Transcript Powerpoint 97 format

Web Standards
Brian Kelly
UK Web Focus
UKOLN
University of Bath
1
Email Address
[email protected]
URL
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.
Contents
• Introduction
• Web Standards Overview
• Web Standards:
• Data Formats
• Transport
• Addressing
• Metadata
• Distributed Searching
• Deployment Issues
2
Aims of Talk
• To give brief overview
of web architecture
• To describe
developments to web
standards
• To briefly address
implementation models
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/)
3
Why Care About Standards?
4
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
Standardisation
HTML
Proprietary
extensions
• De facto standards
PDF and Java? • Often initially appealing
(cf PowerPoint, PDF)
W3C
PNG
•
May
emerge
as
• Produces W3C
HTML
ISO
standards
Recommendations
• Produces ISO Z39.50
on Web protocols
Java?
Standards
• Managed approach to
• Can be slow moving
developments
and bureaucratic
• Protocols initially
• Produce robust
IETF
developed by
standards
W3C members
• Produces Internet
• Decisions made by
Drafts on Internet protocols
W3C, influenced by
• Bottom-up approach to developments
member and public
• Protocols developed by
HTTP
review
interested
individuals
PNG
URN
•
"Rough
consensus
and
working
HTML
whois++
code"
HTTP
5
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 DOM
HTML 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
Problems
• Changes during CSS development
• Netscape & IE incompatibilities
• Continued use of browsers with
known bugs
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CSS 2.0 - W3C-Rec
• Support for all HTML
formatting
• Positioning of HTML
elements
• Multiple media support
DOM - W3C-Rec
• Document Object Model
• Hooks for scripting
languages
• Permits changes to
HTML & CSS properties
and content
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:
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– Find all memos copied to John Smith
– How many unique tracks on Jackson Browne CDs
XML
XML:
•
•
•
•
Extensible Markup Language
A lightweight SGML designed for network use
Addresses HTML's lack of evolvability
Arbitrary elements can be defined (<STUDENTNUMBER>, <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/
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XLink, XPointer and XSL
XLink will provide sophisticated
England
hyperlinking missing in HTML:
France
• 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
<commentary xml:link="extended" inline="false">
• Link databases
<locator href="smith2.1" role="Essay"/>
<locator href="jones1.4" role="Rebuttal"/>
XPointer will provide
<locator href="robin3.2" role="Comparison"/>
access to arbitrary
</commentary>
portions of XML resource
XSL stylesheet language will provide extensibility and
transformation facilities (e.g. create a table of contents)
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XML Update
Data / Schemas
XML-Data: Submitted to W3C Jan 98 (Obsolete?)
Document Content Description: Submitted Aug 98
XSchema: Independent effort
Programming Interface
DOM level 1: W3C Recommendation, May 98
Style & Presentation
CSS level 2: W3C Recommendation, May 98
Extensible Style Language: Working Draft, Aug 98
Relationship to Other Resources
XLink , XPointer: Working Drafts, Mar 98
XML Namespaces: Working Draft, Aug 98
Query Languages
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XML Query Language: Submitted to W3C Aug 98
XQL: Independent effort
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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Transport
HTTP/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:




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Radical redesign using object-oriented technologies
Undergoing trials
Gradual transition (using proxies)
Integration of application (distributed searching?)
Metadata
Metadata - the missing architectural component
from the initial implementation
of the web
Addressing
URL
Metadata Needs:
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•
•
•
•
•
•
Resource discovery
Content filtering
Authentication
Improved navigation
Multiple format support
Rights management
Transport Data format
HTTP
HTML
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
17
Sitemaps
Sitemaps provide
navigational alternatives to
browsing a site by following
links.
Configurable site
maps will enable
end users to define
hierarchies
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http://www.elsop.com/
linkscan/map.html
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:
–
–
–
–
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cataloging resources
electronic commerce
digital signatures
intellectual property rights
– resource discovery
– intelligent agents
– content rating
– privacy
• See <URL: http://www.w3.org/
Talks/1998/0417-WWW7-RDF>
RDF Model
RDF Data Model
RDF:
• Based on a formal
data model (direct
label graphs)
• Syntax for
interchange of data
• Schema model
page.html
Cost
Resource
Property
PropName
Cost
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Value
Property
page.html
£0.05
PropObj
InstanceOf
PropertyType
Value
ValidUntil
11-May-98
Cost
£0.05
ValidUntil
11-May-98
Browser Support for RDF
Trusted
Mozilla (Netscape's
3rd
source code release) Party
provides support for Metadata
RDF.
Mozilla supports site
maps in RDF, as well
as bookmarks and
history lists
Embedded
See Netscape's or
Metadata
HotWired home page e.g.
sitemaps
for a link to the RDF
file.
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, machineunderstandable 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
22
Distributed Searching
Distributed searching important for the DNER
(Distributed National Electronic Resource)
ROADS prototype provides
cross-searching using whois++
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AHDS prototype provides
cross-searching using Z39.50
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
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• Need for agreed metadata standards (profiles, rights
issues, …)
Deployment Issues
How can new technologies be deployed?
• Expect (hope) everyone will move to new
browsers
• Use technologies in backwardscompatible 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
25
Deployment Issues
More sophisticated deployment techniques can be
adopted to overcome deficiencies in simple model
Original Model
HTML
resource
Web
server
browser
Sophisticated Model
HTML /
XML /
database
resource
Intelligent
Web
server
Intermediaries can provide
functionality not available at client:
• DOI support
• XML support / format conversion
26 • Authentication
Web server simply sends
file to client
File contains redundant
information (for old
browsers) plus client
interrogation support
Client
proxy
browser
Server
proxy
Example of an intermediary
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
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