Here's to the multi-tenant application, an invention of the Internet age and without which many of the low-cost services, such as search and travel reservations, would be impossible. And here's to the multi-tenant doubters, such as Oracle's Larry Ellison, who recently questioned its "weak security model" and its "co-mingling of competitors' data."

I'm going to claim an already strong innovation is going to get stronger. Maybe you don't really want to play such multi-user games such as Mafia Wars or Farmville or post to your co-workers' Facebook walls. Even so, you need multi-tenant applications. Without them, we'll need to throw a lot more money and computing resources at the services flowing out of the Internet that we've begun to take for granted.

The development of multi-tenant applications is still an emerging art. It requires a new and sometimes hard to achieve architecture. It can't simply mimic the multi-layered, monolithic enterprise application.

Most of all it has to scale easily to thousands or hundreds of thousands of users. It simply won't do to start up 10,000 instances of an application to satisfy 200,000 concurrent users. The multi-tenant application is the champion of concurrency, and in the Internet age, that makes it better, cheaper, and faster.

Google is a multi-tenant application, if there ever was one. Its design in some respects remains unique, although most multi-tenant applications learn lessons from Google's and eBay's examples.

The more prosaic customer relationship management (CRM) apps offered by Salesforce.com, Netsuite, and SugarCRM are also multi-tenant; multi-tenancy lies at the heart of software-as-a-service, and it's the potential competition coming from that quarter that seem to inspire Ellison's ire.

Oracle has held the number two position in the CRM market, behind SAP, according to Gartner statistics for the year 2008. Salesforce.com was third with 10.6%. Microsoft was fourth with 6.4%. Oracle's application customer base was growing by acquisition. With both Salesforce and Microsoft offering SaaS versions, CRM-as-a-service had grown from 15% of the market in 2007 to 20% in 2008. In all likelihood, that pace of growth continued in 2009 and continues in 2010.

Both Salesforce.com and Microsoft are growing through the acquisition of new application customers, while Oracle grows primarily by acquiring other application companies, concluded InformationWeek Analytics as a result of a survey of 485 application users in January. With Ellison so heavily invested in traditional applications, it's possible to see why multi-tenant applications have found their way into his crosshairs.