May 3, 2006, mid-afternoon. The second Internet Identity Workshop had just wrapped up. It was so thick with sessions and discussions that Paul Trevithick, Andy Dale, and I just kept passing each other in the halls saying, “We need to talk!” but never having the time to actually do it.

We finally agreed to meet in one of the conference rooms after the main event was over. We migrated to a whiteboard and started drawing pictures to help us answer the key questions that kept coming up over the past two days, “How exactly are Higgins and XDI different? What does Higgins do that XDI doesn’t and vice versa?”

There was great irony in this. Besides heading the Higgins project, Paul is a member of the XDI Technical Committee (TC) at OASIS. Besides being the leading implementer of XDI, Andy has been a member of the Higgins project. And I’ve been working with both of them for several years now. Yet still none of us had a really good answer to this question.

As we kept drawing and redrawing the diagrams on the whiteboard, wrestling with how things lined up, I noticed Kaliya, Doc Searls, Phil Windley (collectively the organizers of IIW), plus several other late-stayers had joined the room and were happily monitoring to our progress. They were as interested in the outcome as we were!

I stil remember the late afternoon sun streaming in though the second-story window of the Computer History Museum as I pondered that whiteboard. All three of us had the unsettling feeling that there was much more to this story than we were able to divine off this particular diagram at this particular time. And then poof, our fifteen minutes was up and we all had to split for our respective trains, planes, and automobiles.

But the question was NOT answered, and it kept gnawing at the three of us. It was still there at Digital ID World in September, only now it was starting to surface in another direction: the relationship of OpenID 2.0 (which supports XRI) and Higgins. Could Higgins support both OpenID authentication and CardSpace authentication of the same digital subject? If so, was a URL or an XRI the common identifier of the subject? And how would this relate to attribute sharing?

Again the three of us swore we needed to get in a room together to get to the bottom of this and finally answer these questions – for ourselves, and for everyone else that was asking. We even knew of at least one context where we might get that opportunity – a new project from Paul Hawken’s Natural Capital Institute called WISER (World Index for Social and Environmental Responsibility) that will provide an indexing and data sharing platform for the entire international NGO/civil society sector. It looked like an effort on which we could all collaborate.

Still it took until December for the WISER Commons project to gel to the point where we could finally schedule three days together last week to develop a recommended identity and data sharing architecture for WISER.

As planned, the first day we spent understanding the requirements of this groundbreaking project (about which I’ll blog more soon). This gave us just what we wanted: several flagship use cases against which we could compare the Higgins and XDI architectures in detail. The next morning we sequestered ourselves in front of a white board in a conference room at Andy’s offices. We took the first use case and started diagramming it. Step by step by step we worked through how it would be implemented using the Higgins framework and the XDI protocol. But this time, where before we had drawn big boxes and circles and arrows…we started drilling down. Blowing up each box into its subcomponents and drawing the next level of circles and arrows…and when we got stuck, drilling down to yet another level below that.

As expected, there was a boatload of terminology frustration on both sides. Higgins uses “context”, “contextref”, “digital subject”, “subjectref”, and “context-unique ID” or “CUID”. XDI uses “authority”, “type”, “instance”, “i-name”, “i-number”, and “cross-reference”. But as we slowly peeled the onions, we began recognizing intersection points from which we could start mapping the terms.

For example, we knew going into it that both Higgins and XDI were based on schema-independent, context-independent data models, and those models are fundamentally based on RDF subject/predicate/object graphs. But it wasn’t until we peeled the onion all the way down to these core data models and started drawing the RDF graphs that we found ourselves not only on solid ground…

…but common ground. Acres of it. Whole continents of it. In fact, as we used to say at the gold dredging operation where I worked in Alaska, we hit bedrock – and that bedrock extended all the way under the mountain range.

Suddenly for the first time we were no longer looking at each other as “the other way of doing it”. Instead we saw we were both on the same side, building fundamentally the same thing: an interoperable way of sharing data between any two systems and applications.

The next morning when we reconvened with the WISER Commons team we hit upon the perfect analogy: it was exactly like the transcontinental railway projects in the 1800s. Higgins was building from East to West (Paul being from Boston), i.e., from the user-interface and application layer down towards the protocol layer (Paul coming from a background in page layout and desktop publishing). Andy and I and the rest of the XDI TC had been building from West to East (Andy being based in Berkeley and me in Seattle), i.e., from the protocol layer up towards the application and UI layer (Andy coming from the enterprise database and messaging world).

And although we had been building two entirely different railroads for moving data from coast to coast, suddenly here we were, meeting in the middle of the continent. And, to our mutual astonishment, finding that we were both using the same guage tracks! In other words, with a little work, you could hook the two together and data would flow as smoothly up and down the Higgins/XDI stack and across Higgins/XDI-enabled systems as steam locomotives could move across the interconnected intercontinental railway system.

The secret was the guage itself – RDF. We had both arrived at it as the common core model for data description. And although the railroads we have respectively built from it have many different features and can go different speeds and handle different types of passengers and freight in different ways, they are fundamentally interoperable.

So we dubbed this “The Golden Spike Meeting” of Higgins and XDI (Laurie Rae informs me that in Canada it was called “The Last Spike”, but there’s something more romantic about a golden spike). And hopefully it will represent as important a milestone in our progress towards an open interoperable data sharing layer for the net. At a minimum you can know that Paul and Andy and I are committed to bolting these trains together as quickly and efficiently as possible and showing for real how the data can just start moving.

All aboard!!