1 The Latest Web Developments: How Do I Deploy Them? Brian Kelly Email Address UK Web Focus [email protected]UKOLN 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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1 The Latest Web Developments: How Do I Deploy Them? Brian KellyEmail Address UK Web Focus [email protected] UKOLN University of Bath
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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
• Background
• Web Developments:• Data Formats• Transport• Addressing• Metadata
• Deployment Issues
• Questions
Aims of Talk• To give an overview of
the Web architecture• To review new web
developments• To address
implementation models
Aims of Talk• To give an overview of
the Web architecture• To review new web
developments• To address
implementation models
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Background
UK Web Focus:• National web coordination post based at UKOLN,
University of Bath• Responsible for tracking web developments and
informing and advising UK HE community• Represents JISC on W3C
W3C (World Wide Web Consortium):• International organisation responsible for
coordinating web standards• See <URL: http://www.w3.org/>• See list of recommendations, working drafts and
notes at <URL: http://www.w3.org/TR/>
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Web and 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
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)• May emerge as
standards
PNGHTMLZ39.50Java?
PNGHTMLZ39.50Java?
PNGHTMLHTTP
PNGHTMLHTTP
HTTPURN
HTTPURN
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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Web Protocols
Web initially based on three simple protocols:
• Data FormatsHTML (HyperText Markup Language) provides the data format for native documents
• AddressingURLs (Uniform Resource Locator) provides an addressing mechanism for web resources
• TransportHTTP (HyperText Transfer Protocol) defines transfer of resources between client and server
Data FormatHTML
AddressingURL
TransportHTTP
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HTML History
HTML 1.0 Unpublished specification.
HTML 2.0 Spec. based on innovations from NCSA (forms and inline images!)
HTML 3.0 Proposed spec. (renamed from HTML+).Very comprehensive Failed to complete IETF standardisation Little implementation experience
Proprietary Introduction of proprietary HTML elements by Netscape and Microsoft
HTML 3.2 Spec. based on description of mainstream innovations in marketplace
HTML 4.0 Current recommendation1998
1994
1997
1994-5
1995
1992
DilemnaProprietary extensions
cause problems.But experiments
are needed
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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
CSS Problems• Changes during CSS development• Netscape & IE incompatibilities • Continued use of browsers with
known bugs
CSS Problems• Changes during CSS development• Netscape & IE incompatibilities • Continued use of browsers with
known bugs
DOM : W3C-WD• Document Object Model• Hooks for scripting
languages• Permits changes to
HTML & CSS properties and content (DHTML)
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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.)• Various XML DTDs already agreed (MathML, CML)• Support in Netscape 5 and IE 5
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XML Concepts
Well-formed XML resources:Make end-tags explicit: <LI>...</LI>
Make empty elements explicit: <IMG .../>
Quote attributes <IMG SRC="logo" HEIGHT="20"
Use consistent upper/lower case
Valid XML resources:
Need DTD
XML Namespaces:Mechanism for ensuring unique XML elements:<?xml:namespace ns="http://foo.org/1998-001" prefix="i">
<P>Insert <i:PART>M-471</i:PART></P>
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XML Deployment
Ariadne issue 14 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 behaviors:
– 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.Interesting IPR issues!
XSL stylesheet language will provide extensibility and transformation facilities (e.g. create a table of contents)
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
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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Deployment Issues
Various interesting new technologies have been outlined
How can they be deployed in our environment?
Should we:• Ignore them?• Accept them fully?• Accept them partly?
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Ignore New Developments
We can chose to ignore new developments, and continue to use HTML 3.2:
Safe option, with no new training, support or software costs
Experience in effectiveness, limitations, etc. Fails to address current performance problems Fails to address accessibility problems Fails to provide new functionality Service likely to look "old-fashioned" compared
with competition
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Fully Accept New Developments
We can chose to more wholesale to, say, HTML 4.0 and CSS 2.0:
Can be exciting to be at leading edge Performance benefits Accessibility benefits Based on open-standards Provides motivation for users to upgrade browsers Likely to be solution at some point (cf. Gopher) Backwards compatibility problems with old browsers Costly to deploy new authoring news, training, .. Likely to be bugs and incompatibilities with new
tools and browsers
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Implement "Safe" Solutions
An alternative is to use "safe" parts of technologies which are backwards compatible and avoid major browser bugs
Attractive sounding compromise position Lose some functionality, but not all Can be difficult or expensive to find "safe" options
(does .margin-left work on IE on SGI?) Tools may not allow safe options to be chosen Lack of validation tools for checking conformance
with restricted set of specification
Note
See <URL: www.webreview.com/guides/style/insafegrid.htm> for unsafe CSS 2.0 properties
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Decision Time
What would you opt for?
Stick with current technologiesCheap, default option. Continuation of performance and accessibility problems. Unlikely to be long term solution.
Deploy new technologiesMore expensive option. Functionality, performance and accessibility benefits. Access problems for old browsers.
Use "safe" new technologiesMay require home-grown tools and support. Avoids some of the problems of other solutions
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An Alternative
An alternative approach to deploying new technologies is available:
• Use more intelligent server-side software• Use "proxies" to address limitations of
browser technologies. The term intermediary was used in a paper [1] at the WWW 7 conference to describe this approach
• Protocol solutions, such as Transparent Content Negotiation (TCN)
[1] "Intermediaries: New Places For Producing and Manipulating Web Content"
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Intelligent Server Software
Simple model:• Server receives request for resource• Server delivers resource to client
More sophisticated model:• Server receives request for resource • Server processes header information from client• Server delivers resource to client based on client
information
This is referred to as browser-sniffing or user-agent negotiation
Note that server support is now available in Apache and in server add-ons such as PHP/FI and MS Active Server Pages
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Portion of CSS file for IETotal 797 lines
W3C CSS Gallery
W3C have a link to a core style sampler service.
The service provides 8 core style sheets which can be freely linked to.
The style sheets use "browser sniffing". Different style sheets are delivered to different browsers.