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XForms: A case study
Rajiv Shivane & Pavitar Singh
Building a generic Web-Service client
• Problem statement:
Need to build HTML forms for invoking operations
on any web-service given it’s WSDL
– Web services defined using WSDL
– Operations are declared in WSDL
• Why XForms
– Single Servlet to generate HTML for invoking any webservice
– Generates dynamic forms for Collection data types
– Ease of invoking web-service as submitted data is in XML
format
– Built in validation framework
Implementation overview
WebService
1
Described
By
Invokes
6
Operation 7
Response
WSDL
Enters
5 User
Data
Parses
Browser
4
Renders
2
Servlet
Builds
3
XFORM
Chiba
Sample input-form for an operation
Form populated with web-service response
How Easy it is
XForms: An introduction
What is XForms ?
– Next generation web forms from W3C
– W3C Recommendation since October
2003
– Aims at replacing HTML forms
– But supports any host language
XForms Goals
• Make Web form design easier
– Less client-side (JavaScript) code
– Less server-side code
– More functionality!
• Capture data from end-user in XML
Problems with HTML Forms
• Dependence on Scripting Languages Like Java Script
and VB Script to do common tasks
–
–
–
–
–
Marking Required Controls
Validations
Calculations
Error Messages
Conditional Layout
• Difficulty of Initializing Form
• Can Represent Only Flat Data (Name Value Pairs)
• Reintrepreting Data Format at every stage of
workflow
Conceptual Structure of XForms
Sample XForm
Model Section
• Model Element in Xforms Document
• Contain Child Elements
– Instance
– Bind
– Submit
Bind
Model Section
•
•
•
•
•
•
Encapsulates Data Aspects of a Form
Uses XML Schema to Define Constraints
Uses Xpath to Define Model Properties
Captures What, How and Where to submit
Enable Reactive User Interfaces
Encourage declarative authoring
UI Controls
UI Controls
• Connects User Interface to the Model
• Uses Xpath to address nodes in the instance
• UI controls collects user input
• Bind to underlying model
• Controls are designed for accessibility
• Abstract Controls encourage Device
Independence
UI Controls
UI Controls
UI Controls
UI Controls
UI Controls
UI Controls
Complex User Interfaces
• Aggregation construct <group>
– Group logically related user
– Enables Refactoring
Complex User Interfaces
• Dynamic User Interaction with <switch>
– Enables any of logically groups to be selectively displayed
to the User
– Use declarative Event Handler <toggle>
Complex User Interfaces
• Repeating structures with repeat
– Very powerful construct
Event Handlers
Events
•
•
•
•
Bring User Interface to life
Give access to eventing via XML Events
Attach Dynamic Behavior
Obviate common use of scripts via declarative
actions
Events Categories
• Initialization
– Events raised as various Xform components are initialized
• Interaction
– Raised by user interaction
• e.g Request for a Help
• Notification
– Raised by Xforms processing model
– To trigger different steps in Xforms processing
• Errors
– Raised when specific type of error conditions are
encountered
Native Xform Support in Web Browsers
• Microsoft doesnt want to support it
– Competing with InfoPath
• Mozilla/Firefox Support
– In the works but not yet deployed
– But still market share under 10%
• But is That a Problem if we want to implement
XForm ??????
The Solution
• Server-side emulation layer A/K/A server-side
XForms
• Developer writes XHTML and XForms, as he would
with an XForms-aware web browser
• Server-side XForms engine translates this into
(X)HTML, CSS, and lightweight JavaScript
• Uses AJAX to achieve asynchronous validation
Implementations for Server Side XForm
• Orbeon PresentationServer (OPS)
• Chiba
→ Both are open source
Thanks
Q&A