What Are XForms
by Micah Dubinko | Pages: 1, 2
Actions sans Script
Other than a few special cases (submit and reset) the way to make
today's web forms do something is through scripts attached to
"intrinsic" event attributes like
onFocus. With the
mission of reducing the need for scripts, the HTML Working Group and
XForms Working Group have jointly developed a general purpose event
framework called XML
Events. It provides an XML interface to DOM Level 2 STYLE
events. It also enables the definition of markup-based
(a.k.a. script-free) XForms Actions.
Using an element-based declarative syntax, XForms authors can:
- set focus to a form control
- display a message to the user
- navigate to a new URI (in the same or a new window)
- change the value of an instance data node
- force a recalculation, revalidation, or screen refresh
- submit or reset all or a portion of the instance data
- perform other actions to deal with scrolling and manipulating repeating line item tables
In this example, a form authored for a resource-limited device might wish to recalculate only when a trigger is activated:
<xforms:trigger> <xforms:label>Click to Recalculate</xforms:label> <xforms:action ev:event="xforms-activate"> <xforms:recalculate/> </xforms:action> </xforms:trigger>
(Note that the
xforms prefix represents the XForms namespace and
ev prefix represents the XML Events namespace.)
While the XForms language is suitable for inclusion in any number of other XML document formats, the sweet spot is its combination with XHTML. Working Drafts of XHTML 2.0 indicate that the old forms technology will not be included in the standard, being replaced by XForms.
The following example will walk through a basic form -- collecting a credit card number in the simplest way possible.
In XHTML, a form is completely enclosed within
<form>...</form> tags. In contrast, the
XForms solution separates purpose, represented by the "XForms Model"
(the name for the non-visible form data plus annotations),
from presentation, represented by the form controls. This means that
adding a single form to a containing document usually involves
inserting markup in multiple places.
The XForms Model belongs in the header section or
element of XHTML:
<html xmlns="http://www.w3.org/2002/06/xhtml2" xmlns:xforms="http://www.w3.org/2002/08/xforms/cr"> <head> <title>Example of XHTML plus XForms</title> <xforms:model id="myform"> <xforms:submission action="https://example.com/cc-submit"/> </xforms:model> </head>
Additionally, form controls belong alongside other markup in the visible portion
of the document, which means the
<body> element in XHTML:
... <p>Enter your credit card number below</p> <xforms:input ref="cc"> <xforms:label>Credit Card:</xforms:label> </xforms:input> <p>...</p> <xforms:submit> <xforms:label>Submit</xforms:label> </xforms:submit> ...
Initially, HTML forms didn't associate any kind of field-level
label with form controls, except for physically positioning the
labels near the controls, which was especially difficult for
non-visual browsers to interpret. Later versions added an optional
label wrapper, but this technique never gained widespread usage. Now
in XForms, every form control element has a required
label child element, which contains the associated
Upon submit, the XForms Processor would deliver serialized instance data -- which looks something like
<instanceData> <cc>123423453456</cc> </instanceData>-- where the element name is determined by the binding expression attached to the
inputelement. In more advanced settings, separate instance data can define arbitrarily complex XML structures processed through XForms.
What does the future hold for XForms? One certainty is that connected devices are becoming more diverse than ever, appearing in all shapes and sizes. Web forms no longer lead sheltered lives on the desktop. By offering a more flexible, device-independent platform, XForms will provide interactivity on such devices.
Most organizations now have substantial investments in XML. Since XForms technology reads and writes XML instance data, it enables existing investments to be leveraged as building blocks in a larger system more smoothly than with ordinary XHTML forms. Additionally, Web Services (or the Semantic Web, depending on your upbringing) will increase the amount of information interchange over the Web, which will in turn increase the need for information to be entered -- through XForms.
Those who have struggled with traditional forms and associated scripting will appreciate the consistent set of form controls and declarative actions in the specification, as well as the powerful and familiar XSLT-like processing model. Calculations, validations, and business logic will also be expressible without scripts.
Updated forms are one of the major changes in XHTML 2.0, the most significant change to HTML since its conception in 1993. Developers and users alike are looking forward to the final W3C Recommendation for XForms.
The primary source for information on XForms is the www-forms mailing list. To subscribe, send an email to firstname.lastname@example.org with the word "subscribe" in the subject line (include the word "unsubscribe" if you want to unsubscribe). The archive for the list is also accessible online.
To play with the latest XForms specification, you can use the latest published Schema, or try out one of the following early implementations:
The open source X-Smiles browser supports an impressive array of standards, including XForms, SVG, SMIL, and XSL formatting objects. E-XMLMedia has developed a Java applet-based version, which is available as a commercial product, with an evaluation version available upon request. Additionally, Mozquito is working on a Flash implementation, with details posted on an editable weblog done in XForms. (Warning: this link requires an XForms browser) More implementations are coming online soon.
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