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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


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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


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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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