XForms: A case studyRajiv 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 web-service– 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

WSDL

Servlet

Parses

XFORMBuilds Chiba

Renders

BrowserUser Enters Data

Invokes Operation Response

Described By

1

2

3

4

5

67

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