When Matt and I first proposed the standardized interface for pencil discovery and ordering, we only intended to write a few articles on the concept and then let the whole idea more or less die. Then, the strangest thing happened—we realized we wanted to keep running with the idea. Actually, the realization came in a moment of serendipitous inspiration: To build the system mentioned in our last installment, the WSDL files that describe the pencil-related interfaces would have to contain some more features. In short, the interface would have to evolve—and we could talk about an issue that will soon be a high priority for many Web service developers: versioning. If you look at the documentation, articles, and books that have gone out about Web services, they spend little time talking about successive versions of a Web service.
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