Xforms Technology

What are XForms?

XForms are an MVC-based declarative client-based technology for capture, validation, calculation and assessment of user data. In application they're a cross between a spreadsheet and XSLT.

XForms are defined by an open W3C standard that will become standard in XHTML 2.0, but their implementation is already available for all browsers via a tiny (77KB) GPLed javascript or tinier (60KB) Flash module.

Purpose

Thin client XForms can

bind data to an xml file
auto-generate from XML schemas
validate against schema data types
respond to user input in real time (versus submission time)
enforce relations amongst entries
prefill, save and restore values to and from a file
modify the style of each control depending on the device they are displayed on (browser versus mobile versus voice, etc.)
require specific user interactions and inputs
disable input controls depending on circumstances and work states
change sections of a form depending on circumstances and work states
input variable length arrays of data
output entries and quantities derived from entries
submit the same form to different servers
integrate directly with Web services using SOAP
send validated result data directly to a server in XML format.

For all these application behaviours XForms require no client or server-side procedural code or scripts - they are pure declarative XML.

Architecture

XForms architecture is based on a spreadsheet-like declarative calculation model that keeps track of computational dependencies so chained calculations properly resolve themselves in unison with changing input data. Calculation resolutions can include CRUD operations on the underlying XML model as well as all the usual arithmetic and logical calculations on all the usual datatypes.

XForms use XML to define model data, XPath to bind to XHTML user interface views, and XML Events to adorn this binding with GUI and programmatic controllers. This creates the classic MVC application pattern - any GUI gesture can be mapped to recalculation, revalidation, refresh, scrolling, filtering, or other behaviours of repeating line item tables, and to declare and execute embedded Editors, Unit Tests, and User Acceptance Tests for these mappings - directly in the XML without any procedural scripting.

Pub-sub logic is also fully realizable with XML Events, removing the need for a client-side procedural application backbone. This is not to say XForms is intended to replace all scripting - there will likely still be scripts for GUI special effects and exotic validations. But economical replacement of about 80% of procedural scripting is plausible. And this is just scratching the surface.

Interoperation

As a standard XForms are platform and device independent. As part of XHTML 2.0 they automatically integrate with

WML - mobile phones & handhelds - free Oracle player
VoiceXML - spoken, automated call-center web data - free IBM player
SVG - Scalable Vector Graphics for display of histograms and other graphs - about a dozen players
XML Signatures - digital signatures for XML
Braille devices, and other new output modalities.

Likewise XForms input is not restricted to keyboard and mouse but can take input from

scanners and digital cameras
microphones
pens and digitizers
video sources
3D input devices
biometric input devices