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Z39.50, RDF and the Web PowerPoint PPT Presentation

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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Z39 50 rdf and the web l.jpg

Z39.50, RDF and the Web

ZIG Tutorial August 1999

Poul Henrik Jørgensen,

Danish Library Centre, www.dbc.dk


Contents l.jpg

Contents

  • WWW Benefits and Limitations

  • Z39.50 Benefits and Limitations

  • Resource Description Framework, RDF

Z39.50 & Web / DBC-PHJ


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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


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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


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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


Web search example l.jpg

Web Search Example

Z39.50 & Web / DBC-PHJ


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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


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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


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Z39.50 Architecture

Z-Server front-end

Search & Retrieve

User interface

Z-Client back-end

Z39.50

Data-base

Z39.50 & Web / DBC-PHJ


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Z39.50 Example

Z39.50 & Web / DBC-PHJ


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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


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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


Rdf overview l.jpg

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


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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


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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


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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


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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


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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


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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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