Catching up on XForms, XRX, XProc, and Orbeon

I recently spent a little time looking at open source components we could assemble to provide a basic web form authoring solution embedded within one of our SaaS offerings. Rather than full-blown Web Content Management, all that the solution really called for was the ability for non-technical users to enter data in a form and to upload binary objects which may be related in some way to that form data. There could be several forms with some chunks of forms being reused, and at some point, it might be nice for non-technical people to create their own forms.

For the forms piece I immediately thought of XForms because (1) I knew we wanted the data stored as XML and (2) I like the MVC pattern that XForms follows.

It had been a while since I played with XForms directly. Alfresco’s web forms engine is currently based on the Chiba implementation of XForms, but you don’t normally get exposed to the XForms details. There are a few things going on in the world of XForms that caught my attention:

XProc. XProc is a W3C specification for an XML Pipeline Language. If you’ve ever worked with Apache Cocoon you’ll get this concept immediately as Cocoon was an early implementor of the XML pipeline approach. Think of raw XML going in a pipeline on one end, having it processed with one or more steps as it goes through the pipeline, and then possibly new XML emerging from the other end. Those processing steps can be thought of as modules that can be reused and recombined in different ways to build new pipelines.

One of our past clients was doing something similar to this with their own home grown solution. They were taking XML data feeds from sporting events, and then performing various operations on that XML before it was eventually posted on the web site in the form of scoreboards and stats pages. They called the process definition a “workflow” and it was described in XML. XProc would be ideal for something like that.

XRX. XRX stands for XForms/REST/XQuery. It is not a standard–it’s an approach for building web applications. It means using XForms on the front-end to present and capture data, REST between the front-end and the back-end, and XQuery to retrieve and transform XML from the back-end. This approach allows you to build a web application without any object-relational mapping. The data you are dealing with is always XML so there is no translation necessary.

eXist. eXist is an open source, native XML database. If you’re dealing exclusively in XML, why go to the trouble of translating your XML into rows and columns (and then back in to XML when it is retrieved)? Native XML databases do a better job of storing XML with no translation required while preserving your ability to efficiently do things like XQuery and XPath statements across the entire scope of your dataset. I had previously played with Apache Xindice but Xindice doesn’t support XQuery which is a major focus for eXist (plus, things seem a little quiet over at the Xindice project).

Orbeon Forms is a server-side XForms implementation. If you’re looking for an open source forms solution, you need to take a look. Orbeon is XForms, XProc, and eXist, all rolled into a single offering. You can merge the Orbeon WAR file with your web app’s WAR or you can deploy Orbeon in its own web app and simply tell it to handle all of the XForms tasks. Orbeon also has a graphical forms builder but I didn’t get a chance to play with that.

Thinking I might want to use Apache Sling/Jackrabbit as my repository, I decided to see how easy it would be to persist the XForms data into Jackrabbit instead of eXist, as Orbeon’s tutorial does by default. As I suspected, it turned out to be a 2 minute task. Because Sling provides a REST API into Jackrabbit, and because XForms can persist data via REST natively, it was simply a matter of changing the post URL from the eXist REST URL to the Sling REST URL and it was a done deal. Deciding whether or not Jackrabbit (instead of or in combination with eXist) is the right way to go is a decision for another day.

I’ll provide an update at some point down the road after we’ve done some implementation work on this embedded forms stuff and we’ll see how it actually held up.

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