XForms and the Semantic Web
Steven Pemberton
CWI and W3C
Kruislaan 413
1098 SJ Amsterdam
The Netherlands
Steven.Pemberton@cwi.nl
www.cwi.nl/~steven
About the Instructor
Steven Pemberton is a researcher at the CWI, The Centre for Mathematics
and Computer Science, a nationally-funded research centre in Amsterdam, The
Netherlands, the first non-military Internet site in Europe.
Steven's research is in interaction, and how the underlying software
architecture can support the user. At the end of the 80's he built a
style-sheet based hypertext system called Views.
Steven has been involved with the World Wide Web since the beginning. He
organised two workshops at the first World Wide Web Conference in 1994,
chaired the first W3C Style Sheets workshop, and the first W3C
Internationalisation workshop. He was a member of the CSS Working Group from
its start, and is a long-time member (now chair) of the HTML Working Group,
and co-chair of the XForms Working Group. He is co-author of (amongst other
things) HTML 4, CSS, XHTML and XForms.
Steven is also Editor-in-Chief of ACM/interactions.
Objectives
HTML Forms, introduced in 1993, were the basis of the e-commerce
revolution. After 10 years experience, it has become clear how to improve on
them, for the end user, the author, and the owners of the services that the
forms are addressing. XForms is a new technology, announced in October 2003,
intended to replace HTML Forms.
The advantages of XForms include:
- It improves the user experience: XForms has been designed to allow much
to be checked by the browser, such as types of fields being filled in, or
that one date is later than another. This reduces the need for round
trips to the server or for extensive script-based solutions, and improves
the user experience by giving immediate feedback to what is being filled
in.
- It is XML, and it can submit XML.
- It combines existing XML technologies: Rather than reinventing the
wheel, XForms uses a number of existing XML technologies, such as XPath
for addressing and calculating values, and XML Schemas for defining data
types. This has a dual benefit: ease of learning for people who already
know these technologies, and implementors can use off-the-shelf
components to build their systems.
- It is internationalized.
- It is accessible: XForms has been designed so that it will work equally
well with accessible technologies (for instance for blind users) and with
traditional visual browsers.
- It is device independent: The same form can be delivered without change
to a traditional browser, a PDA, a mobile phone, a voice browser, and
even some more exotic emerging clients such as an Instant Messenger. This
greatly eases providing forms to a wide audience, since forms only need
to be authored once.
- It is easier to author complicated forms.
The presenter is one of the authors of the XForms specifications, and is
chair of the Forms Working Group that produced the technology.
This tutorial works from a basis of HTML Forms, and introduces XForms
step-by-step. It covers essentially all of XForms except some technical
details about events, and no more than a passing reference to the use of
Schemas.
Emphasis is on how to improve the user experience, and how XForms improves
accessibility and device independence, and makes the author’s life easy in
producing a better experience.
HTML Forms
- Presentation oriented, mixing data and presentation
- No types, Ping-ponging to the server
- Reliance on scripting
- Problems with non-Western characters
- Accessibility problems
- Hard to make cross-device for single authoring
- Impoverished data-model, no integration with existing streams
- Hard to manage, hard to see what is returned
- No support for wizards and shopping carts etc.
Soundbite: "Javascript accounts for 90% of our headaches in complex
forms, and is extremely brittle and unmaintainable."
The Approach
The essence is to separate what is being returned from how the values are
filled in.
The model specifies the values
being collected (the instance), and their related logic:
- Types, restrictions
- Initial values, Relations between values
- The body of the document then binds forms controls to
values in the instance
- The controls only reflect their intent
Basic structure of XForms
Take this simple HTML form:
<html>
<head><title>Search</title></head>
<body>
<form action="http://example.com/search"
method="get">
Find <input type="text" name="q">
<input type="submit" value="Go">
</form>
</body>
</html>
The main difference in XForms is that details of the values collected and
how to submit them are gathered in the head, in an element called
model
; only the form controls are put in the body.
... basic structure
So the equivalent XForm is:
<model>
<instance><data xmlns=""><q/></data></instance
<submission
action="http://example.com/search"
method="get"
id="s"/>
</model>
The <form>
element is now no longer needed; the
controls in the body look like this:
<input ref="q"><label>Find</label></input>
<submit submission="s">
<label>Go</label>
</submit>
Complete XForms search example
<h:html xmlns:h="http://www.w3.org/1999/xhtml"
xmlns="http://www.w3.org/2002/xforms">
<h:head>
<h:title>Search</h:title>
<model>
<instance><data xmlns=""><q/></data></instance>
<submission
action="http://example.com/search"
method="get" id="s"/>
</model>
</h:head>
<h:body>
<h:p>
<input ref="q"><label>Find</label></input> <submit submission="s"><label>Go</label>
</submit>
</h:p>
</h:body></h:html>
'Editing' any XML document
- External instances give you immense power
- The
ref
attribute can be any XPath expression
- XPath lets you select any element or attribute in an XML document
- You can bring in any XML document as instance, even an XHTML
document
Editing example
Suppose a shop has very unpredictable opening hours (perhaps it depends on
the weather), and they want to have a Web page that people can go to to see
if it is open. Suppose the page in question has a
single paragraph in the body:
<p>The shop is <strong>closed</strong> today.</p>
Well, rather than teaching the shop staff how to write HTML to update
this, we can make a simple form to edit the page
instead:
Editing XHTML page
<model>
<instance
src="http://www.example.com/shop.xhtml"/>
<submission
action="http://www.example.com/shop.xhtml"
method="put" id="change"/>
</model
...
<select1 ref="/h:html/h:body/h:p/h:strong">
<label>The shop is now:</label>
<item><label>Open</label><value>open</value></item>
<item><label>Closed</label><value>closed</value></item>
</select1>
<submit submission="change"><label>OK</label></submit>
- The page must be correct XHTML (not HTML)
- The server must accept the "put" method
Demos
FoaF
interface (link is to an out-of-date version)
Webservices
interface
Implementations
- At release XForms had more implementations announced than any other W3C
spec had ever had at that stage
- Different types of implementation:
- plugin
- native
- 'zero install'
- proxy
- Many big players doing implementations, e.g.
"The age of the fat client is past" -- an implementor
More Information
The origin: www.w3.org/Markup/Forms, and if your company is a member:
www.w3.org/Markup/Forms/Group
XForms: http://www.w3.org/TR/xforms/
XPath: http://www.w3.org/TR/xpath
XPath quick reference:
http://www.mulberrytech.com/quickref/XSLTquickref.pdf
XML Events: http://www.w3.org/TR/xml-events/
validator: www.xformsinstitute.com