pragmatics of declarative ajax

XTech 2007, May 15-18, Paris 1

Pragmatics ofDeclarative Ajax

XTech 2007 May 15-18, ParisDave JohnsonCTO, Nitobidave@nitobi.com

XTech 2007, May 15-18, Paris 2

Agenda

• Who Am I

• Rule of Least Power

• Declarative Languages– Programming Basics– Web User Interfaces– Common Problems

• Summary

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Who Is this Guy?

• Enterprise Ajax book (Addison Wesley)

• Nitobi Enterprise Ajax Podcast

• http://blogs.nitobi.com/dave

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Anything Else?

• Nitobi CTO + Co-founder

• Located in Vancouver, Canada

• Declarative Ajax user-interface components for the enterprise

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Nitobi Clients

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Agenda

• Who Is this Guy?

http://flickr.com/photos/jjd/24164311/

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The Rule of Least Power

• Tim Berners-Lee

• Noah Mendelsohn

• www.w3.org/2001/tag/doc/leastPower

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Principle

“Powerful languages inhibit information reuse.”

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Inhibiting Information Reuse

• Humans like complicated

• Pen and paper or memory stick?

• What does this have to do with the Web?

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Good Practice

“Use the least powerful language suitable for expressing information, constraints or

programs on the World Wide Web.”

XTech 2007, May 15-18, Paris 12http://www.flickr.com/photos/doglotion/154496890/

XTech 2007, May 15-18, Paris 13http://www.flickr.com/photos/dpade1337/429996161/

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WS-*???

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Benefits of Less Power?

• More robust and secure

• Easier for people to use

• Therefore, more people use them

• Be mindful of the success of HTML

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110,000,000

XTech 2007, May 15-18, Paris 17http://flickr.com/photos/oceanyamaha/186146223/

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Declarative What?

• It is about what not how

• There is no sign of an algorithm

• We are not talking functional languages

• HTML – canonical declarative language

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Declarative Languages

• HTML

• XForms

• SVG

• MXML

• XAML

• JSON

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Ham and Cheese

• “declarative” vs “imperative”

• “library” vs “roll your own”

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XTech 2007, May 15-18, Paris 22http://www.flickr.com/photos/refractedmoments/399890975/

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Computability

• But is the Jambon et Fromage Touring complete?

• You can’t change the recipe

• If there is no way to specify what you want to do then how can you do it?– Make the sandwich yourself– Bring your own mustard

• Why bother?

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Pareto’s Principle

• Call it what you will– 80-20 rule– Law of the vital few– Principle of factor sparsity– 90-10 rule in software engineering

• Declarative gets you most of the way!

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Design VS Program

• Declarative “design” gets us 80%

• Programming gets the other 20%

• One of two evils– Easy to design– Easy to program

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Popular Tools

• HTML – how many HTML pages?

• JSON – relatively new compared to <XML>

• Microformats – hCard

• Twitter – how many messages?– Twitter vision L:Paris

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Not Just About XML

• Declarative does not have to be XML

• Imperative languages can look declarative– Using imperative language to encapsulate

non-declarative ideas

• You don’t have to bake the bread for your sandwich … nor mill the grain

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Layering Languages

• Languages get more simple as we share more information

• Consider a factorial function in a few different languages?

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Machine Code

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Assembly

main:movl $5, %eaxmovl $1, %ebxL1: cmpl $0, %eaxje L2imull %eax, %ebxdecl %eaxjmp L1L2: ret

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C++

int factorial(int n) {

if(n <= 1) return 1;

return n * factorial(n - 1);

}

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Python

fac = lambda n:[1,0][n>0] or fac(n-1)*n

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Still All Clearly Imperative

• Conditional statements

• However, once you start using the factorial function it appears declarative

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Agenda

http://flickr.com/photos/stevecaddy/474542238/

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Declarative User Interface

• Who cares about calculating factorials

• Power is in design

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Declarative Maps?

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In JavaScript<script type=“text/javascript”>gmap.init = function() { var map = new GMap2(document.getElementById("map")); map.setCenter(new GLatLng(49.290327, -123.11348), 12); var polyline = new GPolyline([ new GLatLng(49.265788, -123.069877), new GLatLng(49.276988, -123.069534), new GLatLng(49.276988, -123.099746), new GLatLng(49.278108, -123.112106), new GLatLng(49.2949043, -123.136825)], "#ff0000", 10); map.addOverlay(polyline); }window.onload = gmap.init;</script>

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In (X)HTML

<g:map id="map" width="370px" height="380px" smallmapcontrol="true" maptypecontrol="true">

<g:center zoom="14"> <g:point lat="49.2853" lng="-123.11348"></g:point> </g:center> <g:polyline color="#FF0000" size="10"> <g:point lat="49.265788" lng="-123.069877"></g:point> <g:point lat="49.276988" lng="-123.069534"></g:point> <g:point lat="49.276988" lng="-123.099746"></g:point> <g:point lat="49.278108" lng="-123.112106"></g:point> <g:point lat="49.294904" lng="-123.136825"></g:point> </g:polyline></g:map>

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Same but Different

new GLatLng(49.265788, -123.069877)

<g:point lat="49.265788" lng="-123.069877" />

new GLatLng(-123.069877, 49.265788)

<g:point lng="-123.069877" lat="49.265788" />

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Practical Differences

• Both could have auto-complete support• Designability and IDE support• HTML writer support on servers• Order matters … to a less degree in XML• Declarative can be less code• People don’t like JavaScript• Remember, HTML is a success for a

reason

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The Bugaboo

• Imperative can be nearly as good as declaration

• “JavaScript objects need more than just setting properties”

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var input = new Input();

input.hint = “Please enter a number”;

<input><hint>Please enter a number</hint>

</input>

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var input = new Input();

input.setHint(“Please enter a number”);

Input.prototype.setHint = function() {

// setup any event hooks etc…

}

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Benefits?

1. Designable• easy IDE tooling

2. Declarative patterns• succinct, reproducible solutions

3. Rich semantics• frameworks can easily read and interpret• server or client side interpretation

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Write Once, Deploy Anywhere

XTech 2007, May 15-18, Paris 46http://flickr.com/photos/elmyra/9335163/

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Problems

• Firefox – served as HTML– DOM traversal– Self closing tags

• Internet Explorer – can’t be served as XHTML– DOM methods– Namespace

• Namespaces– XHTML– CSS

• Validation

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Firefox HTML DOM Traversal<div id="div1"> <ntb:button id="button1">button</ntb:button> <ntb:button id="button2">button 2</ntb:button> <ntb:panel id="panel1"> <ntb:title id="title1"> <div id="div2">panel title 1</div> </ntb:title> <ntb:contents id="contents1"> <div id="div3">Contents div3</div> <div id="div4">Contents div4</div> </ntb:contents> </ntb:panel></div>

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getElementsByTagNameNSns.getElementsByTagNameNS = function(tag, np, context) { context = context || document; var qname = np + ":" + tag; if (ns.IE) qname = tag; var elems = context.getElementsByTagName(qname); if (ns.IE) { realElems = []; for (var i=0; i<elems.length; i++) { if (elems[i].scopeName == ns) realElems.push(elems[i]); } elems = realElems; } return elems;}

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Styling Namespaced Elements

• Internet Explorerntb\:* { display:none;}

• W3C@namespace ntb "http://www.nitobi.com";ntb|* { display:none;}

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Other Approaches

• Custom attribute– <div oatype="ntb:grid" ... />

• Microformats– <div class=“ntb_grid” … />

• XBL / HTC• JSON

– <div oatype=“{widget:’grid’,colums:[‘Col1’,Col2’]}” />

• Many, many more

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Standards Approach

• Use HTML role attribute

• Accessibility of Rich Internet Applications (ARIA) as part of Web Accessibility Initiative

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W3C Accessibility

• tabindex="-1"• role="wairole:checkbox"• property:checked="true“

<div tabindex=“-1” role=“wairole:checkbox” property:checked=“true”></div>

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What are Others Doing?

• XML-Script

• Dojo Toolkit

• XForms

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XML-Script<script type="text/xml-script"> <page xmlns="http://schemas.microsoft.com/xml-script/2005"> <components> <textbox id="searchText" /> <button id="searchButton"> <bindings> <binding property="enabled" dataContext="searchText"

dataPath="text.length" transform="NumberToBoolean" /> </bindings> <click> <invokeMethod target="searchMethod" method="invoke" /> </click> </button> <serviceMethod id="searchMethod"> <bindings> <binding property="parameters" propertyKey="query"

dataContext="searchText" dataPath="text" /> </bindings> </serviceMethod> </components> </page></script>

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Dojo Toolkit

<BUTTON widgetId="helloButton" dojoType="Button">Hello World!</BUTTON>

<?xml:namespace prefix=dojo/>

<dojo:widget></dojo:widget>

<DIV dojoType="widget">

<DIV class=dojo-widget></DIV>

</DIV>

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XForms<html xmlns="http://www.w3.org/1999/xhtml" xmlns:f="http://www.w3.org/2002/xforms"> <head> <title>Search</title> <f:model> <f:submission action="http://example.com/search“

method="get" id="s"/> </f:model> </head> <body> <p> <f:input ref="q"><f:label>Find</f:label></f:input> <f:submit submission="s"><f:label>Go</f:label></f:submit> </p> </body></html>

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Summary

• Declarative is “least power” approach

• Facilitates sharing of information

• User interface designability and skinnability are paramount

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Q&A?

Dave Johnson

dave@nitobi.com

http://blogs.nitobi.com/dave