developing web applications with xhtml: problems and benefits ian graham senior manager, esolutions...

Developing Web Applications With XHTML:

Problems and Benefits

Ian GRAHAMSenior Manager, eSolutions Group Emfisys, Bank of MontrealE: [email protected] or utoronto.ca}W: http://www.utoronto.ca/ian/talks/T: 416.513.5656 / F: 416.513.5590

Talk Outline

Introduction Technical and process issues

Browsers and XHTMLServer-side data managementDynamic content generationConclusions

Browsers and XHTML

Data delivered to browsers as one of two MIME types text/html (HTML data) text/xml (XML data)

Two types handled in very different ways

Browsers and XHTML

HTML Channel Support

Navigator 1--6 Opera 3--6 Lynx IE 3--5.5 ... Basically every

browser

XML Channel Support

Navigator 6 IE 5/5.5 Opera 4

Fewer browsers, with caveats (rendering / processing problems)

HTML vs. XML Channels

HTML channel XML channelLarge set of defined internal general entities forcommon non-ASCII characters and symbols

Only 5 XML-standard predefined generalentities (lt, gt, amp, apos, and quot)

Default formatting properties for all standardHTML elements

No default XHTML formatting properties(exception: Mozilla/Navigator 6)

CSS support for id- and class-based CSSselectors (e.g., div.special, pre#note)

No support

Hard-wired support for functional elements(links, replaced elements [img, object/applet],map etc.)

No support (some support in Mozilla)

No internal DTD subsets: some browserssupports DOCTYPE declarations with nointernal subset (for rendering mode switching)

Supports internal DTD subsets andarbitrary entity declarations, both internaland (sometimes) external

No validation Supports DTD-based (and sometimesschema-based) validation

must omit CDATA sections Supports CDATA sectionsN/A Supports an XML declarationNo namespace support Supports namespaces

XHTML via XML Channel

Mozilla/NN6 “namespace” support

for XHTML namespace

– default formatting properties

Restricted CSS support

No support (yet) for style, link elements

– <?xml-stylesheet .... ?>

IE 5/5.5 No special support for

XHTML (use CSS+XML)

No standardized support for functional markup

Transform XML into HTML:XML+XSLT HTML

Browser Conclusions:

Deliver data as text/htmlMust avoid many XML features

CDATA sections DTD internal subsets (and DTD functionality)

Not supported by HTML processors

XHTML as text/html

Be aware of some XHTML features xml:lang vs. lang attributes (use both) XML declarations (avoid them) empty element tag notation (add space

before trailing “/” character) non-minimized attribute assignments (some

bugs with Opera 3.6) DTD declaration (rendering concerns)

“Safe” XHTML example

<?xml version= "1.0" encoding= "utf-8" ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd" ><html xmlns= "http://www.w3.org/1999/xhtml1" xml:lang= "en-ca" lang= "en-ca" ><head><title> ... </title><meta http-equiv= "content-type" content= "text/html;charset=utf-8" /></head><body>.....</body></html>

whitespacebefore slash

DOCTYPE Switching

New HTML processors render differently depending on DOCTYPE value:

“quirks” mode -- (reproduces various CSS and other layout “errors” of older browsers)

“standards” mode -- (correct behavior, no quirks [supposedly!] )

DOCTYPE Switching

All XHTML DTDs get “standard” mode. Thus the following rule:

quirks mode: omit DOCTYPE strict mode: include an XHTML

DOCTYPE declaration

Summary

Seems like a lot of problems....Not so bad ...

Have to deal with most anyway (e.g., quirky vs. strict)

“patching” often easy to automateBenefits

Reduced markup errors (well-formedness) Migration path to future delivery channels

Markup Guidelines

Use external scripts and CSS style sheetsAvoid CDATA sectionsExternal script, style sheet filesOn output, auto-adjust syntax:

insert space at end of empty-element tags duplicate lang-related attributes strip/insert appropriate DOCTYPE declaration strip XML declaration

Talk Outline

IntroductionBrowsers and XHTMLServer-side data managementDynamic content generationConclusions

Server-Side Management

XHTML reduces errors in composition and rendering phases Well-formedness ensures unambiguous

processing by an HTML or XML processor Barring CSS errors, this means fewer

browser formatting problems

Problems support by content generation tools

Issues:

Limited pool of XHTML authoring tools Most popular page authoring tools designed

for HTML (DreamWeaver, FrontPage etc.) XHTML conversion adds process steps to

authoring– Too complex for most Web authors/designers

Not an issue for organizations with existing XML/SGML processes

Processing Content

Author /edit

View &verify

Publishcontent

Problem detected

A)

Problem detected

Author /edit

View &verify

Publishcontent

Convertto

XHTMLB)

Alternatives

Use XML-aware authoring tools Issues: Cost, non-WYSIWYG nature

Create tightly controlled page “templates” and limit authoring responsibilities Reduces likelihood of markup error

Dynamic content generation Fragment authoring only -- with validation

Talk Outline


Dynamic Content

Content from databases SQL, XML, files (plain text or XML fragments)

Can enforce well-formedness in software Either via structured markup generating

functions or true XML-based tools

Reduced numberof markup/formattingerrors


XHTMLFragment

XHTMLFragment

XHTMLFragment

HTML / XHTML

pagetemplate

Page generationengine

HTML / XHTML

tobrowser

text strings

XHTML Fragments

XHTML helps reduce errors in composition of pages from fragments: Checking fragment well-formedness ensures

well-formedness of composed content

Even if template is not well-formed, well-formedness of fragments increases rendering reliability of composed product

Easier to control fragment authoring

Roles & Responsibilities

Fragment creation Many individual writers; requires little markup

knowledge; WYSIWYG often not as importantTemplate creation / Management

Fewer, more technically skilled people; can enforce well-formedness

Fragment Creation

Common use case in content creatione.g., Newspaper articles, weblogs

Subset of XHTML (e.g., p, a, br, h3, b, i, img, em)

few attributes Easy to write Easy to dynamically “correct” markup

Example Web Interface

Advantages

• Centralized code • Single interface

Disadvantages

• Crappy editor• Need to know markup to write content

Future Alternatives

Editable Web content (IE 5.5, Mozilla) http://standardbrains.editthispage.com/

Accessing DOM tree to build an editor DOM ensures validity / well-formedness of

markup

With Mozilla, will work with XML

Content Assembly

Many tools (JSP, php, ASP, zope ...) Not many that guarantee well-formed XML

output Obvious choice: XSLT

Guarantees well-formedness of output HTML output mode allows for most issues

described earlier


XHTMLFragment

XHTMLFragment

XHTMLFragment

XSLTpage

template

XSLT processor

XHTMLto

browser

Zero markup / formatting errors

text strings

XSLTfragmenttemplate

XSLT

(2)

Output(2)

XSLT Advantages

Always well-formed! Abstraction layer

between content and output Easier adjustment for

future delivery channels

XSLT

(1)

XSLT

Output(1)

XSLT Caveats

Non-trivial language (well, at least to page developers/designers)

Unclean separation between designer and programmer

Lack of easy integration to common editing tools

Alternative Approach

“Procedural” page template designs XHTML-compliant design tools

Escape to XSLT for content “components” “Prototype-based” transformations

Markup Model

...regular markup ....<xsl:prototype> <table> ... Example table content goes here ... </table></xsl:prototype>... More XHTML markup ....

Talk Outline


Conclusions

XHTML provides pragmatic advantages Improved content reliability, at several layers;

migration path to XML-centric world

Several disadvantages in near-term Poor integration with authoring tools; no easy

XSLT-design separation

Developing Web Applications With XHTML:Problems and Benefits

Ian GRAHAMSenior Manager, eSolutions Group Emfisys, Bank of MontrealE: ian.graham@{bmo.com or utoronto.ca}W: http://www.utoronto.ca/ian/talks/T: 416.513.5656 / F: 416.513.5590

developing web applications with xhtml: problems and benefits ian graham senior manager, esolutions...

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