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Web Standards. Brian Kelly Email Address UK Web Focus B.Kelly@ukoln.ac.uk UKOLN URL University of Bath http://www.ukoln.ac.uk/. - PowerPoint PPT Presentation
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Web Standards
Brian Kelly Email Address
UK Web Focus B.Kelly@ukoln.ac.uk
UKOLN URL
University of Bath http://www.ukoln.ac.uk/
UKOLN is funded by the British Library Research and Innovation Centre, the Joint Information Systems Committee of the Higher Education Funding Councils, as well as by project funding from the JISC’s Electronic Libraries Programme and the European Union. UKOLN also receives support from the University of Bath where it is based.
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Contents
• Introduction
• Web Standards Overview
• Web Standards:• Data Formats• Transport• Addressing
• Metadata
• Distributed Searching
• Deployment Issues
Aims of Talk• To give brief overview
of web architecture• To describe
developments to web standards
• To briefly address implementation models
Aims of Talk• To give brief overview
of web architecture• To describe
developments to web standards
• To briefly address implementation models
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About UK Web Focus
UK Web Focus:
• JISC-funded post
• Advises UK HE community on web developments
• Represents JISC on World Wide Web Consortium (W3C)
• Organises events (e.g. national web managers workshop)
• Dissemination of information (e.g. see Web Focus column in Ariadne - http://www.ariadne.ac.uk/)
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Why Care About Standards?
This talk covers development of web standards, not web applications
An understanding of web standards is needed:• To appreciate when solutions are proprietary• To provide flexibility and interoperability• To avoid developing home-grown application solutions, when
protocol solutions are in the offing
The seminar is aimed at:• Web applications developers (e.g. CBL)• Developers of components of the Distributed National
Electronic Resource (DNER)• Web researchers• Other interested parties
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Standardisation
W3C• Produces W3C
Recommendations on Web protocols
• Managed approach to developments
• Protocols initially developed by W3C members
• Decisions made by W3C, influenced by member and public review
IETF• Produces Internet
Drafts on Internet protocols• Bottom-up approach to developments• Protocols developed by
interested individuals• "Rough consensus and working
code"
ISO• Produces ISO
Standards• Can be slow moving
and bureaucratic• Produce robust
standards
Proprietary• De facto standards• Often initially appealing
(cf PowerPoint, PDF)• May emerge as
standards
PNGHTMLZ39.50Java?
PNGHTMLZ39.50Java?
PNGHTMLHTTP
PNGHTMLHTTP
HTTPURNwhois++
HTTPURNwhois++
HTML extensionsPDF and Java?
HTML extensionsPDF and Java?
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The Web Vision
Tim Berners-Lee's vision for the Web:• Evolvability is critical • Automation of information management:
If a decision can be made by machine, it should• All structured data formats should be based on XML• Migrate HTML to XML• All logical assertions to map onto RDF model• All metadata to use RDF
See keynote talk at WWW 7 conference at <URL: http://www.w3.org/Talks/1998/0415-Evolvability/slide1-1.htm>
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HTML 4.0, CSS 2.0 and DOMHTML 4.0 used in conjunction with CSS 2.0 (Cascading Style Sheets) and the DOM provides an architecturally pure, yet functionally rich environment
HTML 4.0 - W3C-Rec• Improved forms• Hooks for stylesheets• Hooks for scripting
languages• Table enhancements• Better printing
CSS 2.0 - W3C-Rec• Support for all HTML
formatting • Positioning of HTML
elements• Multiple media support
Problems• Changes during CSS development• Netscape & IE incompatibilities • Continued use of browsers with
known bugs
Problems• Changes during CSS development• Netscape & IE incompatibilities • Continued use of browsers with
known bugs
DOM - W3C-Rec• Document Object Model• Hooks for scripting
languages• Permits changes to
HTML & CSS properties and content
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HTML Limitations
HTML 4.0 / CSS 2.0 have limitations:• Difficulties in introducing new elements
– Time-consuming standardisation process (<ABBREV>)
– Dictated by browser vendor (<BLINK>, <MARQUEE>)
• Area may be inappropriate for standarisation:– Covers specialist area (maths, music, ...)– Application-specific (<STUD-NUM>)
• HTML is a display (output) format• HTML's lack of arbitrary structure limits
functionality:– Find all memos copied to John Smith– How many unique tracks on Jackson Browne CDs
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XML
XML:• Extensible Markup Language• A lightweight SGML designed for network use• Addresses HTML's lack of evolvability• Arbitrary elements can be defined (<STUDENT-NUMBER>, <PART-NO>, etc)
• Agreement achieved quickly - XML 1.0 became W3C Recommendation in Feb 1998
• Support from industry (SGML vendors, Microsoft, etc.)
• Support in Netscape 5 and IE 5
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XML Deployment
Ariadne issue 15 has article on "What Is XML?"
Describes how XML support can be provided:
• Natively by new browsers
• Back end conversion of XML - HTML
• Client-side conversion of XML - HTML / CSS
• Java rendering of XML
Examples of intermediaries
See http://www.ariadne.ac.uk/issue15/what-is/See http://www.ariadne.ac.uk/issue15/what-is/
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XLink, XPointer and XSL
XLink will provide sophisticated hyperlinking missing in HTML:
• Links that lead user to multiple destinations• Bidirectional links• Links with special behaviours:
– Expand-in-place / Replace / Create new window– Link on load / Link on user action
• Link databases
XPointer will provide access to arbitrary portions of XML resource
XSL stylesheet language will provide extensibility and transformation facilities (e.g. create a table of contents)
EnglandFrance
<commentary xml:link="extended" inline="false"> <locator href="smith2.1" role="Essay"/> <locator href="jones1.4" role="Rebuttal"/> <locator href="robin3.2" role="Comparison"/> </commentary>
<commentary xml:link="extended" inline="false"> <locator href="smith2.1" role="Essay"/> <locator href="jones1.4" role="Rebuttal"/> <locator href="robin3.2" role="Comparison"/> </commentary>
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XML Update
Data / SchemasXML-Data: Submitted to W3C Jan 98 (Obsolete?)Document Content Description: Submitted Aug 98XSchema: Independent effort
Programming InterfaceDOM level 1: W3C Recommendation, May 98
Style & PresentationCSS level 2: W3C Recommendation, May 98Extensible Style Language: Working Draft, Aug 98
Relationship to Other ResourcesXLink , XPointer: Working Drafts, Mar 98XML Namespaces: Working Draft, Aug 98
Query LanguagesXML Query Language: Submitted to W3C Aug 98XQL: Independent effort
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Addressing
URLs (e.g. http://www.bristol-poly.ac.uk/depts/music/) have limitations:
• Lack of long-term persistency– Organisation changes name– Department shut down or merged– Directory structure reorganised
• Inability to support multiple versions of resources (mirroring)
URNs (Uniform Resource Names):• Proposed as solution• Difficult to implement (no W3C activity in this
area)
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Addressing - Solutions
DOIs (Document Object Identifiers):• Proposed by publishing industry as a solution• Aimed at supporting rights ownership• Business model needed
PURLs (Persistent URLs):• Provide single level of redirection
Pragmatic Solution:• URLs don't break - people break them• Design URLs to have long life-span
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TransportHTTP/0.9 and HTTP/1.0:
Design flaws and implementation problems
HTTP/1.1: Addresses some of these problems 60% server support Performance benefits! (60% packet traffic reduction) Is acting as fire-fighter Not sufficiently flexible or extensible
HTTP/NG: Radical redesign using object-oriented technologies Undergoing trials Gradual transition (using proxies) Integration of application (distributed searching?)
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MetadataMetadata - the missing architectural component from the initial implementation of the web
Metadata - RDF
PICS, TCN,
MCF, DSig,
DC,...
AddressingURL
Data formatHTML
TransportHTTP
Metadata Needs:• Resource discovery• Content filtering• Authentication• Improved navigation• Multiple format support• Rights management
Metadata Needs:• Resource discovery• Content filtering• Authentication• Improved navigation• Multiple format support• Rights management
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Metadata Examples
DSig (Digital Signatures initiative):• Key component for providing trust on the web• DSig 2.0 will be based on RDF and will support signed
assertion:– This page is from the University of Bath– This page is a legally-binding list of courses
provided by the University
P3P (Platform for Privacy Preferences):• Developing methods for exchanging Privacy Practices
of Web sites and user
Note that discussions about additional rights management metadata are currently taking place
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Sitemaps
Sitemaps provide navigational alternatives to browsing a site by following links.
Configurable site maps will enable end users to define hierarchies
http://www.elsop.com/linkscan/map.html
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RDF
RDF (Resource Description Framework):• Highlight of WWW 7 conference
• Provides a metadata framework ("machine understandable metadata for the web")
• Based on ideas from content rating (PICS), resource discovery (Dublin Core) and site mapping (MCF)
• Applications include:– cataloging resources – resource discovery– electronic commerce – intelligent agents– digital signatures – content rating– intellectual property rights – privacy
• See <URL: http://www.w3.org/Talks/1998/0417-WWW7-RDF>
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RDF ModelRDF:
• Based on a formal data model (direct label graphs)
• Syntax for interchange of data
• Schema model
Resource ValuePropertyType
Property
page.html £0.05Cost
11-May-98
ValidUntil
RDF Data Model
page.html £0.05
11-May-98
Property
Cost
InstanceOf
ValidUntil
ValuePropObj
Cost
PropName
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Browser Support for RDF
Mozilla (Netscape's source code release) provides support for RDF.
Mozilla supports site maps in RDF, as well as bookmarks and history lists
See Netscape's or HotWired home page for a link to the RDF file.
Trusted 3rd
Party Metadata
Embedded Metadata
e.g. sitemaps
Image from http://purl.oclc.org/net/eric/talks/www7/devday/Image from http://purl.oclc.org/net/eric/talks/www7/devday/
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RDF Conclusion
RDF is a general-purpose framework RDF provides structured, machine-
understandable metadata for the Web Metadata vocabularies can be developed
without central coordination RDF Schemas describe the meaning of
each property name Signed RDF is the basis for trust
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Distributed SearchingDistributed searching important for the DNER (Distributed National Electronic Resource)
ROADS prototype provides cross-searching using whois++
ROADS prototype provides cross-searching using whois++
AHDS prototype provides cross-searching using Z39.50
AHDS prototype provides cross-searching using Z39.50
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Distributed Searching Issues
Providing access to resources by software rather than by humans raises several issues:• Loss of service visibility / value-added web services• Possible performance problems• Information overload• Finding the service
Solutions:• Giving visibility and pointers in results sets• Service metadata:
–Service only available for cross-searching by non AC.UK users outside peak hours
• Need for agreed metadata standards (profiles, rights issues, …)
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Deployment Issues
How can new technologies be deployed?• Expect (hope) everyone will move to new
browsers• Use technologies in backwards-compatible
manner• Develop additional protocols e.g.
– Transparent Content Negotiation– CC/PP (see http://www.w3.org/TR/NOTE-CCPP)
• User-agent negotiation• Use of proxy intermediaries
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Intermediaries can provide functionality not available at client:
• DOI support• XML support / format conversion• Authentication
Intermediaries can provide functionality not available at client:
• DOI support• XML support / format conversion• Authentication
Deployment IssuesMore sophisticated deployment techniques can be adopted to overcome deficiencies in simple model
HTML resource
browserWeb server
Web server simply sends file to clientFile contains redundant information (for old browsers) plus client interrogation support
HTML / XML /
databaseresource browser
Server proxy
Client proxy
Original Model
Sophisticated Model
IntelligentWeb server
Example of an intermediary
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Conclusions
To conclude:• Standards are important, especially for national
initiatives and other large-scale services• Proprietary solutions are often tempting because:
– They are available– They are often well-marketed and well-supported– They may become standardised– Solutions based on standards may not be properly
supported by applications
• Metadata is big growth area• Intermediaries (brokers) likely to have a key role to
play in deploying standards-based solutions• Intelligent servers likely to be important
Recommended