WWW/HTML BasicsCS 4173

What is the WWW?A distributed document delivery systemUses a client-server modelMain presentation language is HTML

Client-Server ModelTwo processes (possibly networked):The clientSends requests to the serverBlocks until reply is receivedThe serverProcesses requests from clientsNever blocksCan reply to several clients simultaneously

HTMLHypertext Markup LanguageIntended to be maximally portableLogical markupGraceful degradation of presentation

An ideal promoted by early WWWUsed to be more honoured in the breachIs it getting better now?

Markup LanguagesMarkup:Embedded codes in documentsCodes are called `tagsCodesDescribe the structure documentsInclude instructions for processingMarkup language:Computer language for describing syntax of tagsMay be used with other tools to specify rendering

Logical MarkupLogical markup:Describes parts of documentDoes not specify how to render

Example:This is very importantThis is very important

Logical Markup Presentation is clients `decisionWhen client cannot present then there is graceful degradation

Object example from Cougar

Some historyGopher & the Internet Superhighway

SGMLGML + Charles Goldfarb = SGMLeXtensible Markup Language

HTML

XML and XHTML

Why HTML became XHTMLHTML was originally a SGML applicationTags described the syntaxA DTD could check the syntaxInformal mapping from syntax to renderingMultiple incompatible versions aroseIETF moves at net speed not web $peedTag abuse was rampant in the netThey were a plague unto the users

Why HTML became XHTML (2)If you think IMG is bad

Big vendors (M$ and N$ mostly) agreedTo start overTo use eXtensible Markup LanguageA re-write of SGML emphasizing simplicityCarefully planned by CS savvy folksIncludes hooks for future development

XHTML BasicsVery few real changes from HTMLBut more strict

All tags are in lowercaseAll tags must be closed Empty tagsPaired tags

XHTML Basics3 Parts to an XHTML or HTML documentDOCTYPEWhat DTD are you usingHeadMeta informationOnly is requiredBodyText to render

XHTML Document Structure

XHTML BasicsTagsElementsAttributesEntities,&, ,,,, etc.See example at CS4173 websiteComments

s is (the non-breaking space)

XHTML Tags vs. ElementsTag is markup to represent an element

Logical vs. Presentation ElementsTT CODE, KBD, PRE?B/IT/U EM/STRONGListsUL/OLDL

XHTML Tags vs. ElementsBlock-level and in-line elementsTABLE, P, BLOCKQUOTE, DIV, etc.CODE, Q, H1, SPAN, etc.Grouping ElementsDIVSPANOne-part elementsBR, etc.

XHTML Tags vs. ElementsBrowser-specific tags

MARQUEE, BLINK, etc.

What happens when a browser doesn't recognize a tag?

XHTML BasicsTags may be nested but Tags may not overlap

Overlap versus Nesting

Links Why The WWW Is HTA elementHREFNAMECLASSRELTYPEURIs and URLsRFCs

TITLEIDSTYLEAnchor TextTABINDEX

Where are the tools?HTML Tidy/opt/bin/tidy on borg

The validatorhttp://validator.w3.org/http://www.cs.dal.ca/validator?http://www.cs.dal.ca/validate?http://www.cs.dal.ca:81?

XHTML/HTML ExamplesXHTML element sampler XHTML sample template

Both in the examples section of the website

For More About HTMLRFC 1866 (HTML 2.0) (at faqs.org)

Explains some of the philosophy behind HTML

HTML 4.01 (at W3C)

Last version of HTML

XHTML 1.1 (at W3C)

Modularized XHTML

So many choices!

Which Standard to Follow?Minimal standard for this course is HTML 4.01 TransitionalPreferred standard is XHTML 1.0 or 1.1

See Picking a Rendering ModeBy Eric MeyerIn the Readings part of the Resources

Here endeth the lesson

s is (the non-breaking space)