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 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 XFORM Builds Chiba Renders Browser User Enters Data InvokesOperation Response Described By

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

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

Complex User Interfaces Aggregation construct –Group logically related user –Enables Refactoring

Complex User Interfaces Dynamic User Interaction with –Enables any of logically groups to be selectively displayed to the User –Use declarative Event Handler

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