50 & Web / DBC-PHJ

  7. Web Search Benefits and Issues • Utilize standard Web browsers • Returns many URLs to Web pages • Information within databases is ignored • Tied to special search forms • Imprecise search on free-text words • Limited control over presentation formats Z39.50 & Web / DBC-PHJ

  8. Z39.50 Overview • Z39.50 Targets (Z-Servers) share a standard system interface to Z39.50 Origins (Z-Clients) • Z-Clients support specialised user interfaces • Z-Clients submit metadata Search- and Present requests etc. to Z-Servers • Z39.50 search metadata and retrieve information from databases Z39.50 & Web / DBC-PHJ

  9. Z39.50 Architecture Z-Server front-end Search & Retrieve User interface Z-Client back-end Z39.50 Data-base Z39.50 & Web / DBC-PHJ

  10. Z39.50 Example Z39.50 & Web / DBC-PHJ

  11. Z-Web Gateway Architecture Web browser Web front-end Z-Client back-end Z-Server front-end Data-base HTTP Z39.50 Z39.50 & Web / DBC-PHJ

  12. Z39.50 Benefits and Issues • Precise searching with metadata attributes • Z39.50 includes Extended Services to retrieve, order and update information. • Information systems require standard Z-Server front-ends • Require speciel Z-Clients • Standard system interface between Z-Clients and Servers Z39.50 & Web / DBC-PHJ

  13. RDF Overview • Resource Description Framework • Developed by W3C from PICS • General information model based on Directed Labeled Graphs (DLG) – and NIAM • Serilization and Schema based on XML • XML Namespace defines vocabularies • Document Object Model (DOM) as API Z39.50 & Web / DBC-PHJ

  14. RDF Elements • An RDF Resource is an instance of one or more Classes • Resources have Properties • A Class may be a Subclass of another Class • Properties are values or Relations to other Resources • Statements: Resource (Subject) + Property (Predicate) + Value (Object) Z39.50 & Web / DBC-PHJ

  15. RDF Statement • Poul Henrik Jørgensen (Value) • is the creator (Property) • of the resource http://neptun.dbc.dk/efila/documents/zigmar1999/zigmarch1999b.htm (Subject). Ref.: http://www.w3.org/TR/REC-rdf-syntax/ Z39.50 & Web / DBC-PHJ

  16. RDF XML Syntax <?xml version="1.0" ?> -<RDF xmlns=http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:s="http://description.org/schema/"> <Description about= • "http://neptun.dbc.dk/efila/documents/zigmar1999/zigmarch1999b.ht”> <s:Creator>Poul Henrik Jørgensen</s:Creator> </Description> </RDF> Z39.50 & Web / DBC-PHJ

  17. Possible RDF and Z39.50 Synergy • Z39.50 Services • Z39.50/HTTP Profile: • HTTP transmission protocol • XML Transfer Syntax • XML Namespace as search attributes • XSL based Query Language (XQL) Z39.50 & Web / DBC-PHJ

  18. XQL Example <xsl:for-each select = "book[publisher/name = 'Addison-Wesley'] /author"> <xsl:value-of /> </xsl:for-each> http://www.w3.org/TandS/QL/QL98/pp/xql.html Z39.50 & Web / DBC-PHJ

  19. Summary • Web Search engines have two drawbacks: • No standard interface (human or otherwise) • No standard service models • RDF offers general method to describe objects and relationships (i.e. Metadata) • Z39.50/HTTP + XMLNS + RDF + DOM + XQL may be a winning combination Z39.50 & Web / DBC-PHJ

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