Pragmatics of Declarative Ajax

XTech 2007, May 15-18, Paris 1

Pragmatics ofDeclarative Ajax

XTech 2007 May 15-18, ParisDave JohnsonCTO, [email protected]


Agenda

• Who Am I

• Rule of Least Power

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

• Summary


Who Is this Guy?

• Enterprise Ajax book (Addison Wesley)

• Nitobi Enterprise Ajax Podcast

• http://blogs.nitobi.com/dave


Anything Else?

• Nitobi CTO + Co-founder

• Located in Vancouver, Canada

• Declarative Ajax user-interface components for the enterprise


Nitobi Clients


Agenda

• Who Is this Guy?

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


The Rule of Least Power

• Tim Berners-Lee

• Noah Mendelsohn

• www.w3.org/2001/tag/doc/leastPower


Principle

“Powerful languages inhibit information reuse.”


Inhibiting Information Reuse

• Humans like complicated

• Pen and paper or memory stick?

• What does this have to do with the Web?


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/


WS-*???


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


110,000,000

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


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


Declarative Languages

• HTML

• XForms

• SVG

• MXML

• XAML

• JSON


Ham and Cheese

• “declarative” vs “imperative”

• “library” vs “roll your own”

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


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?


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!


Design VS Program

• Declarative “design” gets us 80%

• Programming gets the other 20%

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


Popular Tools

• HTML – how many HTML pages?

• JSON – relatively new compared to <XML>

• Microformats – hCard

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


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


Layering Languages

• Languages get more simple as we share more information

• Consider a factorial function in a few different languages?


Machine Code


Assembly

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


C++

int factorial(int n) {

if(n <= 1) return 1;

return n * factorial(n - 1);

}


Python

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


Still All Clearly Imperative

• Conditional statements

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


Agenda

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


Declarative User Interface

• Who cares about calculating factorials

• Power is in design


Declarative Maps?


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>


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>


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" />


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


The Bugaboo

• Imperative can be nearly as good as declaration

• “JavaScript objects need more than just setting properties”


var input = new Input();

input.hint = “Please enter a number”;

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

</input>


var input = new Input();

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

Input.prototype.setHint = function() {

// setup any event hooks etc…

}


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


Write Once, Deploy Anywhere

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


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


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>


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;}


Styling Namespaced Elements

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

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


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


Standards Approach

• Use HTML role attribute

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


W3C Accessibility

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

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


What are Others Doing?

• XML-Script

• Dojo Toolkit

• XForms


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>


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>


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>


Summary

• Declarative is “least power” approach

• Facilitates sharing of information

• User interface designability and skinnability are paramount


Q&A?

Dave Johnson

[email protected]

http://blogs.nitobi.com/dave

Pragmatics of Declarative Ajax

Business

Transcript of Pragmatics of Declarative Ajax