In this sense, applications provide services to each other. The role of the Web is central to this vision. A typical EDI connection, for example, would be planned months in advance, and would provide a robust durable connection between just a pair of applications, typically in two separate organizations. Web Services suggests a much more dynamic and fluid model of interconnection, one that provides for applications the same flexibility that the Web has already brought to human users. Purchasing applications can be coded to connect dynamically to new suppliers, possibly selected from a continually changing directory of approved sources.
Fulfillment applications can establish dynamic connections to shippers, and so on.
This dynamic model of interconnection on a global scale presents new and unique challenges. Web Services thus depend on the ability to provide appropriate security, reliability, and manageability to an extraordinarily broad range of organizations, dispersed throughout the world. The nature of the applications suggests that transactions, when used, will often be long running. Security mechanisms must interconnect rather than encapsulate systems which themselves use a broad range of security technologies. All of this must be done for applications which connect to each other dynamically and involving a continually changing set of organizational relationships on a global scale.