That ⊂ symbol in the title of this post means "is a subset of": I thought about using the better-known ≠ ("not equal"), but that's too general. I didn't want to say that the Web and the Cloud are completely different, but rather that the Web provides only a partial view of what the Cloud contains.

What brings this to mind is the foofaraw over a recent, temporary loss of Web access to Gmail. As one might resignedly expect, this incident is being gloom-and-doomed with pronouncements like "cloud computing is a more tenuous proposition than I realized" -- although it's a relief to see that the vast majority of comments are more along the lines of Jessi Hempel's observation this morning that "Most e-mail goes down. According to Osterman Research, based in Black Diamond, Wash., e-mail systems in mid-size and large organizations have a mean of 53 minutes of unplanned down time in a typical month." Cloud services are, in general, vastly more reliable than on-premise alternatives.

But even Hempel's comment misses a key point. Gmail did not go down. If you were using an IMAP client such as an iPhone, or if you prefer the simplicity and diversity of using a POP interface, Gmail remained accessible by either of those means. People who assessed the risks of even an occasional interruption of access to cloud-based mail, and found those risks unacceptable, have always had -- and will continue to have -- many options for providing as much redundancy as they need for as much as they're willing to spend.

The point, therefore, is that the cloud is not the client: the cloud is the capability, regardless of how that capability is delivered to a person or incorporated into a process.

We take this point quite seriously here, because it's been at least two years since we passed the point where more than half of our workload is driven by requests to our APIs -- in addition to the work we do in response to the clicks and keystrokes of subscribers to our Web-delivered applications.

We continue to extend and refine those Web-interface capabilities, of course. After all, to turn the previous sentence around, Web interaction represents nearly half of what we do, so of course it's still important. But the salesforce.com cloud is twice the size of what our own applications' users directly see.

Over time, every mode of access to the cloud will become more ubiquitous, more powerful, more reliable, and more cost-effective. Three years ago, hand-held Internet access was like looking through a keyhole; three months later, the iPhone opened a window to the Web from almost anywhere.

The exponential curves (yes, "exponential growth" really does have a meaning) of connectivity have yet to show signs of a sigmoid slowdown -- unlike so many of the elements of the aging thick-client platform, which are clearly at the stage of diminishing returns.

If you're using the cloud as a consumer, you'll relish the low cost and continually improving convenience of Web interfaces. If you're using the cloud in the enterprise, you'll invest in additional services and technologies that reduce the number of single points of failure, and assure graceful degradation when things aren't working as well as they usually do.

Can you make on-premise solutions arbitrarily reliable? Well, you can always spend more money. Must you give up that freedom of choice in the cloud? Emphatically not -- but in the long run, any given level of information security and operational assurance will inevitably wind up costing less in the cloud.