You may have heard the phrase "software as a service" and wondered about its meaning. The term service, in day-to-day usage, refers to what you get from a service provider. For example, you bring your dirty clothing to a cleaner to use its cleaning service. Software, on the other hand, is commonly thought of as an application, either an off-the-shelf product, or a custom application developed by a software firm. You typically buy the software (or in our case, build the software). It usually resides on some sort of media such as floppy diskette or CD and is sold in a shrink-wrapped package through retail outlets, or, in the case of a web application, the software application is not distributed, but is accessed through a browser.
How can software be viewed as a service? The example we are about to describe might seem far-fetched; however, it is possible with current technology. Imagine the following. As you grow more comfortable with the Internet, you might choose to replace your computer at home with something like an Internet Device, a large-screen PDA designed for use with the Internet. Let's call the device an iDev. Let's suppose that with this device, you can be on the Internet immediately through your cell phone, WiFi, or some other means. When you want to do word processing, your iDev is configured to print to a Microsoft Word service somewhere in Redmond, so you can type away without the need to install word-processing software. When you are done, the document can be saved at an iStore server where you can later retrieve it. Notice that for you to do this, the iStore server must host a software service that allows you to store documents. Microsoft might charge you a service fee based on the amount of time your word processor is running and the features you use (such as the grammar and spell checkers). The iStore service charges might vary based on the size of your document and how long it is stored. Of course, none of these charges would come in the mail, but rather through an escrow service where the money would be withdrawn from your bank account or credit card.
As long as your document is in a standard format, such as XML, you're free to switch word processors at any time. Of course, the document that you store at the iStore server is already in a standard data format. Since iStore utilizes the iMaxSecure software service from a company called iNNSA (Internet Not National Security Agency), the security of your files is assured. And because you use the document storage service at iStore, you also benefit from having your document authenticated and decrypted upon viewing, as well as encrypted at storing time.
While this particular vision of software as a service has yet to be realized, a variety of for-fee and free services have begun to appear. In early 2001, Microsoft announced plans for an integrated collection of consumer-oriented services (known first by their codename, "Hailstorm," and later as ".NET My Services") but was forced to abandon the initiative for a variety of reasons, some technical and others legal, political, or market-related. Today, Microsoft offers a variety of user-centric services for identification and authentication, email, instant messaging, automated alerts, calendar, address book, and personal information storage. These are available through its MSN online services, and through Passport (http://www.passport.net), Alerts (http://alerts.microsoft.com), MSN Wallet (http://wallet.msn.com), and Hotmail.
Of greater interest to developers, however, is the availability of these services for use as building blocks in third-party web applications. Hosted by Microsoft and known as Microsoft .NET Services, Passport, Alerts, and MSN Wallet can each be licensed and incorporated into any application that adheres to XML web services standards, regardless of platform. A more recently announced web service is Microsoft MapPoint .NET, which is a set of services that allows you to incorporate maps, driving directions, distance calculations, proximity searches, and other location intelligence into your applications.
In addition to Microsoft, other companies are beginning to offer information and functionality as services over the Web. A recent poster child is Saleforce.com, which offers customer relations management (CRM) software over the Web, either as a standalone product or as a set of services that can be incorporated into third-party applications. The Liberty Alliance is at work defining an authentication service that can be offered as an alternative to Microsoft Passport. And both Google and Amazon now make portions of their business information available through public web service interfaces.
The potential for consumer-oriented and business-to-business web services like Microsoft .NET Services is great, although there are serious and well-founded concerns about security and privacy. In the mean time, web services can be great in interoperability areas where there are needs to expose legacy functionalities or to enable interaction between multiple heterogeneous systems. In one form or another, though, web services are here to stay, so let's dive in and see what's underneath.