Sidebar: What's SOA? Think eBay

Computerworld - To help understand SOA, I like to use the example of eBay. Thousands of people shop on eBay Inc.'s online auction site every day, hoping to find exceptional deals on merchandise offered by eager sellers. EBay acts as the middleman, providing an integrated service to connect buyers and sellers through one common interface.

There are several reasons why eBay is so successful. First, it's easy to use. It doesn't take much time or effort to set up an account to buy and sell. Second, it's a one-stop shop for both buyers and sellers; a buyer, for example, is able to peruse a vast array of products in one place. Third, it's incredibly flexible. A buyer can act as a seller without establishing multiple accounts. Fourth, eBay provides all of the services, thereby insulating buyers and sellers from what is taking place behind the scenes.

If you understand these basic mechanics of eBay, then you're well on your way to understanding how a service-oriented architecture works.

Think of the applications in your company as buyers and sellers on eBay. Some applications are providers of information (sellers), while others act as consumers (buyers). These roles can and do switch, depending on the context of the transaction. One consuming application can just as easily be a provider to another consuming application.

To make it work, there must be a common, standards-based interface (similar to eBay's Web site) that both consumer and provider applications access to broker transactions. They communicate with one another via messages enabled by reusable services within the common interface rather than through point-to-point software that is tightly coupled.

Although this description is rudimentary, this is basically the way in which a service-oriented architecture functions.